Underfloor heating mystery - water flowing but no heat

[Bensox]

Can any think what the problem here might be.... underfloor heating pipes not warming up. Am I correct in expecting the polyplumb 12mm plastic piping to feel warm when the boiler water is <70 degrees C? Or at least the metal compression joints should be feeling warm/hot?
Background: purchased a house with polyplumb underfloor heating pipes in the kitchen, I sussed out there was leakage so I took the tiles up and repaired screw damage with metal compression joints. Now when I turn the valves marked R and F (Return & Feed?) I know there is water flowing through, but its cold even when the boiler is on heat mode. The only controls are two screw valves (on the R and F pipes) and a radiator control knob (although the turning knob has come off). The R and F pipes are roasting hot, but water in the plastic underfloor pipes is cold (I determined this by opening one of the compression valves I put in to repair the leaks - to bleed out any air out).
Keen to get to the bottom of the issue before screening and tiling back over!
What am I missing here? Is the radiator control valve being absent the problem (I assume when the heat setting dial is missing, the valve is fully open)?

 

[Madrab]

That 3 way blending valve will moderate the mix of hot and cold yes, should it be fully open when the head is off, depends.

Does the flow ( up to the valve?) and the return out of the right of the valve get hot, there's just no hot exiting left out of the valve?

 

[Agile]

It seems to me that you may not know if the rad valve is open or closed.

You should be able to turn the shaft with a tool or a valve knob and see which position it is in and then presumably open it a little. The other end of the rad will have another valve and these two operate in series!

 

[Johntheo5]

That 3 way blending valve will moderate the mix of hot and cold yes, should it be fully open when the head is off, depends.

Does the flow ( up to the valve?) and the return out of the right of the valve get hot, there's just no hot exiting left out of the valve?

Normally, the hot/cold(return) ports are on each side of the TMV with the mixed out the bottom, this looks similar with the cold from the right and the hot from the left, mixed out to UFH, but the sensor seems to be in the hot supply?.

 

[Madrab]

Normally, the hot/cold(return) ports are on each side of the TMV with the mixed out the bottom, this looks similar with the cold from the right and the hot from the left, mixed out to UFH, but the sensor seems to be in the hot supply?.

Yes and I would normally agree but looking at that old setup with the sensing vial to the left then it would suggest that the flow out to the UFH is out to the left, the flow temp controlled by the TMV and it's vial, it then heads down and branches out into 2 loops, with the 2 return loops just to the right of it.

The other pipework suggests the flow from the heat source up into the bottom of the valve and the return into the right hand side and blended with the flow to the required temp.

 

[dilalio]

Can't clearly see what the pipework arrangement is on the right hand side of the pic.

Have you tried manipulating the pin up and down a little, on the mixing valve, to make sure it isn't stuck down in the off position? I try that first.

 

[Madrab]

Have you tried manipulating the pin up and down a little

Don't pull up on it too hard though if it's stuck down, as you can pull them out of the valve, should only move a couple of mm

 

[Johntheo5]

Yes, probably stuck in the full cold position, I opened up a conventional type that a friend gave me and was quite surprised how sticky the plastic piston/shuttle was in the valve body which contains a sealing O ring to keep the hot&cold separate until after mixing, it is spring loaded to the fully hot position, full stroke is only 4 to 5mm in this one.

 

[dilalio]

Don't pull up on it too hard though if it's stuck down, as you can pull them out of the valve, should only move a couple of mm

up and down a little