A Checklist of Common Boiler Faults

Below are some scenarios that you may encounter if your boiler begins to fail. They are by no means comprehensive, but they are some of the more common problems encountered. Please note, however, that boiler maintenance can be dangerous and that ideally you should not touch your boiler unless the fix is small such as re-lighting a pilot light.

1. If you hear a hissing or banging type of noise from your boiler or pipes, it maybe due to one of or a combination of these factors which is normally a culmination of the system overheating –

There could be a build up of limescale, which is caused by hard water. This could be treated by shutting down the boiler and pump, treating the system with descaler, draining, flushing and restarting the system.

There maybe a problem with the boiler thermostat. To troubleshoot this you should shut down the boiler whilst leaving the pump working in order to pump water around the system to cool it speedily. When the boiler is sufficiently cool, try to operate the boiler thermostat control. If it doesn’t click, there could well be a problem and you would need to call an engineer to look into the problem.

If you are using a solid fuel boiler, the chimney may have become blocked. This can be swept clean.

There maybe a lack of water in the system. To check this you should shut down the boiler first, then check the feed and expansion tank in the loft. If this is empty, the valve could be stuck. Alternatively, you should check that the mains water supply has not been accidentally turned off or if the pipes have become frozen (in icy conditions).

2. If the boiler is simply not working you may wish to check the following

The gas boiler pilot light has gone out. If it has, it can be relit by following the respective boiler instructions. If the pilot light will will not remain lit there may be a problem with the thermocouple – a device designed to shut of the gas supply in the event of pilot light failure. If the thermocouple is faulty of it detects a fall in temperature is will disable the flow of gas so as to avoid a potentially explosive build up of gas inside the boiler.

The boiler thermostat maybe too low, which gives the impression that, the boiler is not working. This can be easily checked and switched higher if required.

The boiler timer or programmer may have ceased to work or is set incorrectly. This can be tested and reset. If problems persist, the timer may need to be replaced by a qualified engineer.

The boiler may have insufficient water pressure – combi boilers will generally have a ‘filling loop’ which allows the injection of additional water under mains pressure from your domestic mains water supply. If the pressure falls below a preset level your boiler may not function. Pressure levels should be checked regularly and your boiler manual will give you additional information on recommended pressure levels and the frequency with which they should be checked.

It is imperative to be aware that boiler maintenance is an extremely specialised and dangerous area so even if you are confident that you can diagnose a problem with your boiler it is always advisable to consult with a CORGI registered engineer and have them do the work for you.