Vaillant boiler not heating

8 Sep 2012
Reaction score
West Midlands
United Kingdom

I have a Vaillant system boiler (627) it doesn’t heat the house up. I’ve even tried turning hot water on. It’s connected to a vsmart.

chimney sweep seems to work.
it has a egg timer tap and rad symbol.

Any idea?


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Are all radiator valves fully open? Any work carried out recently? Is the temperature on the front of boiler high enough?
Felt the heating flow pipe. Not warm. Radiators occasionally get a very slight heat. But then stop. No work carried out. Valves fine. The hall way rad don’t have a trv and that’s not warm. I’ve tried turning off water incase of hot water priority. Still no luck. Chimney sweet works ok. This is what it’s like without water on. I notice very slight heat on rad. Nothing more. I’m using a vsmart. It’s a eco boiler that’s been condensing a LOT. Maybe that’s worn it out?


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Of the 4 rectangular buttons, Press the right hand top button, twice (once to wake it up), have a look at the temperature. I doubt it’s worn out.
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Boiler says 39. Target flow tempreture is 75(but that’s override by vsmart temp control anyway. I’ve set vsmart to 30 degrees to be sure.
There’s something stopping it getting to temperature. A filter valve closed perhaps?
I’d have probably guessed this , as your display (usually the flow temp) is showing 29 on first photo and 32 on second. Chimney sweep is max rate and not for very long. Could be your vsmart playing up then, I don’t have experience on these, perhaps one of the Vaillant pro’s can help.
It isn’t warming up properly now. So it’s a fault between boiler and vsmart. Well I’m gonna call vaillant tommorow

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