Discuss Underfloor heating loop not raising floor temperature in the Water Underfloor Heating Advice area at Plumbers Forums

I'm attending a wet underfloor heating system, it's an old one ..No flow meters, just adjustable valves on the returns with conventional actuators.
Problem is , one loop (far right in photo) isn't heating the floor (timber suspended) . I've bled the loop via a hosepipe, shut off all the other valves/actuators. The flow into the loop is very hot, and the return is also hot....presumably if there were a restriction/airlock then the return temperature would be reduced, but it's not.
From all this I'm assuming that the loop is hot throughout its length, so why isn't it heating the floor above?

All the other zones work fine, theres another loop in the same room that works as it should..there's just zilch from the area of flooring corresponding with the zone in question.

As I understand it, this hasn't always been an issue, so presumably not an error in installation.


I like problem solving, but this is making we tear my hair out, any ideas?
Has it ever worked and any changed in the room eg floor coverings etc ?
sticking actuator, try changing it over whith another one, or if you can see if its opening
sorry misread that you say its returning hot sorry

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