uh8 heatmiser

[christhebestia]

Hi All

Help required if you can, so I have a multi zoned UFH system (6 zones ) on an S Plan. The basement UH8 works perfectly with all Therms down on temp power light only on, if temp pushed up then that relevant zone comes on and the pump and valve light comes on as should and when shut down goes back into standby mode with the power light on only. So heres the problem zone for the first floor when heating is called for the pump valve and zone illuminate as should but when switch off the zone light fades out extremely slow but does eventually go out but the pump and valve continue to run. This is happening on two of the six UH8's and they are brand new.

 

[CBW]

They might be new, but sound faulty.

 

[SimonH2]

There are many ways to get the wiring wrong, and without knowing exactly how it's wired, it's impossible for any of us to say if that's the problem. They are really simple devices, so I can't see how one could be faulty in the way described.
As you say there's six, and brand new - my assumption is that this is a new install. If so, no guarantee that the wiring is all correct.

 

[christhebestia]

the fault lies between the uh8 and stat, the stat is low volt and sends a signal to a relay that then sends a signal to the UH8. Ive taken out all the therms on one UH8 and attached a cheap rotary therm and it works perfectly. I have now sent of to wandsworth for new thermo relay. TY for your help tho

 

[DetlefSchmitz]

Last time I had a similar issue I found a relay had a dry joint. But there's any number of possibilities, so drawing out the circuit and then fault finding with a meter is really the only way.