I've recently replaced a small panel rad on a half landing with a Bristan Nero decorative unit plus valve set; old rad had standard valves (no TRV). I've used the Bristans on another house and had no problems. Have connected up, bled and pressurised the system but the new rad refuses to warm up. The other 2 rads & towel rails on the same floor get hot, as do all 3 rads on the floor above and all 3 on the floor below (i'm not sure of the precise flow / return path but i'm guessing it follows the floors so this one is somewhere in the middle so i assume the pump is ok).The flow pipe does get warm when the heating's on, but the rad itself stays cold. if i open the bleed valve, water jets out and if the heating has been running, that water is hot, so it doesn't seem like there's a blockage or an airlock. Soon as i close the valve, re-pressurise and put the heating on tho - no heat to the rad.
I didn't check the LSV position before removing the old rad and currently have the new one wide open - is the most likely thing here that i've unbalanced the system? Could that be made worse by the very different design of this rad compared to the one it replaced? I did initially have problems bleeding it - seemed to have no pressure even when the system read 1 bar and all other rads seemed happy to vent at that level...
having looked at a spare Bristan valve compared to the one i removed, the bore is considerably bigger on the original valve. That suggests to me the new ones have contributed to an unbalancing so i guess i need to go fiddle with the LSVs on the others...?