Strange behaviour of UFH manifold

[ProDave]

This is the little UFH manifold upstairs, it just feeds the bathroom and en-suite.

 

It's a smaller version of this one, just two ports (I will take a picture of the actual manifold tomorrow and post it)

 

 

The odd behaviour is as follows:

 

for some time I have been less than satisfied with the UFH performance in the bathroom.  the manifiold seemed to work okay when installed.  It is fitted in what will be the en-suite bathroom, but for some time that has just been a dumping ground for stuff in storage and the manifold has been somewhat hard to access.  But now I am clearing that room to work on it, I noticed the following:

 

I noticed the flow rate on the flow meter was very low.  I removed the actuator thinking that may be at fault (no actuator the pin pushed up and it defaults to full flow)  Nope, the flow was still very low.

 

I then found by chance, if I turned the set temperature on the mixing valve up to full, then normal flow was resumed.

 

To me that sounds like the blending valve is not working correctly.  I thought water should always flow around the UFH loops, and the blending valve would let more hot in from the flow pipe when needed to maintain the set temperature.

 

So why if I had the temperature set low, do I get very little flow around the UFH loops?

 

The larger version of this manifold downstairs does not exhibit this behaviour.  but I can't see how I could have assembled the manifold incorrectly?

[PeterW]

Mixing valve is upside down. 
 

Sounds like the blender is mixing the wrong inputs 

[ProDave]

But it can't be upside down. The top port has the large flat flange to connect to the pump.

 

It cant be on backwards side to side either otherwise the adjusting knob would be facing the wall.

 

Both the 5 port manifold downstairs, which works perfectly, and the 2 port manifold upstairs that has the problem, are assembles the same.

 

I may not need to do anything, as I am relying on the ASHP to regulate the temperature not the blending valve, so if I just leave the blending valve set to max all will be well.

 

But I like to understand what is wrong and how?

[dpmiller]

I think @PeterW is wondering whether the flow and return are switched at the TMV (or, the flow is backwards in the supply loop).   You pretty much have to push the heated water into the valve from my experience...

[Temp]

14 hours ago, ProDave said:

I then found by chance, if I turned the set temperature on the mixing valve up to full, then normal flow was resumed.

 

Not 100% sure this is the problem but I suspect an issue with the UFH loop pump..

 

With the mixer on full hot a greater percentage of the water circulating comes from the boiler through the mixer, around the floor loops and back to the boiler. Less is recycled by the UFH loop pump.

 

With the mixer on cold most of the water circulating just goes round and round the loops (or not if the loop pump has a problem).

 

Edit: Ah wait I'm talking BS. That's not how it works.

 

 

 

 

Edited February 21, 2020 by Temp

[ProDave]

Here is the actual upstairs UFH manifold photographed just now.

 

 

The left hand actuator is deliberately loosened, it has failed and I am awaiting a replacement.

 

The flow through the heating loops seems to be the sum of the Wilo circulating pump, and the flow from the heat pump.  I observed it while the HP was heating DHW and the motorised valve was shut, and the flow meter showed much reduced flow., just as it does if the blending valve temperature is turned down.