In short
A straightforward like-for-like boiler swap in the same position is usually done in a day. Converting from a tank-fed system to a combi, moving the boiler or upgrading the gas pipe usually takes two days or more. Your installer should confirm the timescale after the survey, before work starts.
What decides how long it takes?
The boiler itself takes a few hours to hang and connect. The time goes on everything around it: draining and cleaning the system, the flue, the gas and condensate pipes, controls and testing. The more of those that change, the longer the job.
Typical timescales
- Like-for-like swap, same position: usually one day.
- Combi to combi with a new flue or controls: usually one day, sometimes a little longer.
- Regular or system boiler converted to a combi: usually two days or more, because the cylinder and loft tanks come out and pipework is altered.
- Moving the boiler to another room or the loft: usually two days or more, with new pipe runs and making good.
- Gas pipe upgrade: adds time if the existing pipe is too small for the new boiler.
What happens on installation day?
- The engineer protects floors and the work area and isolates gas, water and power.
- The old boiler is drained down and removed.
- The system is cleaned and flushed, and a filter fitted, ready for the new boiler.
- The new boiler, flue and condensate pipe are fitted and connected.
- The system is refilled, treated with inhibitor and checked for leaks.
- The gas supply is tested, and the boiler is commissioned: gas rate, combustion and safety checks.
- You are shown how to use the boiler and controls, and given the paperwork.
Will I have heating and hot water during the work?
Expect to be without heating and hot water while the old boiler is out, usually for most of the working day on a straight swap. On longer jobs, ask your installer how they will keep you going overnight. If you can choose, planning a replacement in late spring or summer is easier to live with than a winter breakdown.
How can I help the day go smoothly?
- Clear the area around the boiler and the route to it, including loft access if needed.
- Tell the installer about parking and anything they should know about the house.
- Keep children and pets away from the work area.
- Have your old boiler paperwork handy if you have it.
What CombiCert would check
After seeing the flue route, gas and water connections, condensate run and any extras (filter, flush, controls, moving the boiler), we confirm how many days the install should take and what you need to prepare. A straightforward like-for-like swap is usually one day; extras add time.
When to call a Gas Safe engineer
Installation and commissioning must be done by a Gas Safe registered engineer, and the work notified under the Building Regulations. After the install, if you notice a gas smell, a fault code or water leaking, stop using the boiler and call the installer. See also comparing boiler quotes and new boiler questions.
Need a hand? CombiCert in Telford
CombiCert Ltd is a Gas Safe registered (621146) gas and heating company based at The Old School House, Park Lane, Telford TF3 4TG, working across Telford and Shropshire for homes and businesses. We are open Monday to Saturday, 08:00 to 19:45 (closed Sunday).
New boilers from £1,750 inc VAT for a basic like-for-like installation, subject to a site inspection. Most quotes are higher; filters, flushes, thermostats and moving the boiler are paid extras.
See New boiler installation in Telford, or call or WhatsApp 07393 220694, or email hello@combicert.co.uk.
We cover Telford and nearby, including Wellington, Madeley, Dawley, Oakengates, Shifnal, Newport, Ironbridge and Shrewsbury.
Sources
Frequently asked questions
Can a combi boiler be replaced in one day?
Usually, yes, when it is a like-for-like swap in the same position and the gas pipe, flue route and condensate are suitable. Extra work, such as a new flue position, a gas pipe upgrade or moving the boiler, can add time. Your installer should confirm the timescale after looking at your home.
How long does a conversion to a combi take?
Converting from a regular or system boiler to a combi usually takes two days or more. The cylinder and any loft tanks are removed, pipework is altered so the combi takes water from the mains, and the system is cleaned and tested. The exact time depends on the house and how much pipework changes.
Do I need to be home during a boiler installation?
Someone should be there to let the engineer in, agree where things go and be shown the new controls at the end. You do not need to stay in the room all day. Make sure there is clear access to the boiler, the gas meter and the loft if the work involves it.
What should happen at the end of a boiler installation?
The engineer should test the gas supply, commission the boiler, check for leaks, show you how to use the boiler and controls, and leave the commissioning checklist and instructions. The warranty should be registered and the work notified so you receive a Building Regulations compliance certificate.
This answer is general information, not a substitute for an on-site assessment by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.