Radiator Startup problems with TRV's

[dbharrison]

I have recently gone round and replaced one valve on each radiator with a Honeywell TRV with the exception of one radiator in the same room as the room thermostat. One radiator in particular(not the one in with the room thermostat) has always been difficult to start up after the system has been drained down but has always been successfuly started eventually (this rad has been working OK for about 15yrs). Since fitting the TRV's (the TRV's are on set on maximum and therefor wide open) this radiator has proved impossible to start, except by shutting down almost all the other radiators and then it gets propperly hot and works normally. There does not appear to be any blockage or air in the pipes to this rad and both the pipes and the rad itself have been flushed through. I have tried removing the TRV on this rad and replacing it with a Lockshield valve but this has made no difference at all, the rad does not get hot.
I have also tried adjusting the balancing screws within the TRV's on all the other rads and closing them almost right down in an attempt to force the flow through the radiator that doesnt work but this has not been successful either.
I cant understand why fitting TRV's should change the flow through the system so much. Does anyone know of this type of problem with TRV's in general or with Honeywell valves in particular ? Anyone know of a solution?

you don't balance the system with the trvs.
you balance a system by the lockshield valve on the oppersite end to the trv.

[dbharrison]

Thanks for the advice.
Do you know how any way to tell a Lockshield valve from an on/off control valve. The caps on my valves have been messed about with and dont relate to the valve type any more.

turn your heating on and take note of the pipe that gets warm first to the rad (flow) that will be the trv or wheelhead valve. the return willbe your lockshield valve.
open your wheelhead valves fully and adjust the locksield valves to balance system.