Should I repair or replace my boiler?

The usual rule of thumb: if the repair costs more than a third of a new boiler and the boiler is over eight years old, replace it. If it is under five years old and still in warranty, repair it. Between those two, it depends on which part has failed.

Which part has broken matters more than the age

Some failures are routine and cheap. Others are the boiler telling you it is finished.

• Thermostat, pressure sensor, or a leaking valve: among the cheapest repairs there are. Worth fixing at almost any age.
• Diverter valve: a routine mid-life repair. Common on combis around the 8 to 10 year mark. Usually worth fixing once.
• Pump: dearer than a valve, still a normal repair. Worth fixing unless the boiler is already past ten.
• Printed circuit board: one of the most expensive parts on the boiler. On an older boiler this is the point to think hard.
• Heat exchanger: the most expensive single component, and a large fraction of what a whole new boiler costs. On anything over eight years old, this is usually the end. Its failure often means the system water has been damaging the boiler for years.

The questions that actually decide it

Age is the first one, but not the only one. Work through these honestly:

• How old is it? Most gas boilers last 10 to 15 years with annual servicing. Past 15, spending a significant sum on a repair is renting time.
• Is it still under warranty? If yes, repair it, and make sure the annual services have been logged or the claim may be refused.
• How many times has it broken in two years? Two or more separate faults is a pattern, not bad luck.
• Are parts still available? Manufacturers discontinue parts for older models, and an obsolete part means the next fault is terminal regardless.
• What is it costing you to run? An old non-condensing boiler wastes a meaningful share of the gas you pay for.

What replacing actually saves

Households replacing an old, inefficient boiler with a modern condensing model can save up to around £840 a year, according to Energy Saving Trust figures. The saving is largest on older, larger, less efficient properties and smallest when the boiler you are replacing is already fairly modern.

Set that against the repair. A large repair bill on a fourteen-year-old boiler that is also wasting gas every winter is a worse deal than it looks on the day. The rough test: if the repair is a large fraction of what a replacement would cost, replacing usually wins.

Source: Energy Saving Trust

The one situation where you should always replace

If a Gas Safe registered engineer condemns the boiler as immediately dangerous or at risk, it comes off. That is not a negotiation and no reputable engineer will reconnect it.

If you smell gas, call the National Gas Emergency Service on 0800 111 999 immediately, turn off the supply at the meter if you can reach it safely, open windows, and do not touch electrical switches.

Source: Gas Safe Register

What an annual service actually does for the decision

A serviced boiler tells you more than an unserviced one. The engineer records the gas pressure, checks the flue gases and the seals, and notes anything starting to fail. Three years of service records turn the repair-or-replace question from a guess into a trend.

It also matters commercially: most manufacturer warranties require an annual service by a Gas Safe registered engineer with the paperwork retained. Skipping services to save a modest amount each year is a false economy if it invalidates cover on the heat exchanger, which is the dearest part in the boiler.

The false economy nobody warns you about

Repairing repeatedly is how people end up spending more than a new boiler without ever making a decision. A diverter valve one winter, a pressure sensor eight months later, a pump the winter after: three ordinary repairs in two years add up to a serious fraction of a replacement, on a boiler that is still fifteen years old and still inefficient.

The trap is that each individual repair looks cheaper than replacing. Add them up across two years before you agree to the third one.

Is it worth replacing a boiler that still works?

Sometimes, and the honest answer depends on what it is costing you to run rather than on whether it fires up.

An old non-condensing boiler wastes a meaningful share of the gas it burns. If yours is over fifteen years old, the annual waste can be substantial in a larger property, and that is money gone every year regardless of whether anything breaks. If it is ten years old and condensing, the case is much weaker and you are better off waiting.

The other consideration is timing. Replacing on your own schedule, in summer, with three quotes, costs less and is far less stressful than replacing in an emergency.

If you are on the fence

Get the repair quote and a replacement quote at the same time, then compare them properly. Most people only get one and decide in the dark, usually in January, with no heating, which is the worst possible moment to make a four-figure decision.