Common questions about Glow-worm 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.
Glow-worm Energy7 combi (25c / 30c / 35c-A)
Glow-worm boilers show F. followed by a number, e.g. F.28, the same style as Vaillant (both are made by the Vaillant Group).
Source: Glow-worm Energy7 Installation and Maintenance Instructions, doc. 0020300875_01, PDF pp. 51–53, Appendix E Overview of fault codes. Open the manual (PDF) (Manufacturer copy)
Ignition / flame
F.27 Glow-worm Energy7
Engineer after one resetIgnition / flameWhat it means
Safety shut-down: fault in flame detection (a flame is detected when there should be none).
Likely causes
Moisture on the electronics, a faulty flame monitor or a leaking 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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.27 is a safety shut-down: fault in flame detection (a flame is detected when there should be none). 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 Glow-worm Energy7
Engineer after one resetIgnition / flameWhat it means
Ignition unsuccessful when starting.
Likely causes
Gas supply off or low, air in the gas, a frozen or blocked condensate pipe, the gas valve, ignition parts or earthing.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.28 is listed in the manufacturer's table as "Ignition unsuccessful when starting". 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 Glow-worm Energy7
Safe checks firstIgnition / flameWhat it means
Flame loss during operation.
Likely causes
Gas supply interrupted, flue gas recirculation, poor earthing or ignition spark failure.
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.29 mean on a Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.29 is listed in the manufacturer's table as "Flame loss during operation". Likely causes include gas supply interrupted, flue gas recirculation, poor earthing or ignition spark failure. 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 Glow-worm Energy7
Engineer after one resetIgnition / flameWhat it means
Gas valve assembly control fault.
Likely causes
A short in the gas valve harness, or a faulty gas valve or electronics.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.61 is listed in the manufacturer's table as "Gas valve assembly control 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.62 Glow-worm Energy7
Engineer after one resetIgnition / flameWhat it means
Gas valve switch-off control fault: the valve shuts off late.
Likely causes
Delayed gas valve shut-off or delayed flame extinguishing.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.62 is listed in the manufacturer's table as "Gas valve switch-off control fault: the valve shuts off late". 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 Glow-worm Energy7
Engineer after one resetIgnition / flameWhat it means
Implausible flame signal returned to the electronics.
Likely causes
Flame signal fault or electronics defective.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.67 is listed in the manufacturer's table as "Implausible flame signal returned to the electronics". Likely causes include flame signal fault or electronics defective. 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 Glow-worm Energy7
Engineer after one resetIgnition / flameWhat it means
Unstable flame signal.
Likely causes
Air in the gas, low gas pressure, incorrect air ratio or a condensate route problem.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, 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.87 Glow-worm Energy7
Engineer after one resetIgnition / flameWhat it means
Electrode fault: electrodes not connected, connected wrongly or shorted.
Likely causes
Electrode connections or harness.
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.87 mean on a Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.87 is listed in the manufacturer's table as "Electrode fault: electrodes not connected, connected wrongly or shorted". Likely causes include electrode connections or harness. 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.88 Glow-worm Energy7
Engineer after one resetIgnition / flameWhat it means
Gas valve assembly not connected, connected wrongly or shorted.
Likely causes
Gas valve connections or harness.
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.88 mean on a Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.88 is listed in the manufacturer's table as "Gas valve assembly not connected, connected wrongly or shorted". Likely causes include gas valve connections or harness. 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 Glow-worm Energy7
Safe checks firstWater pressure / circulationWhat it means
Safety shut-down: not enough water in the boiler (low pressure).
Likely causes
Low system pressure, the water pressure sensor, or pump/sensor 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.22 mean on a Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.22 is a safety shut-down: not enough water in the boiler (low 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 Glow-worm Energy7
Engineer after one resetWater pressure / circulationWhat it means
Safety shut-down: the flow/return temperature difference is too large.
Likely causes
Pump blocked or weak, air in the boiler, or flow and return sensors swapped.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.23 is a safety shut-down: the flow/return temperature difference is too large. Likely causes include pump blocked or weak, air in the boiler, or flow and return sensors swapped. 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 Glow-worm Energy7
Engineer after one resetWater pressure / circulationWhat it means
Water pressure sensor not connected or short circuited.
Likely causes
Pressure sensor or its 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 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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.73 is listed in the manufacturer's table as "Water pressure sensor not connected or short circuited". Likely causes include pressure sensor or its wiring. 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 Glow-worm Energy7
Engineer after one resetWater pressure / circulationWhat it means
Pressure sensor fault: no pressure rise seen when the pump starts.
Likely causes
Pressure switch or sensor defective, or air or low water in the system.
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.75 mean on a Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.75 is listed in the manufacturer's table as "Pressure sensor fault: no pressure rise seen when the pump starts". Reset once; if the code comes back, book a Gas Safe registered engineer and quote the full code. Do not open the casing.
F.83 Glow-worm Energy7
Engineer after one resetWater pressure / circulationWhat it means
Dry fire: little or no temperature change at the flow or return sensor when the burner starts.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.83 is listed in the manufacturer's table as "Dry fire: little or no temperature change at the flow or return sensor when the burner starts". Reset once; if the code comes back, book a Gas Safe registered engineer and quote the full code. Do not open the casing.
F.89 Glow-worm Energy7
Engineer after one resetWater pressure / circulationWhat it means
Pump not connected or connected wrongly.
Likely causes
Pump wiring or pump type.
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.89 mean on a Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.89 is listed in the manufacturer's table as "Pump not connected or connected wrongly". Likely causes include pump wiring or pump type. 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 Glow-worm Energy7
Engineer after one resetTemperature / overheatWhat it means
Safety shut-down: overheating temperature reached.
Likely causes
Poor earth between harness and boiler, sensor problems, or poor circulation.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.20 is a safety shut-down: overheating temperature reached. Likely causes include poor earth between harness and boiler, sensor problems, or poor circulation. 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 Glow-worm Energy7
Engineer after one resetTemperature / overheatWhat it means
Safety shut-down: the temperature rose too fast.
Likely causes
Pump blocked or weak, air in the boiler, low system pressure.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.24 is a safety shut-down: the temperature rose too fast. Likely causes include pump blocked or weak, air in the boiler, low system pressure. 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 Glow-worm Energy7
Engineer after one resetFlue / fan / airWhat it means
Safety shut-down: flue gas temperature too high.
Likely causes
Break in the flue safety cut-out connection or harness.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.25 is a safety shut-down: flue gas temperature too high. Likely causes include break in the flue safety cut-out connection or harness. 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 Glow-worm Energy7
Engineer after one resetFlue / fan / airWhat it means
Fan fault (the manual also notes the fan frost protection function).
Likely causes
Fan plug or harness, a blocked fan, the Hall sensor or electronics.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.32 is listed in the manufacturer's table as "Fan fault (the manual also notes the fan frost protection function)". 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 Glow-worm Energy7
Engineer after one resetSensors / thermistorsWhat it means
Flow temperature sensor fault (open circuit).
Likely causes
Loose or unplugged sensor plug, harness break or failed 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.00 mean on a Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.00 is listed in the manufacturer's table as "Flow temperature sensor fault (open circuit)". Likely causes include loose or unplugged sensor plug, harness break or failed 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.01 Glow-worm Energy7
Engineer after one resetSensors / thermistorsWhat it means
Return temperature sensor fault (open circuit).
Likely causes
Loose or unplugged sensor plug, harness break or failed 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.01 mean on a Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.01 is listed in the manufacturer's table as "Return temperature sensor fault (open circuit)". Likely causes include loose or unplugged sensor plug, harness break or failed 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.10 Glow-worm Energy7
Engineer after one resetSensors / thermistorsWhat it means
Flow temperature sensor short circuit.
Likely causes
Failed sensor or a short in the harness.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.10 is listed in the manufacturer's table as "Flow temperature sensor short circuit". Likely causes include failed sensor or a short in the harness. 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 Glow-worm Energy7
Engineer after one resetSensors / thermistorsWhat it means
Return temperature sensor short circuit.
Likely causes
Failed sensor or a short in the harness.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.11 is listed in the manufacturer's table as "Return temperature sensor short circuit". Likely causes include failed sensor or a short in the harness. 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 Glow-worm Energy7
Engineer after one resetSensors / thermistorsWhat it means
Flow or return temperature sensor stuck at a constant value.
Likely causes
Faulty flow 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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.71 is listed in the manufacturer's table as "Flow or return temperature sensor stuck at a constant value". Likely causes include faulty flow 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.
PCB / electrical
F.49 Glow-worm Energy7
Engineer after one resetPCB / electricalWhat it means
eBUS fault: voltage too low.
Likely causes
A short or overload on the eBUS, or two supplies with different polarity.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.49 is listed in the manufacturer's table as "eBUS fault: voltage too low". 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 Glow-worm Energy7
Engineer after one resetPCB / electricalWhat it means
EEPROM fault.
Likely causes
Electronics defective.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.63 is listed in the manufacturer's table as "EEPROM fault". Likely causes include electronics defective. 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 Glow-worm Energy7
Engineer after one resetPCB / electricalWhat it means
Electronics, sensor or analogue-to-digital converter fault.
Likely causes
Flow or return sensor short circuit, or electronics defective.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.64 is listed in the manufacturer's table as "Electronics, sensor or analogue-to-digital converter fault". Likely causes include flow or return sensor short circuit, or electronics defective. 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 Glow-worm Energy7
Engineer after one resetPCB / electricalWhat it means
Electronics temperature too high.
Likely causes
Overheating electronics due to external heat, or electronics defective.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.65 is listed in the manufacturer's table as "Electronics temperature too high". Likely causes include overheating electronics due to external heat, or electronics defective. 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 Glow-worm Energy7
Engineer after one resetPCB / electricalWhat it means
Invalid product code (DSN).
Likely causes
Display and board replaced at the same time without the code being set.
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 Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.70 is listed in the manufacturer's table as "Invalid product code (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.
F.97 Glow-worm Energy7
Engineer after one resetPCB / electricalWhat it means
Main PCB self-test failed.
Likely causes
Main PCB defective.
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.97 mean on a Glow-worm Energy7 combi boiler?
On a Glow-worm Energy7 combi, F.97 means the main PCB self-test failed. Likely causes include main PCB defective. 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 Glow-worm fault codes
2 questions
Which Glow-worm fault codes can I usually deal with myself?
On the Glow-worm ranges in our guide, only these codes have a safe homeowner check first: F.29 for gas supply or flame loss (check the meter and credit); F.22 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 Glow-worm Energy7 combi?
Glow-worm publishes the fault table in the installation and servicing manual for the Energy7 combi (0020300875_01, PDF pp. 51–53). CombiCert's fault code guide explains 30 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: Glow-worm Energy7 combi (25c / 30c / 35c-A)
6 questions
Which Glow-worm Energy7 combi fault codes relate to the flue, fan or air supply?
On the Glow-worm Energy7 combi, 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 Glow-worm Energy7 combi fault codes mean the boiler will not light or loses its flame?
On the Glow-worm Energy7 combi, the manufacturer's table has 9 ignition or flame codes: F.27, F.28, F.29, F.61, F.62, F.67, F.68, F.87, F.88. For F.29, first check the gas meter, prepay credit and another gas appliance, then reset once. The others need a Gas Safe registered engineer.
Which Glow-worm Energy7 combi fault codes point to a control board or electrical fault?
On the Glow-worm Energy7 combi, the manufacturer's table has 6 control board or electrical codes: F.49, F.63, F.64, F.65, F.70, F.97. 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 Glow-worm Energy7 combi fault codes point to a temperature sensor fault?
On the Glow-worm Energy7 combi, the manufacturer's table has 5 temperature sensor codes: F.00, F.01, F.10, F.11, F.71. 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 Glow-worm Energy7 combi fault codes mean the boiler is overheating?
On the Glow-worm Energy7 combi, 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 Glow-worm Energy7 combi fault codes relate to water pressure or circulation?
On the Glow-worm Energy7 combi, the manufacturer's table has 6 water pressure or circulation codes: F.22, F.23, F.73, F.75, F.83, F.89. For F.22, 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.