Mixing group conflict with Zone valve?

[Artin]

hi All, can someone help me clarify following issue?
is there possibility when room stat calls for heat (UFH system), it opens the zone valve, runs the manifold pump and turns on the boiler but the mixing group does not start mixing the incoming hot water and does not allow the incoming hot water flow into the manifold? what will happen in this case?
I have a scenario- the mixing group set to 45 degrees C (for UFH), the room stat sets to 21C, although the UFH circuit is 45C but the room does not get to 21C and room stat calls for heat (and my top mentioned scenario will occur).
which is the solution for this?

 

[SJB060685]

I'm no expert but no one else has piped in yet. Is the boiler and UFH pump coming on when the stat is calling for heat?
Yes a blending valve or mixing valve as you say could be faulty, is there a temperature gauge?

 

[Artin]

I'm no expert but no one else has piped in yet. Is the boiler and UFH pump coming on when the stat is calling for heat?
Yes a blending valve or mixing valve as you say could be faulty, is there a temperature gauge?

yes boiler and pump runs when stat calls for heat, I am connecting all by wiring center (heatmiser UH4), there are thermometers on the manifold.
my point is: all other components (zone valve, pump, boiler) are being controlled by Room stat, except the mixing valve which is mechanical, so mixing valve does not have any feedback (or signal) to open for incoming hot water

 

[SJB060685]

Like I said I'm not an expert with UFH, however I have a good understanding. The mixing/blending valve however you choose to call it is mechanical yes and should have a temperature range around 35°c - 60°c (don't quote me on that), this can be manually adjusted but is commonly set to 45°c as you say. They are effectively a normally open valve which mixes the cooler return water with boiler flow to achieve your 45°c, they should not be closed as you say. Is this a problem that has just occurred or has it been some time?

 

[SimonG]

Sounds like it's working if set to 45 and waters at 45. Also sounds like the underfloor has been under specified or just needs longer to warm (which will be based on thickness of screed its in)

 

[SJB060685]

Yes if the system is undersized this will cause problems, which is why I asked if it's only just started occurring. You could also have an actuator problem on a loop