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Boiler Common Faults

Here are a few common faults associated with boilers.

            Pilot Light Will Not Light


  • Ignition fault - check the ignition lead this could be damaged causing it to spark in the wrong place. Check the spark electrode (the white porcelain part near where the pilot lights) again this could be damaged causing it to spark elsewhere. And finally check the spark generator (the thing you push in/click to get a spark) for the same fault as the others. Seal the damaged component if its sparking in the wrong place this will force it to the right location. If irreparable just replace faulty part.


  • Pilot will not stay lit - probably the thermocouple (t/c lead for short). You can check this by buying or borrowing a t/c lead checker. These can be usually identified as faulty because the end will have a burnt hole in it. Not able to repair just replace.


  • Dirt in pilot - caused if not serviced regularly or if the appliance is in a dusty room. Clear out the pilot to remedy this problem.


  • Blocked pilot light supply - checked by undoing the pilot tube and blowing down it. Clear out any blockage found.


  • Gas valve/solenoid - check there is power to the solenoid (some models), if there is and its not doing its job then replace it. If you undo the pilot tube from the gas valve then press the plunger to allow gas and there is not gas then the gas valve is at fault. Replace or remove blockage.

            Noisey Boiler


  • Boiler "kettle-ing" - kettle-ing is a term used by heating engineers to describe this sound (similar to the sound a kettle makes when its boiling). This is caused by the boiler over heating due to a faulty boiler stat. You may notice the radiators feel hotter to touch. A faulty boiler stat can cause the system to overflow (due to expanding water being dumped back into the f/e heating tank) and drag in air. This combined with the fresh water (from the heating tank filling back up once cool)will cause sludge in your system. And as the boiler stat is a major safety control should be replaced immediatley


  • Loud banging noise - this is usually caused by the pump not working, be it sezied or just come to the end of its working life. So either free the pump or replace it. Also check any bypasses fitted are open. This is a loud noise and sounds like there is someone thumping the boiler, it can alarm some people as they think the boiler is going to blow off the wall.

            Main Burner Not Coming On


  • Boiler thermostat turned down - simple turn it back up. This could have been turned down either on purpose or by accident by someone and you've not known or forgot. Or may be its been turned down for summer and needs turning back up for the colder periods.(The boiler thermostat is found at the boiler and will usually be a dial.) Check to see if their is power to the boiler stat, if there is and its not doing its job then replace. If there isn't power then the problem is further up the line.


  • Check the programmer - check to see if there is a call for heat or hot water i.e you have pressed heating or hot water to constant or if your using a timer it should be in the on period.


  • Check the roomthermostat - again this may be turned down or it has reached temperature. Try turning it up. This can be checked electrically if it doing its job then ok - if not replace.


  • Gas valve - if there is power to the gas valve but its not lighting then the gas valve must be replaced. (Or you may be able to just replace the solenoid on some models.)

Related Topics

If you haven't found what you are looking here maybe the boiler manual section would help you. On that page are links to all available boiler manuals. Or if it was something else you were after contact us  and we may publish the information you need.

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