Common Boiler Faults
|No heat or hot water||There are multiple cures for this, which include broken diaphragms and airlocks, failure of motorised valves, issues with the thermostat or low water levels. |
A good place to start is to check if your boiler is not working because of an issue with boiler pressure or your thermostat. You can find more information on these issues and how to fix them below.
If you think you may have a broken diaphragm, airlock or valve it may need to be replaced with a new part. We recommend calling out a Gas Safe registered engineer who will be able to thoroughly diagnose the problem and replace any broken parts where necessary.
|Leaking and dripping||A variety of issues could cause your boiler to leak water. It will depend on where the water is leaking from to determine the cause - however you should never try to fix a leaking gas boiler yourself, always call out a Gas Safe registered engineer.|
The most common cause is a broken internal component, such as a pump seal or pressure valve. If the leak is coming from the pressure valve it may be a case that your boiler pressure is too high. If it's coming from the pump seal, it may have become worn out and need replacing.
You may also find your boiler is leaking around the pipes or tank - this can be a result of corrosion or in some cases where the system has not been fitted properly. In any case, we recommend calling out an engineer who will be able to diagnose and fix the issue for you (in in the worst case advise if you need to replace your boiler).
|Strange banging, whistling or gurgling noises||Air in the system is a common cause, alternatively it could be that the water pressure is too low or it's kettling. Imminent pump failure, particularly in older systems, could also be responsible for strange banging noises.|
You might be able to determine the type of problem your boiler is having based on the type of noise it is making. For example a noise similar to that of a boiling kettle is usually a result of kettling (you can read more about this below). Our guide to central heating noises can help you determine the cause of your noisy boiler.
|Pilot light goes out||Could be a broken thermocouple which is stopping the gas supply, a draught blowing the pilot light out or a deposit built up in the pilot light. |
It is worth checking that there are no issues with your gas supply before trying to reignite a pilot light - for example if your gas stopcock is on but your boiler is receiving no gas, or if none of your other gas appliances are working you should contact your gas supplier. You can then try relighting the pilot light yourself - ensuring you follow the instructions found in your boilers manual for igniting the pilot light.
If neither of these things work you should call out a Gas Safe registered engineer. Always remember that you should never carry out and work on your own gas boiler.
|Losing pressure||if your boiler pressure drops too low, your central heating system may not function properly. |
To check a boilers pressure level, simply look at it's built in pressure gauge - if it's below 1 you may have an issue. There a number of reasons why this may be happening: a water leak in the system, the pressure relief valve needs replacing or as a result of recently bleeding radiators.
The first thing to do is check for a visible leak in the system. If you find one you should call a registered engineer, if not you could try repressurising the system. Only do this if you feel comfortable doing so (if not call out an engineer) and ensure you follow your heating systems manual. Visit our guide to low boiler pressure to learn more.
|Frozen condensate pipe||Condensing boilers have condensate a pipe which transports the acidic water, caused by waste gas, away from the boiler. This usually runs outside into a drain, and because of its location it faces the risk of freezing.|
A condensate pipe can be identified simply by looking at your boiler. Underneath the boiler you will see pipes entering and exiting - if you have a plastic pipe (usually white and roughly 2cm wide) and the rest are metal then this is likely the condensate pipe. It should lead outside of your property, into a drain.
Your boiler will often have a fault code or warning notification if your condensate pipe has become frozen. Whilst there are tutorials online to thaw a frozen condensate pipe by pouring warm water over it, if you feel unqualified or unsafe doing so you should call out a registered engineer.
|Thermostat issues||If the thermostat is losing accuracy or turning the heating on/off when it's not supposed to it might be time to invest in a new one. |
It's worth making a couple of common sense checks first though, as sometimes these can be easily overlooked.
- Check your thermostat to ensure it's in the on position and that it is set to the correct settings i.e time and schedule - it's always possible that it could have been knocked.
One other consideration to make is that your home might be warmer than you think and a thermostat won't allow the boiler to heat your home higher than the temperature it has been set at. If this is the case then try increasing it in very small increments until you find the temperature that's right for you.
If none of the above apply it's possible that your thermostat may have malfunctioned or lost accuracy over time, in which case it is probably time to consider a replacement.
|Kettling||Hearing a strange rumbling noise similar to when a kettle is boiling? This can happen when lime scale or sludge builds up on your boiler's heat exchanger. When these deposits build up in your boiler, they can restrict the flow of water within the heat exchanger. This can overheat the water, causing it to steam and boil (causing the kettle-like sounds).|
Kettling is more common in areas with hard water, but can also affect boilers in soft water areas. Not only does it cause your boiler to work harder and thus cost more to run, it can also shorten the system's life. If your boiler is kettling, it's advisable to call out a gas safe registered engineer who will likely flush out your system to remove the build-up of these deposits and ensure the system is working efficiently once more.
|Radiators not getting hot||You might find that not all of your radiators are getting hot or that only the bottom section is heating up. This can be down to a number of reasons but the two most common are sludge or air build up in the system and unequal distribution of heat.|
If only the bottom of your radiator is getting hot, you may need to bleed it. This is fairly straightforward and doesn't require an engineer (unless you don't feel able to carry out the task yourself).
If you find certain radiators in your home are not getting hot, your radiators could need balancing. This can also be done without the help of an engineer if you feel confident in doing it. The process involves adjusting the valves on all of the radiators in your property, to ensure each is getting enough hot water to work effectively.
If the above did not work you may have an issue with sludge build up preventing a free flow of hot water to the radiators. Chemically cleaning or flushing the system should remove these deposits - we would always recommend hiring a qualified engineer to carry out this job.
|Boiler keeps switching itself off||Could be low water pressure, a problem with the thermostat or a lack of water flow due to a closed valve, air or the pump not circulating the water in the system properly. We've covered each of these issues in more detail above, but if you still can't identify the cause we recommend calling out a Gas Safe registered engineer to take a look at your boiler.|
(Boiler Guide. 2019. Top 10 Most Common Boiler Problems. [ONLINE] Available at: https://www.boilerguide.co.uk/articles/boiler-problems/top-10-most-common-boiler-problems. [Accessed 2 August 2019].)