Can You Buy Your Own Boiler and Have It Fitted?

Yes, you can buy your own boiler and have it fitted. Boilers are sold to the public by plumbers' merchants, online retailers and some DIY stores, and there is no rule that the installer has to supply the boiler. What the law does require is that the installation is done by a Gas Safe registered engineer. The catch is everything around the boiler: the right output, the right flue kit, the controls, the warranty and who is responsible if the boiler turns out to be faulty. Those are where a customer-supplied boiler tends to lose the money it was meant to save.

Is it legal to buy a boiler and hand it to an installer?

Yes. Buying the appliance is not restricted. Fitting it is. Under the gas safety regulations, any work on a gas boiler, including connecting a new one, must be done by a Gas Safe registered engineer, and the installation has to be notified under Building Regulations. The engineer who fits it normally does that notification through the Gas Safe scheme and completes the Benchmark checklist, whoever paid for the boiler. So buying it yourself changes who chose the appliance. It does not change any of the rules about who installs it or the paperwork at the end.

Some merchants only sell to trade account holders, and some manufacturers put conditions on their longest warranties that depend on how the boiler was bought and who fitted it. Neither makes it illegal to buy one yourself. They just affect what you get with it.

Will an installer fit a boiler you have bought?

Some will and many will not, and the ones that will usually price it differently. There are good reasons for that, and it helps to understand them before you buy.

• They have not surveyed the house. If the boiler you bought is the wrong type or size, the installer either fits something they would not have recommended or has to tell you to send it back.
• They carry the liability for a product they did not choose. If the boiler fails in the first weeks, the question of whether it was the appliance or the installation lands on them.
• They cannot always offer their own backed warranty. Installers accredited with a manufacturer can often register extended cover on boilers they supply. That may not be available on one you bought elsewhere.
• Parts are part of how the job is priced. Take the boiler out of the quote and the labour line often goes up to compensate.

An installer who agrees to fit a customer-supplied boiler will normally guarantee their own workmanship only, not the appliance.

What goes wrong when the boiler is bought before the survey

The most common problem is buying the boiler before anyone has looked at the house. A boiler is not a single product you can pick off a shelf and plug in. These are the mistakes that come up most:

• Wrong output. Buying the biggest combi in a range "to be safe" gives a boiler that cycles on and off and wastes gas. Buying one too small leaves weak hot water. Output should come from the house and the hot water demand, which is what the boiler sizing guide walks through.
• Wrong type. A combi bought for a house with two bathrooms in use every morning, or a system boiler bought for a flat with no room for a cylinder.
• Wrong or missing flue parts. The boiler usually comes with a standard horizontal flue. If the flue has to go up through a roof, needs extensions, or needs a plume kit to meet positioning rules, those are extra parts that have to match the boiler.
• Controls that do not meet the rules. In England, a combi replacement must meet the Boiler Plus requirements for controls. A basic boiler with nothing else does not.
• No filter or system clean. Manufacturers usually expect a cleaned system and a magnetic filter for the warranty to hold. These are easy to leave off a DIY shopping list.
• The gas pipe. A modern combi can need a larger gas supply pipe than the old boiler had. That is found at survey, not at checkout.

Any of these can mean a second trip to the merchant, a boiler returned at your cost, or an installation that goes ahead with compromises.

What happens to the warranty

The manufacturer's warranty belongs to the boiler, so a customer-supplied boiler still has one. The question is how long and on what conditions. The longest warranties are usually tied to installation by an installer accredited with that manufacturer, registration within a set period after fitting, a filter, and an annual service. If your installer is not accredited with the brand you bought, you may be entitled only to the standard term, not the extended one advertised.

Then there is the grey area. If a new boiler develops a fault in its first month, the manufacturer may send an engineer who finds the boiler is fine and the problem is the installation, or the installer may say the installation is fine and the problem is the boiler. When the installer supplied the boiler, that argument is theirs to sort out. When you supplied it, you can end up in the middle. Our guide to the Benchmark checklist explains the paperwork that protects your cover either way.

Is it actually cheaper?

Sometimes, but usually by less than the difference between the online boiler price and a supply-and-fit quote suggests. Installers buy boilers at trade prices, so their parts cost is not the retail figure you see online. Once you add the flue parts, filter, controls and any fittings you did not know you needed, and allow for a labour rate that may be higher on a customer-supplied job, the gap often narrows a lot. If the installer cannot offer an extended warranty on your boiler, you may also have traded a modest saving for several years of cover.

A cheap boiler and installation can be perfectly good value when it is a like-for-like swap and every item is written down. The way to find out is to compare full quotes on the same basis rather than a boiler price against a quote. Comparing boiler quotes line by line shows how.

When buying your own boiler makes sense

It can work when the thinking has already been done. For example:

• An installer has surveyed the house, named the exact model, output and flue kit, and agreed in writing to fit a boiler you source.
• You are doing a larger renovation and your builder buys materials on a trade account, with the heating engineer's parts list to work from.
• It is a straight like-for-like replacement of a current model, in the same position, with the same flue.

It is the wrong answer when you are buying the boiler first and hoping to find someone to fit it, when you are not sure whether you need a combi or a system boiler, or when the main reason is a boiler that looked cheap online. Second-hand and reconditioned boilers are a particularly poor bet: no manufacturer warranty, unknown history, and most installers will decline to fit them.

The simpler route

If you want to control the cost, a survey first costs you nothing and tells you exactly which boiler, output and parts the house needs. You can then compare supply-and-fit quotes on the same specification, or price the boiler yourself if you still want to. Our survey is free, the quote names the boiler and lists what is and is not included, and it is fixed in writing. Book a free survey before you buy anything.