How to identify and fix basic boiler problems

Boiler problems can be difficult to diagnose but there are some faults that are common across all types of boiler. Fixing some faults on the boiler yourself is quite possible but you should never attempt to do any GAS work on the boiler yourself, this should be left to a qualified engineer that is gas safe registered. Below we have put together some of the faults which are common across all brands of boilers, if you cannot find the solution to your specific problem please ask in the central heating forum. You may also find the central heating problems page useful as boiler problems and central heating problems are often closely related.

Often boiler problems will become apparent during cold weather which can often add to the urgency of getting the boiler fixed quickly. For many boiler problems you may need an heating engineer but below are some of the easy to fix problems that any competent DIY 'er should be able to fix.

  • Boiler Pressure! Some sealed systems will require a certain pressure in the system for it to operate, if the pressure is too low or too high the boiler will not operate. This can often catch people out, the pressure can drop in a system if there is a miniscule leak in the system of it the central heating radiators have recently been bled. Pressure can be too high in the system if the filling loop has been left connected and the valve is passing slightly, for this reason it is recommended to always disconnect the filling loop after the system has been pressurised. To check the boiler pressure and re-pressurise the system please see here- how to re-pressurise a boiler


  • If the boiler pressure has dropped and you re-pressurise the system and the next day the pressure has dropped again, this can be a sign of a faulty expansion vessel. If the vessel is faulty and the heating is say at 1 bar and the boiler heats the water in the system the pressure will increase, the expansion vessel allows the water to expand under normal conditions and so the water will stay at a pressure of perhaps 1.5 bar when the central heating is on. If the expansion vessel is not working the pressure goes too high, which causes the pressure relief valve on the boiler to open. When the central heating cools down and the water contracts the pressure will of dropped significantly in the boiler and the boiler will not operate at this pressure. This fault can become more apparent after bleeding the radiators because a radiator containing a lot of air can act as an expansion vessel. There is more on the subject here- Expansion vessel | Checking an expansion vessel | recharging an expansion vessel | Fitting an external expansion vessel


  • Blown fuse! This may seem obvious to many people but this again can catch people out. Check that the boiler has electrical power going to it, most boilers have some illuminated display of some kind, if there is nothing lighting up then check the electrical supply to the boiler. How to check for a blown fuse can be found here Blown fuse testing


  • No fuel! Another obvious point that is often overlooked is to check that the boiler is getting Gas, this is often a problem with pre-payment meters as they can often run out of gas. If the boiler has no gas it will not work! Often a good place to check if you have Gas is by testing out the cooker or hob.