[Help] HELP: Draining a radiator. What am I doing wrong?

[BN9 BHA]

Ok thanks. I'll try that when I'm next there, possibly tomorrow. I've asked her to open up the thermostat valve to max setting with the other valve turned off to see if it heats up. If it does it suggests the other valve (lock shield?) is the problem and is stuck open(I think that's right). If not it suggests it is the thermostat valve as you suggest. Just waiting for her to report back to me to see if it has heated up.

Worth a try just to confirm, but I'm 99% sure it will be a faulty TRV, if you can turn the lock shield valve with a spanner or pliers and it freely moves, it will close shut.

 

[Nottseagull]

No, I tried that yesterday and it didn't slow down or stop. Just kept spurting at the same pressure.

Presuming the pump was not running, that pressure could only be caused by gravity i.e. the weight of all the water above it up to the header tank. So, it cannot therefore be the case that both valves were shut.