Hi, I have a Vaillant ecoTEC Plus 831 combi boiler, when the hot tap is turned on the water temp keeps going between very hot and cold sometimes it works OK, I can see the temp display dropping and then rising again also can hear the boiler cutting out then cutting in again. I once heard a clunking noise from the boiler while trying to run hot water but this has only happened once. Had someone come and have a look at it but while he was here it worked fine. Has anyone got any idea what might be causing this. Thanks for any advise.
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Vaillant combi boiler problem
- Thread starter DaveOC
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Did you ever get to the bottom of this, Dave? I’m having the exact same issue with the same boiler. Appreciate it was a while ago now.
When ours did something similar it was the flow sensor. Not sure on that exact model but on on ours it's a little impeller that spins when the water flows and that triggers the heat. Except it was gummed up with limescale and spun erratically. A quick clean and all was good.
Phex.
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Coupled with canoe filter or just the latter.
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