It depends on the job. A straightforward swap of one boiler for a similar one in the same place can often be done in a day. Moving the boiler, changing the type of system or adding new pipework takes longer. A good installer will tell you the likely time after a survey, not before.
Typical timescales
These are rough guides, not promises. Every house is different.
- Like-for-like replacement: often about one day, sometimes into a second if the system needs extra work.
- Changing from a regular boiler to a combi: commonly two to three days, because the tanks and cylinder come out and the pipework changes.
- Moving the boiler to a new position: around two to three days, depending on new pipework, flue and making good.
- Oil boiler replacement: similar to gas, with extra time if the tank, oil line or flue also need work.
- Adding a power flush or a new filter: adds time, often half a day to a day.
What takes the time
- Draining and removing the old boiler. Old pipework and fittings are sometimes in worse condition than expected.
- The flue. If the old flue cannot be reused, a new one means cutting through a wall or roof.
- Flushing the system. Cleaning the pipework and radiators before connecting the new boiler protects it, and takes time.
- Controls. Fitting a new thermostat or smart controls adds to the job.
- Commissioning. The boiler has to be filled, tested, set up and checked for safe combustion. We do not rush this.
- Surprises. Hidden leaks, old fittings, or in older houses materials that need special handling.
What a typical day looks like
On the day, the engineer protects your floors, isolates the system and drains it down, then removes the old boiler. The new one is mounted, the pipework and flue connected, a filter fitted, and the system refilled and flushed. Controls are connected, the boiler is commissioned and tested, and the engineer walks you through how it works.
Our guide on what to expect during your boiler installation takes you through it step by step.
How to help it go smoothly
- Clear the area around the old boiler and the route to it.
- Make sure there is parking nearby.
- Tell us about pets and access, and about anyone in the house who needs heating or hot water at specific times.
- Agree the position and any changes at the survey, not on the day.
Heating off for how long?
For a like-for-like swap, you are usually without heating and hot water for part of the day, and back in business that evening. Where the job is bigger, we agree arrangements with you in advance.
Ask for a free survey and quote and we will tell you how long yours should take. See also our boiler installation page.
