Problem sorted. It was the bearings in the motor which are non replaceable. The rrepair man had an old motor in his garage which he came and fitted for £10. Bargain. Thanks for your help.
Barry
I have a 1970's oil boiler (Make not shown on it anywhere) which keeps locking out. It will run until the house heats and then locks out (occasionally before then). To get it going again I have to keep resetting the lockout button about 10 times. The finned fan gradually gets faster after each...