If your boiler's not working or starts making strange noises, you'll want to know why - fast. Some boilers have an LCD screen that displays error codes to let you know what's gone wrong. But if you don't have one of those, read on to learn about the most common reasons for a boiler breakdown and what you can do about them.

Leaking boiler

If you find a leak, you’ll probably need to contact a Gas Safe Registered engineer. Here are the main reasons for a boiler leak:

  • Pressure relief valve – if your boiler pressure is too high, the pressure valve will pass water as a safety precaution. Find out more about high pressure in our boiler pressure article.
  • Temperature pressure relief valve – some boilers/systems have this type of valve. It works in a similar way to a pressure relief valve. If the temperature is too high or there’s a fault with the temperature valve it will pass water.
  • Corrosion – your boiler tank and pipes can corrode over time. Single parts can be replaced, but if the damage is widespread you may need to install a new boiler or have your pipework upgraded.
  • Badly installed pipework – if you’ve had a new boiler fitted, a leaking pipe could be a sign it isn’t installed properly. Get in touch with your boiler fitter to investigate.
  • Leaking pump – a leaking boiler pump may need to be replaced or resealed.

High or low boiler pressure

Your central heating system needs to be sealed and pressurised to work. If the pressure is too high or too low, your boiler can stop working. Our boiler pressure page has information about why this could happen and how you can fix it.

Noisy boiler

There are many reasons why boilers make noises like banging, gurgling or whistling. A small amount of noise is pretty normal. But if it’s constant or very loud it could mean there’s an underlying issue. If you’re at all unsure, get an engineer to investigate.

  • Air in your central heating system - try bleeding your radiators to release this.
  • Low water pressure – check your boiler pressure gauge and read our article about boiler pressure.
  • Faulty pump – your pump pushes water around the system. You’ll need an engineer to check if it’s faulty.
  • Limescale or sludge – debris and limescale can build up in your system, causing it to make noise as the water gets trapped and overheats. This can lead to further problems so it would need to be cleaned out by a professional.

Boiler not firing up

Here are a few of the potential reasons why your boiler may not be igniting. You can try solving some issues yourself, but for other problems, you’ll need to contact a Gas Safe Registered engineer.

Thermostat set too low or faulty

If the temperature in your house is above what you’ve set your thermostat at, your boiler won’t come on. Try turning it up a few degrees to see if that helps. It’s also possible that your thermostat is faulty.

Boiler timer has reset

If you’ve had a power cut, your boiler timer could reset to its default settings, so it won’t come on when you expect it to. Check your boiler to see if this is the case.

Fuse has tripped

An electrical issue or power cut could trip the fuse for your boiler. Check your fuses to see if this is what’s happened. You may need to get an electrician to investigate if it continues to happen.

There’s no gas

If you don’t have gas or can smell gas, call the emergency line on 0800 111 999. If you’ve got a Pay As You Go (prepayment) meter check to see if it’s run out of credit.

Pilot light’s gone out

You can see if your pilot light has gone out by checking the window on the front of your boiler. It’s simple to re-light – our video shows you how. Or check your user manual to find out what to do.

Boiler pressure too low or too high

Your boiler pressure dropping or rising beyond where it should be can cause your boiler to turn off for safety reasons. Take a look at our boiler pressure article to find out why this can happen and what you can do about it.

Frozen condensate pipe

The condensate pipe allows condensed water to drain from heating systems that use combination boilers. Sometimes this pipe is outside, so it’s vulnerable to freezing when the temperature drops. Watch our video to see how to un-freeze it.

Boiler pump not working

The boiler or central heating pump moves water around your heating system. If your heating is taking longer than usual to heat up or your boiler is making strange noises, a pump problem might be why. As the pump is located inside your boiler, it’s probably best to get a Gas Safe Registered engineer to take a look.

Worn out pump

A pump should last about 15 years but could be worn down if used a lot and you’ll need to get a replacement.

Pump has no power

If your pump has no power, the fuse in it may have gone. Or there may be loose connections in the system you’ll need to get checked by a professional.

Build-up of debris or sludge

Dirt and particles can build up in the pump and stop it working. You may need a power flush to clear out the system. Fitting a magnetic filter can also help. The pump propeller can also get blocked by debris. If this is the case, you’ll need to replace the pump.

Leaking pump

If the boiler pump corrodes, it can start leaking and you’ll need to get a replacement pump fitted.

Peace of mind in case things go wrong

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