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Mend Chaffoteaux & Maury Britony Combi Central Heating Lockout

Why does my boiler go g-g-donk and then lock out?

My Chaffoteaux & Maury Britony combi has an intermittent problem. About a minute after turning hot water off, it starts to make a g-g-donk sound, about once a second for about 30 seconds. Next time I turn a hot tap on, it doesn't try to ignite, locks out (red warning LED lights) after 8 seconds, and has to be reset. It then starts normally. The selector switch is set to DHW only, i.e. central heating is turned off. I think the noise comes from the bottom right corner but can't be sure. Does anyone know what could be wrong?

Tony
August 2008

Chaffoteaux & Maury Chaffoteaux & Maury Britony Heating, Home Heating Systems Combi Central Heating Lockout

This answer is from the guy who put the question in the first place. My boiler is now working perfectly.

I found 2 problems. First I suspected there might be air in the system, so I replaced the air separator. The old one was well and truly gunged up, so it might not have been working properly, but it didn't fix the symptom.

Second I bought some descaler from my local boiler repair place and descaled the secondary heat exchanger. Loads of black stuff came out of it. Bingo - problem fixed!

Tony
February 2009