Boiler heating but not circulating water into UFH

[CoachRich]

Hi, I wonder if anyone would be able to help me with an UFH question.
I have an UFH with 4 zones controlled by NEST thermostats and a Vaillant boiler.
The UFH has stopped working totally.
When I turn the thermostats up, the boiler fires up but does not seem to produce hot water (it just shows the egg timer and the pipe coming to the UFH is cold). When the demand comes from upstairs (radiators) the boiler works fine i.e. the hot water is flowing OK in the radiators without the egg timer..

From what I see the lights are off on both UFH pumps (no power to both pumps) but the heatmiser and nest lights are OK.
I wonder why the hot water is not flowing out of the boiler to the UFH, is it a problem on the boiler side, or the UFH pumps not receiving a signal or something else?

Many Thanks

 

[Stuckinarut]

It might be the pump has failed or the actuators for the ufh - unusual that all 4 would go. Is there a motorised valve anywhere controlling this?

 

[CoachRich]

Thanks for the reply. Yes there are actually two pumps so I don't think they would fail at the same time. There is no live power to the pumps when I test but I am not sure if the power only comes on when needed if that makes sense or they are always powered?
There is a motorised valve (on the photo with live power and that seems to be fine (i have tried to put it in manual mode).

The pipe under the boiler feeding the UFH is cold, no water circulating despite the nest triggering demand

 

[Stuckinarut]

Unfortunately volt sticks aren’t that reliable and only generally used as a safe to touch instrument. I would say the motorised valve isn’t fully actuating, doesn’t explain why the boiler isn’t firing tough, although could be something else. Putting the motorised valve into manual only means latching it open, not to trigger the boiler/pump.

 

[Madrab]

+1 you need to get a voltmeter out and confirm the circuit.

You need to understand where the UFH's pump and 2 port gets its power from. If it's the UH4 control centre powering them then usually the 2 port and the UFH pump's supply is managed directly by that on the same output connection, so you want to check that the control centre is outputting 240v to the 2 port and that it is actually opening and then check the pump is also receiving the same 240V.

If there is power getting to them both but the manifold pump isn't running, then chances are the pump's failed. Where is the other pump, just as normal connected on the CH system? Or is it a system boiler with an internal pump?