Boiler installation

Boiler installation in England has to follow two sets of rules at once. A Gas Safe registered engineer must fit the boiler, and the Building Regulations set a minimum efficiency and a minimum set of controls for what goes in. A fitter who works to both will usually quote you for a boiler, controls, a flue, a system clean and a commissioning check as one package. This page explains gas boiler installation in plain terms: who may do the work, what the rules say, what shapes the price and how to compare firms. The standards below are for England. Wales, Scotland and Northern Ireland have their own versions, so ask the fitter which apply to you.

Who is allowed to fit a gas boiler

The Health and Safety Executive (HSE) says anyone employed to work on gas appliances in domestic premises must be a Gas Safe registered engineer, and that any installation or reinstallation counts as gas work. HSE also says the engineer must be competent in that particular type of work, which the back of their ID card shows. Check it before the fitter starts, and ask to see it again on the day. Our guide on how to check a plumber is Gas Safe registered lists the steps. HSE's domestic gas FAQ is the primary source.

A fitter who is also on a competent person scheme can tell your local council about the job for you. GOV.UK says boiler installers can self-certify their work and give you a certificate within 8 weeks of completion. Keep that certificate with your boiler's paperwork, as a buyer's solicitor may ask for it. Our guide on building regulations for plumbing and heating covers the wider picture.

What the rules say about the boiler you can fit

In England, the Building Regulations guidance in Approved Document L, Volume 1 sets a minimum efficiency of 92% (ErP) for a gas boiler serving radiators or underfloor heating in an existing home. The document allows a lower figure, 78% for natural gas, only in exceptional circumstances, which it defines by reference to the ODPM's condensing boiler installation assessment guide. In practice, that points most homes towards a condensing boiler.

The same document ties controls to the boiler. When a boiler is replaced, it says:

• each room, or each heating zone where that is justified, should have thermostatic room controls;
• the boiler controls should meet the standards in its Section 6 for the heating system;
• a boiler interlock should be fitted, and hot water and space heating should have separate time controls unless one controller already ran both;
• any accessible pipework in the home should be insulated.

If the new boiler is a gas combination boiler, at least one extra efficiency measure is needed. The choices are flue gas heat recovery, weather compensation, load compensation or a smart thermostat with automation and optimisation. This stems from the Boiler Plus standard, which the government's own FAQ says applied from April 2018 whenever a boiler is installed in an existing heating system in England. That FAQ also says the 92% requirement applies to the boiler as a product, so a lower-rated boiler cannot be brought up to standard by adding controls.

What a proper installation includes

Ask any firm to describe the steps, because a thorough job covers more than swapping the case on the wall.

1. Survey. The fitter looks at the old boiler, the flue route, the gas pipe, the condensate drain, the cylinder if there is one and the radiators. Boiler size should come from your home's heat needs, not from the size of the old unit.
2. Choice of type. Combi boilers heat water on demand and need no tank. System and regular boilers work with a hot water cylinder, which suits homes using several bathrooms at once. A good fitter explains why they recommend one over another.
3. Removal and fitting. The old boiler is disconnected and removed, the new one is mounted, and the gas, water, flue, condensate and electrical connections are made.
4. Cleaning and protection. Approved Document L says all central heating circuits should be thoroughly cleaned and flushed before a new heating appliance goes in, with a suitable chemical inhibitor added to the primary circuit. It says systems should be commissioned to BS 7593. Many installers fit a magnetic filter as well. Our page on power flushing explains the heavier clean for older systems.
5. Commissioning. The fitter tests the boiler, controls and flue, balances the radiators, sets the controls and shows you how to use them. The Benchmark Commissioning Checklist mentioned in the Approved Document is one way to record that this was done.
6. Paperwork. You should receive the manufacturer's guarantee details, the Building Regulations compliance certificate and a handover on how to use the system.

What affects the price

We do not publish prices, because they vary by region, by home and by firm, and the figures we have seen elsewhere date quickly. The factors that move a quote are these:

Ask every firm for a written, itemised quote naming the boiler make and model, the controls, the flue kit, the system clean, the filter and the guarantee. Quotes that look different on the page are often quoting for different jobs, so compare like with like. Our boiler repair page is worth a read first if you are not yet sure that replacement is the right call.

Running costs and efficiency

The energy price cap limits the unit rates and standing charges suppliers can charge on default tariffs. Ofgem's page lists a national average gas unit rate of 7.97p per kWh and a standing charge of 29.68p a day for Direct Debit customers between 1 October and 31 December 2026, both including VAT. A more efficient boiler and better controls use less gas for the same heat, so they reduce what you pay per unit. How much you save depends on your home, how you heat it and the boiler you are replacing, so be wary of a firm that promises a single figure without looking at your house.

Heat pumps and the Boiler Upgrade Scheme

A new gas boiler is not the only option. GOV.UK lists Boiler Upgrade Scheme grants of £7,500 towards an air source or ground source heat pump and £5,000 towards a biomass boiler, with an extra £1,500 until March 2027 for off-gas homes heated by oil or LPG and £2,500 for an air-to-air heat pump. It says you cannot get a grant for a hybrid system that pairs a gas boiler with a heat pump, and that you can get one grant per property. The English Housing Survey reports 276,000 dwellings, 1% of the total, used a heat pump as their primary space heating system in 2023, so gas boilers remain the norm in English homes. If you are weighing the two, ask any firm you contact whether it fits heat pumps or only boilers, and check the scheme's current rules on GOV.UK before you commit.

Choosing a firm

Verified reviews are a better guide than a polished website, and they are the first thing we use to order firms, ahead of distance. Pick your town on our cities page to compare local engineers. Then ask each one:

1. Are you Gas Safe registered for the type of boiler you are quoting?
2. Which competent person scheme will you notify the work through?
3. Is the quote itemised, and does it include flushing, a filter and commissioning?
4. Who is the guarantee with, how long does it last and what does it need from me, such as an annual service?
5. How will you protect floors and furniture, and what happens to the old boiler?
6. What will you leave with me when the job is finished?

A fitter who answers these without fuss is usually one worth booking. Once the boiler is in, arrange a service each year, as HSE advises at least annual servicing for gas appliances. If you are a landlord, keep our page on gas safety certificates to hand.