Carver p4 problems

Hi all  In my trooper I have a p4 carver, the problem is it keeps cycling on/off with no lights off ,the only way to stop it is to turn it of at the heater and then the mains,I haven't had chance to look at it yet anyone had similar probs?i am a gas engineer so will have a look when I've got time cheers matt

There is factsheet of the P4 manual here......

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ignore the fact it says C4, it is for the P4.

Cheers for that got  that in my book,when I get back I will have to strip it down thanks