How to diagnose common boiler problems

Your hot water and central heating are entirely reliant on your boiler, making it the nerve centre of your home.

It's important to check that your boiler is fully functional to keep you and your home warm throughout winter. Follow our handy hints to help you identify common boiler problems:

Electric supply

Is your electric supply switched on? If not, you’ll need to contact your electricity supplier.

Gas supply

  • Check the emergency control valve, is it open? If not, open the emergency control valve to allow gas to flow through.

  • Is the boiler gas supply on? If your gas stopcock is open but no gas is flowing through then you have a problem with your gas supply. In this instance you’ll need to contact your gas supplier.

  • If you have an oil boiler check there’s enough oil in the tank by reading the gauge.

Pilot light

  • Is your pilot light igniting? In some cases you can relight the pilot light by following the manufacturer’s instructions. These are often printed on a boilers door, near the pilot light, on the front panel of a boiler or in your boiler instruction booklet.

  • If your boiler doesn't have a pilot light, press the de-blocking button. If that doesn't work, check the central heating pressure is set to the manufacturer’s instructions; most commonly it’s set to one bar. If that doesn't work and the central heating pressure is correct, you either have a gas supply problem in which case you’ll need to contact your gas supplier. If your gas supplier can’t help then you’ll need to call in a Gas Safe Registered professional for a repair.

Boiler controls and thermostats

  • Is your central heating thermostat in the on position? Try increasing the level of your boiler or central heating thermostat. Worth noting that the boiler will only work when the thermostat is set higher than the room temperature.

  • Check the age of your thermostat. Over time thermostats can lose their accuracy resulting in your thermostat misreading temperature settings and turning the heat on/off at incorrect times. A Gas Safe Register professional can clean and recalibrate your old thermostat, but it’s worth noting most newer models of thermostats include good energy-saving controls. 

  • Is the timer on your central heating controls working and is it correctly set? Does it switch on? If not you may have flat batteries or a problem with the power source.

Electronic programmers

Check that the LCD display, circuit board electronics or relay haven’t failed. If you need to replace the programmer, make sure the new one has a universal backplateThis makes future replacements simple, allowing you to plug in a new programmer without having to call in a professional.

Condensate pipe

Is all in order with your condensate pipe? During extremely cold weather the condensation in this pipe may freeze and cause a blockage causing the condensate to ‘back up’ into the boiler and cause a shut down.

Signs that the condensate pipe may have frozen include your boiler’s display showing a fault code or warning lights as gurgling or bubbling sounds come out from your boiler or condensate pipe. If you suspect this is the problem, you will need to defrost the condensate pipe.

Adjusting a radiator valve

There are two types of radiator valves; a Thermostatic radiator valve and a Lockshield valve.

  • If you have a thermostatic radiator valve on your radiator you can adjust it to the heat you need.

  • If you have a conventional Lockshield valve, remove the plastic cover and adjust the setting using the right tool (these can be found at most DIY stores).

If there’s no change in temperature after you’ve adjusted the settings you have a fault with your radiator valve and will need to call a Gas Safe Register professional to drain the system and replace it.

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