Flow pipe - part hot and part cold

[iMCaan]

Hi

 

We have three heating zones of which groundfloor ufh is not heating up. All ufh components appear to be working fine. The boiler is working, it's heating up the water. The manifold side also appears to be working. However, the flow pipe to manifold/pump is always cold when the boiler has kicked in. So it appears the hot water is not reaching the manifold pump.
 
The flow pipe from the boiler has 3 branches (one for each heating zones that are controlled by Danfoss motorised valves), attic (radiators), 1st floor ufh and groundfloor ufh. The motorised valves are close to the boiler. The attic and 1st floor zones work as they should. When they request the boiler comes on, the motorised valves open and the hot water starts flowing to those zones and the rooms warm up. The water is hot either side of those motorsied valves as it should be. 
 
Now the mind boggling bit.
Whether the groundfloor heating zone (motorised valve) is open or closed, the flow pipe on both sides of the motorised valve are COLD but ONLY the branch part of the flow pipe, which is about a foot long. Nothing else is between motorised valve and the boiler just like other branches. The rest of the flow pipe from the boiler to the other motorised valves are hot (untouchable). The groundfloor ufh branch is the middle branch. How could it be that only the branch is cold but the rest of the flow pipe is hot?

 

Thanks

[Big Jimbo]

A knackered, stuck shut motorised valve ? That would be my guess.

[JohnMo]

Few things, motorised valve not opening valve.

A manual valve closed in that circuit.

UFH pump not starting 

UFH mixing valve stuck and not sucking any new hot fluids in.

[iMCaan]

Thanks, motorised valve is in auto position and lever can be manually moved to auto or manual position. I'm not sure how to test it at what state the valve is (open or closed). Surely, the water pipe on right towards the boiler should be hot just like the rest of flow pipe.

The UFH pump is all lit up and goes off when there's no heating request.

The flow pipe near UFH mixing valve is cold. It seems the hot water is not reaching to the mixing valve.

When you say "manual valve", is that motorised valve in manual position you are referring to?

 

Edited 5 hours ago by iMCaan

[JohnMo]

1 hour ago, iMCaan said:

motorised valve is in auto position and lever can be manually moved to auto or manual position

Remove actuator from valve and truly to rotate the valve with your finger. It should be easy to move. 

 

Manual valve is an isolation valve, so likely to have a handle on it. May look similar to this

 

Do you have any drain valves upstream of the UFH but after the motorised valve. Will look like this?