Boiler repair

A boiler that has stopped working is usually fixable in one visit, but only a Gas Safe registered engineer may open up a gas boiler and work on it. Before you call, there are a few checks you can do yourself with no tools. If you smell gas, or think fumes are escaping, skip the checks and follow the emergency steps in the next section. This page covers gas boiler repair for homes in the UK. It also touches on electric boilers, which have no gas supply or flue. Your last step is to compare local engineers through our city pages, where firms are ordered by verified reviews first and distance second, never by payment.

If you smell gas or suspect fumes

Treat these as emergencies. The Health and Safety Executive (HSE) says to call the National Gas Emergency Service on 0800 111 999, switch off the appliance, turn the gas off at the meter control valve and open doors and windows. It also says to see your GP and mention possible carbon monoxide exposure. HSE's carbon monoxide guidance lists warning signs on or near an appliance: flames that burn yellow or orange rather than blue, soot or yellow-brown staining, a pilot light that keeps going out, and more condensation than usual inside windows.

HSE adds that it is illegal to use a gas appliance you suspect is unsafe. Leave it off until a Gas Safe registered engineer has checked it. For anything that cannot wait for a normal appointment, see our page on emergency plumbers.

Checks worth doing before you call

Most call-outs start with a handful of causes. Going through this list takes ten minutes and sometimes saves the visit.

1. Power and settings. Check the boiler has power, the programmer is on, the room thermostat is calling for heat and any thermostatic radiator valves are open.
2. Pressure. Many boilers have a gauge on the front. If it has dropped well below the range in your manual, the boiler may lock out. Some can be topped up by following the manual, but if the pressure keeps falling there is a leak somewhere and an engineer should find it.
3. Display fault code. Write down the code and the make and model. It gives the engineer a head start and lets you search the manufacturer's own guide.
4. Frozen condensate pipe. In a hard frost, the plastic pipe that carries condensation outside can freeze and shut a condensing boiler down. Pouring warm, not boiling, water over the frozen section can clear it. If you are not sure which pipe it is, wait for the engineer.
5. Radiators cold at the top. Air trapped in a radiator can stop it heating fully, and bleeding it is a normal homeowner job. If every radiator is cold at the bottom, the problem is likely sludge or a circulation fault, which is a heating engineer's job. Our page on radiators and heating covers that side.

Do not remove the boiler casing, adjust gas pressure settings or try to repair a leaking joint on the gas line. Those tasks count as gas work.

What the engineer does on a repair visit

A repair visit is a diagnosis first. A good engineer asks when the fault started, whether it comes and goes and whether anything changed beforehand, such as a power cut or a new thermostat. They then check the supply, controls, ignition, pump, diverter valve, heat exchanger and flue, using the manufacturer's data for your model. They should test the appliance for safe operation once the fault is cured, and explain what they found in plain words.

Ask for the faulty part to be shown to you if it was replaced. Ask too whether the work changes anything about the warranty. If the boiler is still covered by the maker's warranty, the repair may need to be done by an approved engineer for that brand.

Repair or replace?

A one-off fault in a boiler that has otherwise worked well is usually worth repairing. Repeated call-outs for different faults, parts that are hard to find, or a heat exchanger or main circuit failure point towards replacement instead. Ask the engineer for a straight view and a written note of the fault, so you can compare a repair quote against a replacement quote. Our boiler installation page explains the rules a new boiler has to meet in England, and what comes with a new installation.

Gas boilers are everywhere, which is why engineers meet such a wide spread of ages and makes. The English Housing Survey reports around 21.2 million households, 86% of the total, using a gas-fired main heating system in 2023-24. By 2024 it found 63% of homes had a condensing-combination boiler, so many of the faults you will hear about involve that type.

What affects the cost of a repair

We do not list prices, because they vary by region and by fault, and any figure we quoted would soon be out of date. These are the factors that move a quote:

• The fault itself. A reset or a new sensor is a smaller job than a pump or a heat exchanger.
• The make and model. Parts for older or less common boilers can take longer to source.
• Call-out and labour terms. Some firms charge a call-out fee that includes the first hour, and others charge separately.
• Time of day. Out-of-hours and weekend visits are usually priced higher.
• Access. A boiler in a loft or a tight cupboard can take longer to work on.

Ask what is included before you agree, and ask for a written quote for anything beyond the first diagnosis. Registration with Gas Safe tells you about safety and competence, not about price, so compare quotes from more than one engineer when the job is not an emergency.

How to check the engineer before they start

Gas work in a home must be done by a Gas Safe registered engineer. HSE says engineers must also be competent in the specific type of work, and that the back of the ID card shows what each engineer is qualified to do. Ask to see the card before they start, check the back covers boilers, and confirm the details with Gas Safe Register on its freefone helpline, 0800 408 5500. Our guide on how to check a plumber is Gas Safe registered walks through it step by step.

Registration says an engineer is legally able to work on gas. It does not say how good they are. Verified reviews from real customers help here, which is why they come first in how we order firms. When you are choosing, ask:

1. Which makes do you work on most often?
2. Will you diagnose first and quote before replacing parts?
3. Do you carry common parts on the van?
4. What do you guarantee on parts and labour, and for how long?
5. Will you test the carbon monoxide levels and check the flue before you leave?

Service it, and fit a carbon monoxide alarm

HSE recommends that gas appliances, flues and pipework are serviced at least annually by a Gas Safe registered engineer. A service finds worn parts before they fail in the cold snap. It is also when an engineer checks combustion and the flue, which are the two things that matter most for carbon monoxide. HSE reports that around seven people die each year from CO poisoning caused by gas appliances and flues, and that alarms start at about £15 and should meet BS EN 50291. An alarm does not replace servicing, but it is a cheap second line of defence. If you rent out a property, your duties go further than this, and our guide to the landlord gas safety record sets them out, alongside our page on gas safety certificates.

Electric boilers

Electric boilers have no burner, gas supply or flue, so the carbon monoxide risks above do not apply in the same way. Gas Safe registration covers gas only, so ask for an electrician or heating engineer with training on that make. The same questions apply: ask about their experience with your model, a written quote, and what guarantee they give on the repair.

Where to look next

Pick your town on our cities page to see engineers listed by verified reviews, then distance. Check registration yourself before booking, and keep the invoice and any fault codes in a folder with your boiler manual.