Glow-worm Boiler Not Firing Up

Glow-worm Boiler Not Firing Up? Troubleshooting Advice

Last updated on February 22nd, 2024

Everyone will experience their boiler not firing up at some point, which will probably ruin your day, especially on a cold winter’s night. Your central heating system not getting hot is a nightmare.

I have been fixing boilers full-time for over a decade and have come across many Glow-worm boiler problems when I get called to a boiler that’s not firing up.

Common Reasons for a Boiler Not Firing Up

There are some very easy fixes for a boiler not working.

Glow-worm boiler in cupboard

Here are some things you can troubleshoot and check yourself:

  • No power supply
  • No gas supply
  • Low boiler pressure
  • Thermostat problems
  • Frozen boiler condensate pipe

No Power Supply

When your boiler is not working and you have no lights on the boiler, there is a good chance you don’t have any electricity to the boiler.

Fused switched spur and fuse
Fused switched spur

Here are some things to check:

  1. The fuse in the switched spur next to the boiler (should be 3 amp)
  2. The circuit hasn’t tripped at the consumer unit (main fuse board for the house)
  3. The fuse in the boiler (usually 2 amp)
  4. You have money on a pre-payment electric meter

No Gas Supply

Having your boiler go to lockout when it tries to fire up could mean you don’t have any gas getting to the boiler.

Gas meter turned off
Gas meter turned off

Here are some possibilities:

  • Gas is turned off at the gas meter control valve
  • Gas credit has run out on a pre-payment gas meter

Low Boiler Pressure

Low boiler pressure is a very common reason for a boiler not firing up. You will need to repressurise the boiler to fix this problem.

Baxi boiler pressure too low
Low boiler pressure

Having low boiler pressure is an easy fix but if your boiler pressure keeps dropping, that means you have a problem that needs to be found and fixed.

Thermostat Problems

Hive room thermostat being set
Room thermostat

A thermostat problem could be the reason your boiler is not working.

Here are some things you can check:

  1. The thermostat temperature is turned up
  2. The batteries are good (on wireless thermostats)
  3. Faulty thermostat

Frozen Boiler Condensate Pipe

A frozen boiler condensate pipe will probably be the reason for your boiler not firing up if it’s below freezing outside.

When a boiler condensate pipe freezes, the boiler will go to lockout until the pipe has been thawed out.

frozen condensate pipe
Frozen condensate pipe

Which Parts Cause a Boiler to Stop Working?

Heating But No Hot Water

Having no hot water from the boiler but the heating is working could be caused by many things.

Combi Boiler

A combi boiler not firing up for hot water could be for one of these reasons:

  • The plate heat exchanger is blocked
  • The diverter valve is stuck or damaged
  • The temperature sensor is broken
  • The flow/micro switch is broken
Worcester plate heat exchanger
Plate heat exchanger

Heat Only or System Boiler

  • A 2 or 3-port valve is stuck or broken
  • The hot water cylinder thermostat is turned down or faulty
  • The programmer is not working properly

Hot Water But No Heating

When the central heating is not working but the hot water is, there could be many different reasons for this.

Here are some of those reasons:

Combi Boiler

  • The diverter valve is stuck or damaged
  • The room thermostat is turned down, broken, or needs the batteries replaced
  • The temperature sensor is faulty

Heat Only or System Boiler

  • 2 or 3-port valve is stuck or broken
  • The room thermostat is turned down, broken, or needs the batteries replaced
  • The programmer is not working properly

Pilot Light on Boiler Not Firing Up

A boiler pilot light is a constant small flame that is used to light the burner when the heating or hot water is called for.

Modern boilers don’t use pilot lights anymore, they use spark electrodes which fire the boiler up using electric sparks every time it’s needed.

If you have an old boiler with a pilot light and it’s not firing up, here are some potential reasons:

  1. Gas supply problem (blockage or no gas for example)
  2. Gas valve problem

If the pilot light is on but not firing up the boiler, this will usually indicate a faulty gas valve problem.

Boiler Clicking But Not Igniting

A boiler clicking but not igniting means you are getting electricity, and your external controls are working, so it has to be something further on in the firing-up process that’s causing the problem.

Here are some potential reasons why it’s clicking but not igniting:

  1. A gas supply problem
  2. The spark electrode is faulty
How to read a gas meter

Glow-worm Faults

Here are some more guides for other Glow-worm problems:


When your Glow-worm boiler is not working there are a few simple things you can check yourself without having to open the boiler up.

If you have a central heating radiator that’s not working then this will be a radiator problem, not on the boiler.

When it comes to needing boiler parts to be fixed or replaced you should call a gas engineer to get it checked out properly and fixed.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

    View all posts
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1 thought on “Glow-worm Boiler Not Firing Up? Troubleshooting Advice”

  1. Hi, I have a Glowworm Ultrapower 170 SXI and the boiler stopped working and turned itself off. I have restarted the boiler at the fused spur and F9 started flashing showing the pressure at 4.5 bar(!) When I opened the cover, I noticed that there was a fair bit of water everywhere probably from the expansion vessel that was changed few months ago together with the prv. I dried all off and reset the boiler with the push button on the panel. Boiler fired up and worked for 10 minutes and went back to F9. I drained off the rads a fair bit hoping the pressure will reduce but that did not help.
    Now the boiler will not start and I have no idea if the pressure reading is true or false. Any thoughts? Any suggestions will be happily received as trying to get the boiler working before end of day so kids can have a shower before tomorrow’s gcse exams start.
    Many thanks

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