DIY Doctor

Underfloor heating stopped calling for heat

Postby A1cap0ne » Tue Nov 17, 2020 5:25 pm

I’ve had wet ufh working fine on timers in my extension for nearly 2 yrs then last week it stopped working.

It is a single zone, with manifold, heatmiser digital thermostat, and 2 port zone mechanical valve connected to a comi boiler setup.

The CH side is working fine, it has a nest thermostat and a 2 port zone mech valve.

Now when the ufh comes on, the pump works but there is no independent call for heat to the boiler and the mech value does not switch on. Like I said this was working fine until last week. No changes have been made.

I can turn the mech value manually and the ufh will work when the CH is on. If CH is not on it just pumps around normal water.

what could the issue be? From what I’ve read up on, if it was just the valve not working I assume it would be the motor at fault? But why is is now not calling for heat from the boiler? I’d appreciate any help before I call anyone out. TIA
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Postby ericmark » Sun Dec 06, 2020 12:43 pm

Sorry for late reply, UFH uses many methods, and hard to know which yours uses, however the micro switches in motorised valves do fail, and so most likely is the motorised valve head or motor, theory you can change micro switches, but in practice normal to change whole head.
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Postby B4Less » Thu Dec 10, 2020 9:52 am

If the valve is not turning on then it is very likely that it is also then not calling for heat. The transition from closed to open is what then calls the boiler to come on due to a relay on the motorised valve or fuse board. I would suggest replacing your motorised valve and everything should be back up and running also.
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