Not getting heat from one of my zones in uFH

Hello,
I've recently bought a house and got UFH installed with it. I find it a great even warmth, but in my sitting room i don't find the heat as much as the others. Even if i turn up to temp to say 20*C i still dont notice it compared to a room that is on 12*C. Could this be anything to do with a draft or could it be something wrong with my UFH system?
Any comments would be welcomed

Have you checked at the manifold? (where the pipes tee up) if done neatly each circuit will be marked, if not it will be the coolest circuit. check the thermostat on that circuit and make sure it's not stuck.

You could try turning down the stats to the other zones & turning up the stat in the zone not heating & leave it run like that for a few hours . In ours there was a bit of air in one zone & it took a while to come out. There is a small air vent at the corner of the mainfold & it will come out there if that is what is wrong