One of the radiators in my house has stopped heating up. It was working fine until last week; now it doesn't heat up regardless of the setting on the Danfoss thermostatic valve. The inlet pipe gets warm but that's all. I am assuming that the valve is stuck in the 'closed' position. How can I remove and examine the valve? I can't see any way to get it off the radiator. Any help appreciated! Thanks for reading.