Boiler fault: 7 common causes and what you can do yourself

A boiler that breaks down almost always does so at the worst moment: on a cold morning or just as you want to shower. Often the cause is small and you can check something yourself first. Below are the seven most common causes, what you can do and when to call an engineer.

1. Water pressure too low

The most common cause. Below 1 bar the boiler shuts down for safety. Check the pressure gauge; if it is too low you can top up via the filling tap to about 1.5 bar. If you have to top up often, water is leaking somewhere and it needs investigating.

2. Ignition problems

Does the boiler try to ignite but fail to light? The ignition pin or the gas supply may be the problem. Check that the gas tap is open. If it continues, an expert check is needed.

3. A dirty or limescaled heat exchanger

Limescale and dirt reduce heat transfer and can cause overheating and faults. You prevent this with regular boiler maintenance.

4. A faulty pump or stuck three-way valve

Is your water warm but the radiators are not (or vice versa)? The circulation pump or three-way valve may be stuck. This is a job for an engineer.

5. Air in the system

Air in the radiators causes poor heat distribution and can make the boiler intervene. Bleed your radiators and then check the water pressure.

6. An error code on the display

Modern boilers show an error code that points directly to the cause. Note the code and pass it on when you report the fault, so we arrive well prepared.

7. No hot water, but heating works (or vice versa)

This often points to a problem with the hot-water function or a sensor. Call us and we will trace the cause and in most cases fix it on the spot.

What can you safely do yourself?

• Check the water pressure (1 to 2 bar) and top up if needed.
• Try a reset according to your boiler manual.
• Check that the gas tap and the plug are in order.
• Bleed the radiators if heat distribution is poor.

Not working, or the fault keeps coming back? Call us straight away on 020 244 2926 or book an appointment online. See also our page on breakdowns and the rates for a breakdown visit.