Boiler not working? Find out why and how to fix it

A boiler should give you 15–20 years’ service, so if it’s relatively new and you’ve kept up with your annual service routine, it can be baffling and irritating if it suddenly stops working. Your first instinct will probably be to call out a Gas Safe engineer, and if you don’t feel at all confident eliminating the checks we’re giving you below, please do. Although you’ll probably be charged, it’ll give you peace of mind.

Problems you can check for and possibly fix

These are relatively routine issues that you or a friend or relative might be able to fix.

Power supply

If there’s no power, the boiler won’t work at all. If your lights aren’t working, it could be a number of things: roadworks outside (although you should have been informed), a general power cut or a problem with your home’s power supply. If you have a pre-payment meter, check it’s topped up.

If your power is definitely on, check your consumer unit, better known as a fuse box. If one of the circuit breakers is in a different position to the others, it could have tripped. Flip it back. While this does happen from time to time in the event of a surge or a bulb blowing, it’s probably worth getting an electrician to look for faults.

Water or gas supply

Your boiler’s central heating will still work if the water is switched off, but it will affect your hot water. If you have a combi boiler, you’ll notice straight away. With a system or conventional boiler, you’ll notice when the tank empties. If you have no cold water from the taps, there’s your problem. It might have been turned off for construction works or the pipe could be frozen.

If you have a gas hob, turn it on for a few seconds. If the flame dies down quickly, your gas must be switched off. If you have a pre-payment meter, check it’s topped up. If you suspect there’s no gas, there must be a wider problem, so call your gas supplier. If your boiler is your only gas appliance, it’s a bit more difficult to check, but look at the panel for error messages. Perhaps you could ask a neighbour if their gas supply is working.

Water pressure too low

Check your pressure gauges on your boiler. They could be dial-type or digital. If they are below 1 bar, your boiler will probably trip out automatically. Top up the water using your filling loop. Consult your boiler’s manual for instructions, but it’s fairly easy for anyone to do. If this happens repeatedly, there must be a problem with the system – call a Gas Safe engineer.

Pressure too high

On the other hand, the pressure could be too high. This too will trip the system for safety purposes. It’s unusual for the pressure to rise quickly unless it was accidentally overfilled, so there could be a problem with your pump or expansion vessel. For now, though, you can lower the pressure by bleeding or draining a radiator, depending on how high the pressure is. We’ve written about doing that here.

Frozen condensate pipe

If it’s below zero outside, it’s possible that the condensate pipe has frozen. This is often a small finger-sized pipe (not your main flue) that sticks out of the wall, and usually folds back on itself, but sometimes it’s a long pipe that goes down to a drain. If that freezes, condensate will have nowhere to go, and the boiler will shut down. Gently warm up the pipe with tepid water – do not use boiling water. You can help prevent freezing in future by insulating the pipe.

Sludge in the system

A build-up of sludge could have got so severe that it’s blocking the main pipework, pump or heat exchanger, which will cause the boiler to trip. We’ve written about removing sludge in our article on radiators that are cold at the bottom. 

Radiators turned off

If you’ve got hot water but no central heating, check that your radiators are individually turned on. Some people turn them off over summer, although it’s always best to have at least some water circulating around them.

Thermostat set too low or faulty

Is your thermostat turned down too low? Your heating will never come on if your thermostat’s temperature setting is lower than the temperature in the home. Turn it up to about 20 °C, make sure your timer isn’t overriding the heating, and see if the heating comes on. Failing that, you could have a faulty thermostat.

System crash

Modern boilers have a computer inside them that controls and monitors all the systems. They’re relatively simple systems and are not particularly prone to crashing, but every now and again, they might benefit from a system reset. This is often achieved by poking the end of a pen into a button that’s sunk into the control panel (check your manual), but if you can’t find such a reset button, try switching the boiler off and on again. It will reboot the system and might iron out any bugs.

Problems that need professional assistance

If you’ve investigated all of the above, the problem is probably more than the average homeowner can tackle. You’ll have to get in touch with a Gas Safe registered engineer so they can diagnose and fix the boiler or clean out the system.

You might see error messages appearing in your control panel. Your user guide should tell you what they refer to. If it’s one of the problems listed above, you might be able to fix it, but otherwise note down the message or its meaning, and tell the engineer what it is when you call.

Some of the commonest problems include the ignition not working, a leak in the boiler or heating system, a pump failure, a problem with the internal electrics or an expansion vessel failure. None of these issues can be fixed by an unqualified person, so please don’t attempt to work it out yourself.

Be aware that the problem could well be terminal, and if your boiler is old and out of warranty, that might mean you need a new boiler. Have a look at our tool for selecting a new boiler then book a local fitter that we’ve approved – you can do all that without leaving this website.

Having problems with your heat pump? Take a read of our expert guide to air source heat pumps or speak to our experts for more information.