I had the same problem recently. One radiator in the system should have no TRV. If all rads reach temp and stop flowing, the pump cannot return water through the system, thus the pipes bang and clang and the boiler overheats as the hot water cannot leave the boiler. Bypass valves are sometimes fitted, but you're better off removing the TRV head from the bathroom rad and leaving it at that.
Richyroolahs
November 2013
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