Common questions about Vaillant codes · Search all brands by code or symptom
What is safe for you to do
Every code here follows the same safety rules. You can:
- press the reset button once, as your user guide shows;
- for low-pressure codes, top up the pressure with the filling loop, as your user guide shows;
- for ignition and flame-loss codes, check the gas is on at the meter and a prepayment meter has credit;
- thaw a frozen plastic condensate pipe outside with warm (not boiling) water;
- check the thermostat, timer and power to the boiler.
Never open the boiler casing. Only a Gas Safe registered engineer may work inside a gas boiler. Codes marked Engineer after one reset have no homeowner fix: reset once, then leave them to an engineer. Codes marked Safe checks first list the one check that relates to that code.
ecoTEC plus (VU / VUW ..6/5-5, combi and system)
Vaillant boilers show F. followed by a number, e.g. F.28. S. codes are status codes, not faults.
Source: ecoTEC plus Installation and Maintenance Instructions (VU, VUW ..6/5-5), doc. 0020244997_07 (15.07.2021), pp. 60–62, Appendix E Overview of fault codes. Open the manual (PDF) (Manufacturer copy)
Ignition / flame
F.26 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Fault: the gas valve stepper motor is not working or not connected.
Likely causes
Gas valve stepper motor, plug or wiring.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.26 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.26 means the gas valve stepper motor is not working or not connected. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.27 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Safety shut-down: flame simulation. The flame sensor reports a flame that should not be there.
Likely causes
Gas pressure, the monitoring electrode, the board or a gas solenoid valve.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.27 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.27 is a safety shut-down: flame simulation. Likely causes include gas pressure, the monitoring electrode, the board or a gas solenoid valve. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.28 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Start-up failure: ignition unsuccessful.
Likely causes
Gas off or low gas pressure, an empty prepay meter, a frozen or blocked condensate pipe, a blocked air intake or flue, or an ignition lead, electrode or board fault.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.28 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.28 is listed in the manufacturer's table as "Start-up failure: ignition unsuccessful". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.29 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Operating failure: the flame went out and re-ignition failed.
Likely causes
An intermittent gas supply, flue gas recirculation, a blocked condensate pipe, earthing or the gas valve cable.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.29 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.29 is listed in the manufacturer's table as "Operating failure: the flame went out and re-ignition failed". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.54 Vaillant ecoTEC plus
Safe checks firstIgnition / flameWhat it means
Fault at boiler start: no or insufficient gas inlet pressure.
Likely causes
Gas supply pressure (often with F.28/F.29), the gas valve, plug or harness.
What you can safely do
Check another gas appliance such as the hob works, the gas meter valve is on and, on a prepayment meter, there is credit. In freezing weather, check the plastic condensate pipe outside: if it is frozen, pour warm (not boiling) water along it. Then press reset once. If the code comes back, stop resetting.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the gas supply is fine and the code returns after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.54 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.54 is listed in the manufacturer's table as "Fault at boiler start: no or insufficient gas inlet pressure". Check another gas appliance works, the meter valve is on and any prepay meter has credit, then reset once. If it returns, book a Gas Safe registered engineer.
F.61 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Fault: the gas valve cannot be actuated.
Likely causes
Gas valve harness, plug or valve.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.61 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.61 means the gas valve cannot be actuated. Likely causes include gas valve harness, plug or valve. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.62 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Fault: the gas valve is slow to shut off after the flame goes out.
Likely causes
Gas valve, burner surface, harness or board.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.62 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.62 means the gas valve is slow to shut off after the flame goes out. Likely causes include gas valve, burner surface, harness or board. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.67 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Implausible flame signal.
Likely causes
Harness, flame monitor or board.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.67 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.67 is listed in the manufacturer's table as "Implausible flame signal". Likely causes include harness, flame monitor or board. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.68 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Unstable flame signal.
Likely causes
Air ratio, gas pressure, a condensate blockage, the gas injector, the ionisation circuit or flue gas recirculation.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.68 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.68 is listed in the manufacturer's table as "Unstable flame signal". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.92 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Incorrect gas type: the coding resistor does not match the gas group entered.
Likely causes
Coding resistor or gas group setting.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.92 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.92 is listed in the manufacturer's table as "Incorrect gas type: the coding resistor does not match the gas group entered". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.93 Vaillant ecoTEC plus
Engineer after one resetIgnition / flameWhat it means
Combustion quality outside the permitted range.
Likely causes
Gas injector, flue gas recirculation, gas group or a blocked pressure point.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Ignition and flame faults involve gas, so this is engineer-only.
What does F.93 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.93 is listed in the manufacturer's table as "Combustion quality outside the permitted range". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
Water pressure / circulation
F.22 Vaillant ecoTEC plus
Safe checks firstWater pressure / circulationWhat it means
Safety shut-down: low water pressure.
Likely causes
Not enough water in the boiler or system, the pressure sensor, or the pump or sensor cable.
What you can safely do
Look at the pressure gauge while the boiler is cold. If it is below about 1 bar, top it up with the filling loop exactly as your user guide shows, to about 1–1.5 bar or the figure in your guide, then close the loop fully. Check the radiator valves are open, then press reset once.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if you have to top up more than once every few months, the gauge goes above about 2.5 bar when hot, water drips from the outside overflow pipe, or the code returns after topping up.
What does F.22 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.22 is a safety shut-down: low water pressure. With the boiler cold, check the pressure gauge; if it is below the level in your user guide, top it up as the guide shows, then reset once. If it returns, book a Gas Safe registered engineer.
F.23 Vaillant ecoTEC plus
Engineer after one resetWater pressure / circulationWhat it means
Safety shut-down: the flow/return temperature difference is too large (water circulation too low).
Likely causes
Air or low water, sensors swapped, a blocked strainer, the pressure sensor or the pump.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if you have to top up more than once every few months, the gauge goes above about 2.5 bar when hot, water drips from the outside overflow pipe, or the code returns after topping up.
What does F.23 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.23 is a safety shut-down: the flow/return temperature difference is too large (water circulation too low). Reset once; if the code comes back, book a Gas Safe registered engineer and quote the full code. Do not open the casing.
F.73 Vaillant ecoTEC plus
Safe checks firstWater pressure / circulationWhat it means
The water pressure sensor reports the pressure as too low (signal too weak).
Likely causes
Low water pressure, the pressure sensor or wiring.
What you can safely do
Look at the pressure gauge while the boiler is cold. If it is below about 1 bar, top it up with the filling loop exactly as your user guide shows, to about 1–1.5 bar or the figure in your guide, then close the loop fully. Check the radiator valves are open, then press reset once.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if you have to top up more than once every few months, the gauge goes above about 2.5 bar when hot, water drips from the outside overflow pipe, or the code returns after topping up.
What does F.73 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.73 means the water pressure sensor reports the pressure as too low (signal too weak). With the boiler cold, check the pressure gauge; if it is below the level in your user guide, top it up as the guide shows, then reset once. If it returns, book a Gas Safe registered engineer.
F.74 Vaillant ecoTEC plus
Engineer after one resetWater pressure / circulationWhat it means
The water pressure is too high (sensor signal too strong).
Likely causes
Overfilled system or a faulty pressure sensor.
What you can safely do
Read the gauge. If it is above about 2.5 bar, check the filling loop is fully closed. Do not try to release water from the boiler yourself.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the pressure stays high or the code returns: an overfilled system, a letting-by filling loop or a faulty sensor need checking.
What does F.74 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.74 means the water pressure is too high (sensor signal too strong). Likely causes include overfilled system or a faulty pressure sensor. Reset once; if the code comes back, book a Gas Safe registered engineer and quote the full code. Do not open the casing.
F.75 Vaillant ecoTEC plus
Safe checks firstWater pressure / circulationWhat it means
Pump or water shortage: no pressure rise detected when the pump starts.
Likely causes
Air or low water, the pressure sensor or pump, or how the system and expansion vessel are connected.
What you can safely do
Look at the pressure gauge while the boiler is cold. If it is below about 1 bar, top it up with the filling loop exactly as your user guide shows, to about 1–1.5 bar or the figure in your guide, then close the loop fully. Check the radiator valves are open, then press reset once.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if you have to top up more than once every few months, the gauge goes above about 2.5 bar when hot, water drips from the outside overflow pipe, or the code returns after topping up.
What does F.75 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.75 is listed in the manufacturer's table as "Pump or water shortage: no pressure rise detected when the pump starts". Check the pressure gauge when cold and top up if low, as your user guide shows, then reset once. If it returns, book a Gas Safe registered engineer.
F.83 Vaillant ecoTEC plus
Engineer after one resetWater pressure / circulationWhat it means
NTC temperature gradient fault: the flow and return barely changed when the burner fired.
Likely causes
Not enough water in the boiler, or sensors with poor contact.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if you have to top up more than once every few months, the gauge goes above about 2.5 bar when hot, water drips from the outside overflow pipe, or the code returns after topping up.
What does F.83 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.83 is listed in the manufacturer's table as "NTC temperature gradient fault: the flow and return barely changed when the burner fired". Reset once; if the code comes back, book a Gas Safe registered engineer and quote the full code. Do not open the casing.
Temperature / overheat
F.20 Vaillant ecoTEC plus
Engineer after one resetTemperature / overheatWhat it means
Safety shut-down: the temperature limiter acted because the flow or return temperature got too high.
Likely causes
Flow sensor contact, poor pump circulation, or wiring.
What you can safely do
Let the boiler cool for 20 to 30 minutes, then press reset once. If the code comes back, leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Overheat shut-downs are safety devices doing their job, so this is engineer-only.
What does F.20 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.20 is a safety shut-down: the temperature limiter acted because the flow or return temperature got too high. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.24 Vaillant ecoTEC plus
Engineer after one resetTemperature / overheatWhat it means
Safety shut-down: the temperature is rising too fast.
Likely causes
Air in the heating circuit, low system pressure, the pump, the air vent or a stuck non-return valve.
What you can safely do
Let the boiler cool for 20 to 30 minutes, then press reset once. If the code comes back, leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code comes back after one reset. Overheat shut-downs are safety devices doing their job, so this is engineer-only.
What does F.24 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.24 is a safety shut-down: the temperature is rising too fast. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
Flue / fan / air
F.25 Vaillant ecoTEC plus
Engineer after one resetFlue / fan / airWhat it means
Safety shut-down: flue gas temperature too high.
Likely causes
Blocked flue, adverse wind, flue too long, low water, the pump or the safety cut-out wiring.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the terminal looks clear and the code returns. Flue and fan faults can affect how combustion gases leave your home, so this is engineer-only.
What does F.25 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.25 is a safety shut-down: flue gas temperature too high. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.32 Vaillant ecoTEC plus
Engineer after one resetFlue / fan / airWhat it means
Fan fault: the fan is faulty or not connected.
Likely causes
Fan plug, harness, fan blockage or speed, the Hall sensor, the board, or a blocked flue.
What you can safely do
There is no homeowner check that fixes this code. Write down the full code, press reset once, and if it comes back leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the terminal looks clear and the code returns. Flue and fan faults can affect how combustion gases leave your home, so this is engineer-only.
What does F.32 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.32 is listed in the manufacturer's table as "Fan fault: the fan is faulty or not connected". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
Sensors / thermistors
F.00 Vaillant ecoTEC plus
Engineer after one resetSensors / thermistorsWhat it means
Flow temperature sensor interruption: the sensor is faulty or not connected.
Likely causes
Sensor, plug, harness or board.
What you can safely do
Write down the full code. Check the boiler has power, then switch it off and on at its mains switch or press reset once. If the code comes back, leave it there: sensors are inside the casing.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Testing and replacing sensors means opening the casing, so this is engineer-only.
What does F.00 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.00 is listed in the manufacturer's table as "Flow temperature sensor interruption: the sensor is faulty or not connected". Likely causes include sensor, plug, harness or board. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.01 Vaillant ecoTEC plus
Engineer after one resetSensors / thermistorsWhat it means
Return temperature sensor interruption: the sensor is faulty or not connected.
Likely causes
Sensor, plug, harness or board.
What you can safely do
Write down the full code. Check the boiler has power, then switch it off and on at its mains switch or press reset once. If the code comes back, leave it there: sensors are inside the casing.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Testing and replacing sensors means opening the casing, so this is engineer-only.
What does F.01 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.01 is listed in the manufacturer's table as "Return temperature sensor interruption: the sensor is faulty or not connected". Likely causes include sensor, plug, harness or board. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.10 Vaillant ecoTEC plus
Engineer after one resetSensors / thermistorsWhat it means
Flow temperature sensor short circuit.
Likely causes
Sensor, plug, harness or housing short.
What you can safely do
Write down the full code. Check the boiler has power, then switch it off and on at its mains switch or press reset once. If the code comes back, leave it there: sensors are inside the casing.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Testing and replacing sensors means opening the casing, so this is engineer-only.
What does F.10 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.10 is listed in the manufacturer's table as "Flow temperature sensor short circuit". Likely causes include sensor, plug, harness or housing short. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.11 Vaillant ecoTEC plus
Engineer after one resetSensors / thermistorsWhat it means
Return temperature sensor short circuit.
Likely causes
Sensor, plug, harness or housing short.
What you can safely do
Write down the full code. Check the boiler has power, then switch it off and on at its mains switch or press reset once. If the code comes back, leave it there: sensors are inside the casing.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Testing and replacing sensors means opening the casing, so this is engineer-only.
What does F.11 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.11 is listed in the manufacturer's table as "Return temperature sensor short circuit". Likely causes include sensor, plug, harness or housing short. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.13 Vaillant ecoTEC plus
Engineer after one resetSensors / thermistorsWhat it means
Cylinder or warm-start sensor short circuit.
Likely causes
Sensor, plug, earth connection, harness or board.
What you can safely do
Write down the full code. Check the boiler has power, then switch it off and on at its mains switch or press reset once. If the code comes back, leave it there: sensors are inside the casing.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Testing and replacing sensors means opening the casing, so this is engineer-only.
What does F.13 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.13 is listed in the manufacturer's table as "Cylinder or warm-start sensor short circuit". Likely causes include sensor, plug, earth connection, harness or board. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.71 Vaillant ecoTEC plus
Engineer after one resetSensors / thermistorsWhat it means
The flow temperature sensor is returning implausible values.
Likely causes
Sensor contact or a faulty sensor.
What you can safely do
Write down the full code. Check the boiler has power, then switch it off and on at its mains switch or press reset once. If the code comes back, leave it there: sensors are inside the casing.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Testing and replacing sensors means opening the casing, so this is engineer-only.
What does F.71 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.71 means the flow temperature sensor is returning implausible values. Likely causes include sensor contact or a faulty sensor. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.72 Vaillant ecoTEC plus
Engineer after one resetSensors / thermistorsWhat it means
The temperature difference between the flow and return sensors is too great.
Likely causes
Sensor fault or poor thermal contact.
What you can safely do
Write down the full code. Check the boiler has power, then switch it off and on at its mains switch or press reset once. If the code comes back, leave it there: sensors are inside the casing.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Testing and replacing sensors means opening the casing, so this is engineer-only.
What does F.72 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.72 means the temperature difference between the flow and return sensors is too great. Likely causes include sensor fault or poor thermal contact. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.85 Vaillant ecoTEC plus
Engineer after one resetSensors / thermistorsWhat it means
Flow and return sensors fitted incorrectly.
Likely causes
Sensors swapped or fitted on the same pipe.
What you can safely do
Write down the full code. Check the boiler has power, then switch it off and on at its mains switch or press reset once. If the code comes back, leave it there: sensors are inside the casing.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Testing and replacing sensors means opening the casing, so this is engineer-only.
What does F.85 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.85 is listed in the manufacturer's table as "Flow and return sensors fitted incorrectly". Likely causes include sensors swapped or fitted on the same pipe. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
PCB / electrical
F.49 Vaillant ecoTEC plus
Engineer after one resetPCB / electricalWhat it means
eBUS fault: under-voltage on the control bus.
Likely causes
An overloaded or short-circuited eBUS, or two power supplies with different polarities.
What you can safely do
Write down the full code. Check the boiler has power and nothing else in the house has tripped, then switch the boiler off and on at its mains switch or press reset once. If the code comes back, leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Board, wiring and gas valve checks mean opening the casing, so this is engineer-only.
What does F.49 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.49 is listed in the manufacturer's table as "eBUS fault: under-voltage on the control bus". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.63 Vaillant ecoTEC plus
Engineer after one resetPCB / electricalWhat it means
EEPROM fault.
Likely causes
Board fault; the manual's fix is a new PCB.
What you can safely do
Write down the full code. Check the boiler has power and nothing else in the house has tripped, then switch the boiler off and on at its mains switch or press reset once. If the code comes back, leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Board, wiring and gas valve checks mean opening the casing, so this is engineer-only.
What does F.63 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.63 is listed in the manufacturer's table as "EEPROM fault". Likely causes include board fault; the manual's fix is a new PCB. There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.64 Vaillant ecoTEC plus
Engineer after one resetPCB / electricalWhat it means
Electronics or safety-relevant sensor fault.
Likely causes
Flow sensor or its cable, an unstable flame sensor, or the electronics.
What you can safely do
Write down the full code. Check the boiler has power and nothing else in the house has tripped, then switch the boiler off and on at its mains switch or press reset once. If the code comes back, leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Board, wiring and gas valve checks mean opening the casing, so this is engineer-only.
What does F.64 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.64 is listed in the manufacturer's table as "Electronics or safety-relevant sensor fault". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.65 Vaillant ecoTEC plus
Engineer after one resetPCB / electricalWhat it means
Electronics temperature fault: the electronics are faulty or too hot.
Likely causes
The board, or a hot environment around the boiler.
What you can safely do
Write down the full code. Check the boiler has power and nothing else in the house has tripped, then switch the boiler off and on at its mains switch or press reset once. If the code comes back, leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Board, wiring and gas valve checks mean opening the casing, so this is engineer-only.
What does F.65 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.65 is listed in the manufacturer's table as "Electronics temperature fault: the electronics are faulty or too hot". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
F.70 Vaillant ecoTEC plus
Engineer after one resetPCB / electricalWhat it means
Invalid device specific number (DSN).
Likely causes
Display and board replaced together without setting the DSN, or a coding resistor problem.
What you can safely do
Write down the full code. Check the boiler has power and nothing else in the house has tripped, then switch the boiler off and on at its mains switch or press reset once. If the code comes back, leave the boiler off.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if the code returns. Board, wiring and gas valve checks mean opening the casing, so this is engineer-only.
What does F.70 mean on a Vaillant ecoTEC plus boiler?
On a Vaillant ecoTEC plus, F.70 is listed in the manufacturer's table as "Invalid device specific number (DSN)". There is no homeowner fix for this. You can reset once, but do not open the casing; book a Gas Safe registered engineer and quote the full code.
Common questions
About Vaillant fault codes
2 questions
Which Vaillant fault codes can I usually deal with myself?
On the Vaillant ranges in our guide, only these codes have a safe homeowner check first: F.54 for gas supply or flame loss (check the meter and credit); F.22, F.73, F.75 for low pressure (top up). Reset once afterwards. Every other code needs a Gas Safe registered engineer; never open the casing.
Where can I find the official fault code list for my Vaillant ecoTEC plus?
Vaillant publishes the fault table in the installation and servicing manual for the ecoTEC plus (0020244997_07 (15.07.2021), pp. 60–62). CombiCert's fault code guide explains 34 codes from it. Check your data badge matches this model first, because codes differ between ranges. Write down the exact code before resetting, so the engineer can diagnose it faster.
Codes by type: ecoTEC plus (VU / VUW ..6/5-5, combi and system)
6 questions
Which Vaillant ecoTEC plus fault codes relate to the flue, fan or air supply?
On the Vaillant ecoTEC plus, the manufacturer's table has 2 flue, fan or air supply codes: F.25, F.32. None of these has a homeowner fix beyond one reset. Do not open the casing; book a Gas Safe registered engineer and quote the full code.
Which Vaillant ecoTEC plus fault codes mean the boiler will not light or loses its flame?
On the Vaillant ecoTEC plus, the manufacturer's table has 11 ignition or flame codes: F.26, F.27, F.28, F.29, F.54, F.61, F.62, F.67, F.68, F.92, F.93. For F.54, first check the gas meter, prepay credit and another gas appliance, then reset once. The others need a Gas Safe registered engineer.
Which Vaillant ecoTEC plus fault codes point to a control board or electrical fault?
On the Vaillant ecoTEC plus, the manufacturer's table has 5 control board or electrical codes: F.49, F.63, F.64, F.65, F.70. None of these has a homeowner fix beyond one reset. Do not open the casing; book a Gas Safe registered engineer and quote the full code.
Which Vaillant ecoTEC plus fault codes point to a temperature sensor fault?
On the Vaillant ecoTEC plus, the manufacturer's table has 8 temperature sensor codes: F.00, F.01, F.10, F.11, F.13, F.71, F.72, F.85. None of these has a homeowner fix beyond one reset. Do not open the casing; book a Gas Safe registered engineer and quote the full code.
Which Vaillant ecoTEC plus fault codes mean the boiler is overheating?
On the Vaillant ecoTEC plus, the manufacturer's table has 2 overheat codes: F.20, F.24. None of these has a homeowner fix beyond one reset. Do not open the casing; book a Gas Safe registered engineer and quote the full code.
Which Vaillant ecoTEC plus fault codes relate to water pressure or circulation?
On the Vaillant ecoTEC plus, the manufacturer's table has 6 water pressure or circulation codes: F.22, F.23, F.73, F.74, F.75, F.83. For F.22, F.73, F.75, first check the pressure gauge when cold and top up if low, as your user guide shows, then reset once. The others need a Gas Safe registered engineer.
Code still showing? Book a repair
CombiCert Ltd is a Gas Safe registered business (621146) in Telford, Shropshire. Our team of 2 to 5 engineers is led by director and Gas Safe engineer Peter Jefferson. Boiler repair from £90 + VAT, parts quoted separately.
Send us the make, model and the exact code on WhatsApp and we will tell you what we need to check.
Explanations are written by CombiCert from the manufacturer manuals listed, which you should check for your exact model. This page is general information, not a diagnosis. If you smell gas, call 0800 111 999.