Portrait photo of Mike Bryant, AKA Mike the Boilerman

Mike the Boilerman -

Your Gas Safe Registered boiler 

and central heating repair technician in west Berkshire. Willing to travel :)



I am still carrying out house visits. Full details explained


(Last updated 21st April 2021)

Glow Worm HXi

12HXi, 15HXi, 18HXi, 24HXi, 30HXi

‍ If your HXi needs repairing call me on 07866 766364.

The HXi is a broadly reliable modern high efficiency condensing boiler but like many modern condensing boilers, is terribly prone to control board failure. The user display goes blank particularly if the power is turned OFF to the boiler for any reason, so unless you have to, don’t turn the power off!

Things to check if your HXi isn’t working:

1) The central heating programmer is set to ON and the room thermostat set to a ‘high’ setting.

2) The temperature control on the boiler is at a high setting not zero. 

3) Finally, this item is is only for the more technically competent. There is an overheat re-set button inside the boiler that may need re-setting. It is behind the inner front cover and not designed for the user to access. Strictly speaking only a competent gas technician should remove the outer combustion chamber cover, but users have been known to look in the manual to find this re-set button and re-set it themselves….

Other that the above, there is little or nothing the user can do to fix their own failed HXi, but provided the points above have been checked you can be sure a boiler technician is genuinely needed and he or she won’t arrive and do something trivial then charge a massive call-out fee. Call me if you are within travelling distance of me in west Berkshire. 07866 766364.

Common faults with the HXi:

1) By far the most common problem with the HXi is circuit board failure. This boiler is famous for it. Most commonly happens when the power is isolated for a repair of servicing, then on restoration of the mains electricity, the display on the front fails to wake up and the boiler won’t run. A new PCB fixes the problem.

2) Overheating. The overheat protection thermostat on the flow pipe inside the boiler trips and needs manually re-setting. ‘Nuisance tripping’ can occasionally happen but usually this indicates reduced water flow through the boiler, leading to excessive temperature rise in the heat exchanger. There can be a variety of causes. Easiest to fix is when the installer fitted thermostatic radiator valves to EVERY radiator with no bypass circuit - a common error. The valves all gradually close down as the house gets warmer leading to reduced flow through the boiler and the overheat thermostat trips. Keep one radiator valve fully open to fix this problem. The other reasons are usually corrosion deposits contaminating/partially blocking the heat exchanger or pump failure.

3) Fan failure. The boiler simply fails to start, sometimes showing a F-series error code on the user display. 

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Copyright Michael Bryant 2021

Site first published 16th January 2004

Last updated 26th April 2021

Gas Safe Register 197499, CIPHE registration number 56207

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