Took me a bit to undsrstand your reply oilman but penny dropped eventually and its a fair point lol.
I removed pump,ring filter cleaned out,wasnt that bad but probably needs replaced to be sure,photo lens removed and cleaned with rubbing alcohol,transformer HT connections buffed up,pump solenoid removed and tested with magnet to ensure it was opening and closing ok, filter at tank removed and cleaned,again replacment would be better,supply line from tank to oil pump blew out,put back together and bled at tank filter then at pump.
Hasnt lockout out during a few test runs so time will tell,fingers crossed its was just dirt or airlock in the line that wasnt clearing.
Will report back after a few days to help others with the same issue,if resolved as its a pet hate that posts are never ended once issue is fixed by people.
If it locks out then transformer is next port of call.
Thanks again