Underfloor heating issue - Hot Water Light off, system not heating

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(It had to happen when it's cold outside....)

So I've had an UFH heating for 7 years, all been fine. But last night, I noticed that the rooms were chilly and no heat coming through the floor. The thermostats were on, the signals (from all 4 zones) were being sent to the wiring centre ok. I had hot water coming through the taps.

Checked the boiler, and the pressure was very low, so I re-pressurised. Pressure is still fine this morning.

I checked the UFH wiring centre, and the lights are on, but noticed that one light does NOT come on - the one for Hot Water (HW in the photo below).

1) Could it be an electrical/wiring issue with the wiring centre?
2) Could it be a pump issue?
3) With the boiler having lost pressure, I don't know whether that would cause a lack of water/pressure in the UFH system, and so I would need to refill it?

Any help or suggestions would be much appreciated! I tried calling the Heatmiser helpline, but after 10 minutes on hold i was still #14 in the queue.....
 

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Is the underfloor pump running ,is the underfloor zone valve opening
There's a grundfos pump - should there be a noticeable sound coming from it? When I turn on a zone (and I hear the "click" and the light come on in the wiring centre), I can't seem to hear anything at all from the pump. The flow meters are pretty dirty/cloudy as well which probably isn't a good sign either
 
In the pics only one UFH Zone is calling Z1, two UFH thermo-actuators are lit (energised 2 &3 from left), NONE of the flow meters appear to show any flow ... (it does take some time, a few minutes, for actuators to open and allow flow, though).

That suggests no UFH pump working which could/should be fed from the UH4 output? Multimeter may confirm power to the pump? With power off check the pump impeller spins freely by removing the silver air bleed cap and a screwdriver (flat blade)? When powered they get warm to touch on the motor part of the casing (not water pipes) and can get quite hot, especially if 'stalled' for a long time. One can usually hear a little noise and they vibrate a touch - so feel it.

Boiler o/p probably operated the UFH motorised valve to operate the boiler via an UFH zone valve... The motors and/or the end microswitches can fail. Manual opening lever will be 'floppy' if motor opens the valve.

HW controller on the UH4 may not be used? If there is a separate timer for HW (and maybe rads) to control their respective motorised zone valves? Even if used there will be a time-clock input to the UH4 to make the HW relay and lamp work, so that timer needs to be calling for HW.

Water in some flow meters is very mucky, but not all, which seems odd; but likely a summer job unless a big drain down and refill is needed sooner.
 
you guys are all VERY good! Thank you! It was indeed the motorised valve - the little lever is sticking and won't activate automatically, which is why there was no activity from the pump/HW light. If I manually push the lever, everything kicks in and is working as normal. Looks to be a standard Danfoss part for about £40, and I'm assuming a straight plug and play replacement with no need to drain the system or anything drastic like that?

Re the flow meters, I'll follow your advice and leave until it's warmer to do a full drain and refill, maybe replacing the flow meters in the process just so I know everything is clean and tip-top.
 
So the plot thickens. I have 4 zones (with 6 flow meters - for 2 of the zones, there are 2 flow meters associated with them because they each cover 2 rooms).

I turned the 4 zones on via their thermostats, one-by-one. 3 (or maybe even 4, too dirty to see) of the flow meters do not move when the thermostats are turned on, and the floors remain cold. So something not working. I wanted to try and take them off to clean to see if it made a difference, and have followed some youtube videos, but just wanted to be sure of the process and the parts of my manifold (which looks a little different to the ones online).

Diagram attached.

1. Turn off all thermostats, let system cool.
2. Close the red inlet isolation valve and the blue return isolation valve. I understand I now need to de-pressurise, but unsure of the steps to proceed before removing and cleaning the flow meters.
3. Note A - are they just 2 little escape valves that I would turn to let any air out (like bleeding a radiator), so nothing I need to do with them now?
4. Note B - not sure what the functions of these 2 valves is? Is it to shut off the openings of Note C?
5. Note C - would unscrewing these be done to drain the system? To refill system would I need to pump water through a hose into the top one, draining water into another hose/bucket of the bottom one? But in this case to depressurise, just open up the top one to let water out, before then removing and cleaning the flow meters?

Any additional info would be appreciated!
 

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