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10 common boiler problems - what you can do about them

By James Baker | Posted September 15, 2021

Whether your pilot light keeps going out, your combi boiler is making a vibrating noise, or you're simply having trouble with a broken boiler, we're here to help. Learn how to diagnose common boiler issues and quickly restore your central heating system.

Your boiler is the heart of your home, so it’s important to keep it working efficiently for as long as possible.

Below, we list some of the most common boiler issues and outline their potential causes and their possible fixes:

  • The pilot light keeps going out

  • The boiler is making noises (Gurgling, whistling or banging)

  • No heating or hot water

  • Boiler is leaking

  • Low boiler pressure

  • Radiators are cold

  • Boiler is kettling

  • The boiler is not responding to the thermostat.

  • Frozen condensate pipe

  • The boiler keeps switching off

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1. Pilot light keeps going out

The pilot light is the small gas burner kept alight permanently on your boiler. The pilot light going out is a really common problem and could be caused by something as simple as a draught blowing the flame out or a build-up on the gas nozzle.

Alternatively, a broken thermocouple could be stopping the gas supply. The thermocouple is a safety device in the boiler that detects any temperature change in your pilot light so it knows if the pilot light goes out.

What you can do

Check that your other gas appliances are working. If they're not, contact your gas supplier. If your gas supply is okay, try reigniting the pilot light by following your boiler manufacturer's instruction manual. If you've lost the instructions, you can usually find them on the boiler manufacturer's website. This fault is more common with older boilers, as modern systems are not built with pilot lights and ignite electronically. If the issue with your pilot light persists, it may be worth getting a new boiler installed.

2. Boiler is making noises (gurgling, whistling or banging)

If your boiler is making vibrating, banging, gurgling or whistling noises, the most likely cause is air in the system. Low water pressure or a failing pump could also be the cause. If you hear a noise coming from the boiler or heating system, don't ignore it, as there's probably a fault. The potential fault will vary depending on the type of sound and where it's coming from. 

What you can do

If your boiler is humming or vibrating, adjust the settings or check the connectors. The noise could be a symptom of a more serious fault, so if you're not sure, make sure you contact your supplier.

Bleeding your radiators can help if the pipes are gurgling. However, a frozen condensate pipe can also cause a similar noise (see number nine below).

Knocking can be caused by the expansion and contraction of your heating pipes. This is normal, but it could be useful to check that the pipes aren't fixed to floorboards or joists too tightly.

3. No heating or hot water

Your boiler is a key part of your home, and you should be able to rely on it to help provide your home with heating and hot water. There are likely to be several causes for this fault – many of which will require a replacement part. 

What you can do

There is not usually one single issue that can lead to your boiler failing to provide heat or hot water. However, you should start by checking that there are no issues with your boiler's pressure or thermostat. If there are no issues, call an engineer to repair your boiler.

4. Boiler is leaking

Causes can vary, depending on where the leak or drip is coming from. A leaking system can result from a broken component, such as a seal or valve. It could also be the result of corrosion. 

What you can do

Call an engineer to repair your boiler. Never try to fix a faulty boiler yourself.

5. Low boiler pressure

If your boiler's pressure gauge shows a reading lower than one, you may have a problem.

What you can do

Check for leaks in the system. If you find a leak, call an engineer to repair your boiler immediately.

If there are no leaks, you can try re-pressurising the system by carefully following your boiler manufacturer's instruction manual. If there is still no improvement, you should call an engineer, as there's likely a failed component in the system.

6. Radiators are cold

If your radiators are only partially warm, or only some of them are working, the most likely reason for this is air in the central heating system.

What you can do

Bleed your radiators. If there's no improvement, the system might need flushing – this needs to be carried out by a professional central heating engineer.

7. Boiler is kettling

If your boiler sounds like a boiling kettle, a build-up of sludge or scaly material is probably restricting the water flow. This is a common problem in hard water areas.

What you can do

Call a registered professional engineer and get your system professionally flushed.

8. Boiler not responding to thermostat 

A faulty thermostat can sometimes cause problems in an otherwise healthy system.

What you can do

Check your thermostat. Sometimes, an accidental knock can switch off or change the thermostat's settings. If your thermostat settings seem okay, but the temperature is not, it could be time to replace your thermostat.

9. Frozen condensate pipe

If you have a condensing boiler, it has a pipe that carries condensate (acidic water) to an external drain. Sometimes, in cold weather, a condensate pipe can freeze, causing noise in the pipes. Your boiler should have a fault code notifying you when its condensate pipe is frozen.

What you can do

There are tutorials online that show you how to thaw a condensate pipe safely. If you're not fully confident doing this yourself, you should call a registered engineer to thaw your condensate pipe.

10. Boiler keeps switching off

This can be caused by various issues – for example, a thermostat problem, low water pressure or lack of flow.

What you can do

Check pressure and thermostat as suggested above in issues five and eight. If adjusting the thermostat, bleeding the radiators and/or re-pressurising the system fails, call a registered boiler engineer to repair your boiler.

Are you having boiler problems?

The best way to deal with boiler problems is to be proactive. You can save money and avoid stress in the long run by protecting your heating system or boiler with our maintenance and service plan. These include a yearly service.  We’ve also teamed up with BOXT, who have over 16,000 5-star reviews on Trustpilot(1), to replace your boiler.

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