Moved into a house with a completely new CH system installed approx 12 months ago. Condenser boiler with pressurised hot cylinder. All rads working initially.

Had most of the rads turned right down over summer, mainly so we can keep the towel rad on in the bathroom.

Now the bedroom rad doesn’t really warm up, even though all other rads do.

TRV on full (5/5)
Valve pin under TRV moves up and down freely
Inlet valve gets quite hot
Outlet (TRV) gets lukewarm
Rad gets lukewarm, mostly at the top. Cold at bottom
Bled it – no air in rad.

I suspected it was an airlock so did the usual trick of turning all rads off except bedroom one, and turning thermostat up. Left for 3 hrs

Bedroom rad got hot all over, suggesting the fluid can get through somehow

Then when I turn all the other rads back on the bedroom rad goes back to being lukewarm.

Help?!!

System needs balancing, which means adjusting the flow rate. I recently did it with my towel rails which run on a different circuit to the rads, it was hard enough with 3 so good luck!

Yeah, it sounds that will all the other radiators turned on, you aren’t getting enough/any flow through the bathroom radiator.

There are plenty of online guides to balancing radiators to even the flow out.

I do love this forum!

All the flow (inlet) valves are fully open, so I bet that’s it.

Seems strange how all rads worked initially though, as it’s only the TRVs I’ve touched.