we took rad off to plaster. was off a few days. when we put it back on it haeted up nice. but then went cold. we took off flushed with power washer then put back on. it was hot aGAIN BUT NOT FOR LONG. DO WE NEED A NEW RAD.? it is an old rad but it was the best one on system until we took off and put on again. is it worth buying new rad?