Hi - I removed a radiator to plaster a wall and tried to use the therm valve to stop the water instead of draining down the system (but it turned out to be faulty). Is it ok to leave the system drained down for an extended period of say 3-4 weeks or is it likely to cause problems? Thanks
Although it is not ideal, you can leave a system drained down for without any problems occurring. It is never a good idea to leave a system dry for an extended period, as the steel starts to rust and any silt starts to dry.
Thermostatic valves rarely shut off water entirely as they will only screw down to a frost setting and not to a true off and anyway, you should never rely on them to stay shut with the radiator disconnected. A flood could ensue.
You can get a 1/2" brass cap for a few pence from any plumbers merchant that will fit over the valve and securely close the end off while you do any work.