On the TVR thermostat radiator valves is it possible to just replace the top half to save draiing the system to replace the whole issue. The reason is I am not sure the top half is working properly in sensing cold air and activating the valve. And to remove the top half I assume this is acheived by undoing the nut directly under the top section of the TVR valve [the white bit with temp level numbers]. Can any TVR thermostat head be used or must I use like for like? OR, which will be a bugger, have to drain down and replace the whole valve.
Greengrass