Guide

How long does a boiler last? When to replace one

Most boilers last 10 to 15 years. Age alone is not a reason to replace one: a failed heat exchanger, parts no longer made, or a repair costing more than about a third of a new boiler are.

A new wall hung boiler with its flue and pipe tails, the old one taken out beside it

The typical lifespan

Boiler manufacturers put the usual life of a domestic gas boiler at 10 to 15 years. Some run well past twenty and some need replacing at eight, and the difference usually comes down to how the boiler was installed, how clean the water in the system is, and whether it has been serviced every year.

A boiler's age is printed on the data badge, usually under the front panel or on the side, and it is also on the Gas Safe building regulations certificate issued when it was fitted. If neither can be found, the model name searched online will give its production years.

What shortens a boiler's life

Dirty system water. Sludge from corroding radiators clogs the heat exchanger and wears the pump. A boiler fitted to an uncleaned system with no filter is starting its life at a disadvantage.
Hard water. In hard water areas, limescale builds up in the part of a combi that heats the tap water, and the boiler gets noisier and slower to deliver hot water.
No annual service. Seals, the condensate trap and the burner are all checked at a service. Faults found early stay small.
Oversizing. A boiler too powerful for the house fires, overshoots and shuts off repeatedly. That short cycling wears ignition parts and fans.
Incomplete commissioning. A boiler not set up against the manufacturer's gas rate and flue gas figures can run with the wrong mixture for years.

Signs it is near the end

Breakdowns becoming a yearly event rather than a rare one. An engineer telling you a part is obsolete or on long lead times. Water leaking from inside the casing, which on an older boiler often means the heat exchanger. Rising gas bills with no change in how you use the heating. And a boiler from before 2005 that is not a condensing model: since then, the building regulations in England and Wales have required new gas boilers to be condensing, with narrow exceptions, so an older non-condensing boiler is a generation behind on efficiency.

Repair or replace: the arithmetic

A useful rule is that a repair under about a third of the price of a replacement is usually worth doing, provided the boiler is otherwise sound and parts are available. Above that, or once the heat exchanger has failed on a boiler past fifteen years, replacement is usually the cheaper answer over the next five.

Work	Typical price
Annual service	£70 to £120
Diverter valve, pump or expansion vessel	£180 to £400
Printed circuit board	£300 to £600
Combi swap, same position	£1,900 to £3,600
Conventional to combi conversion	£3,200 to £5,500

Replacing before it fails has one clear advantage: you choose when. A boiler that stops working in January is replaced at the busiest time of year, when there is less choice of installer and date.

What a new boiler has to meet

In England, the Boiler Plus standard has applied since April 2018. A new gas boiler must have an efficiency of at least 92% on the ErP scale, and every gas and oil system needs a timer and a room thermostat. When a combi is fitted, the installer must also add one further energy saving measure: flue gas heat recovery, weather compensation, load compensation, or a smart thermostat with automation and optimisation.

The installation is notifiable building work, and a Gas Safe registered installer notifies it for you. The certificate that follows is worth keeping, because a buyer's solicitor will ask for it when you sell.

Warranties and what keeps them valid

New boiler warranties vary by manufacturer and often by installer, and the longer ones usually depend on the boiler being registered with the manufacturer soon after fitting and serviced every year by a Gas Safe registered engineer. The service record is the evidence. A missed year can void a warranty that had several years left to run, which is why the annual service on a boiler under warranty is better thought of as part of the purchase price than as an optional extra. Ask your installer who registers the warranty and keep the paperwork with the building regulations certificate.

Making the current one last

Book the annual service in late summer, when engineers have time and a fault is a booking rather than an emergency. Ask for the inhibitor level to be checked and the magnetic filter to be emptied at the same visit. If there is no filter, fitting one is the single cheapest thing that protects a boiler. And keep the pressure between 1 and 1.5 bar cold, because a boiler that runs repeatedly at low pressure locks out and wears its components faster.

Common questions

Is a 20 year old boiler dangerous?

Not because of its age. Safety depends on condition, and the faults that matter are a leaking flue, incomplete combustion or blocked ventilation. An annual service and a working carbon monoxide alarm in the room are what keep an old boiler safe.

Can I get a grant to replace a gas boiler?

Not through the Boiler Upgrade Scheme, which only funds heat pumps and biomass boilers. Other energy efficiency schemes open and close over time and are usually tied to income or benefits, so check what is open when you are ready to replace.

Does a new boiler need a power flush?

Manufacturers require the system to be cleaned, but on a system in good condition a chemical flush and a magnetic filter usually meet that requirement. A power flush is for systems already showing sludge.

How long does a boiler replacement take?

A like for like swap in the same position is usually one to two days. A conversion from a system with a cylinder and loft tanks to a combi is typically two to three.