Central Heating Installation: What to Expect From Start to Finish

Stage one: the survey

A good installer spends time walking round the property before quoting. They measure rooms, note window sizes and wall types, look at loft and floor insulation, and ask how many people live there and how much hot water you use. Those details feed a heat-loss calculation, which tells the engineer how much heat each room loses on a cold day and therefore how large each radiator needs to be.

The survey is also where decisions get made about boiler type and position, where the flue can legally exit, whether the gas supply pipe is large enough and how the condensate pipe will be drained. If a quote arrives without anyone having looked in your airing cupboard or loft, treat it with caution.

Stage two: designing the system

From the survey the engineer chooses between a combination boiler, a system boiler with an unvented cylinder, or a regular boiler with tanks in the loft. Homes with one bathroom and modest hot water demand often suit a combi, while larger households running two showers at once usually do better with stored hot water.

Pipe routes are planned at this point too. The aim is the shortest sensible runs with as little disruption to finished floors and decoration as possible. Radiator positions are normally under windows, where they counter cold downdraughts, but that can change to suit furniture or kitchen layouts.

Stage three: first fix

First fix is when copper or plastic pipework is run from the boiler position to every radiator location. Carpets are rolled back, floorboards lifted, and in some rooms holes are drilled through joists or walls. This is the dustiest part of the project and the one that needs most preparation from you.

Clearing rooms, emptying the airing cupboard and moving anything fragile away from skirting boards makes the day go far more smoothly. Pets are usually happier elsewhere while boards are up.

Stage four: second fix

Second fix covers hanging radiators on brackets, fitting valves, connecting the boiler, installing the flue, and wiring the controls: a programmer or smart thermostat, plus thermostatic radiator valves in most rooms. Floorboards go back down once the pipework has been pressure tested and found tight.

Stage five: filling, flushing and commissioning

Before the new boiler runs for real, the system is filled, bled of air and cleaned so that flux and debris from installation do not end up in the heat exchanger. A chemical inhibitor is then added to protect the metal from corrosion. The engineer balances the radiators so the far rooms heat as quickly as the near ones, sets the boiler up for your system and checks gas pressures and flue readings.

You should be shown how to use the controls, told where the stopcock and isolation valves are, and given the commissioning checklist and warranty registration. Keep these together; manufacturers typically ask for them if you ever need to make a claim.

How long a full installation takes

There is no single figure because every house is different, but a whole-house installation in an average family home is a job measured in days, not hours. A bungalow with easy floor voids is quicker than a three-storey Victorian house with solid floors downstairs. Your engineer should give you a realistic timetable and tell you which days you will be without heating or hot water, so you can plan around them.

Frequently asked questions

Can I stay at home during a central heating installation?

Yes, most families do. Expect lifted floorboards, some dust and periods without heating or hot water, so it helps to plan meals and showers around the busiest days.

Do I need new radiators if I am only replacing the boiler?

Not necessarily. Existing radiators can often be reused if they are in good condition and correctly sized, although the system should be cleaned before a new boiler is connected.

Which boiler type should I choose?

It depends on the size of the house and how much hot water you use at once. A survey is the only reliable way to decide between a combi, system or regular boiler.

Is a smart thermostat worth adding?

For many households, yes. Room-by-room control and scheduling help avoid heating empty rooms, and they are easiest to fit while the system is already being installed.