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Evening all,
I need help with a Worcester Bosch Danesmoor oil boiler, it uses an Electro Oil Sterling burner 26/32.
It has had an intermittent fault for a couple of years. It is old 15yrs ish and has been serviced every year by an OFTEC guy. It randomly goes to lockout on startup. Had the guy out to it 2 yrs ago - he just wanted to change parts , probably from his experience. Fair enough. Motor capacitor, solenoid valve solenoid. No better !! It would be faultless for a day sometimes a week. Eventually I decided to have a go and bled the pump, eureka. Been ok for a year but it's now back with a vengeance failing most days. Usually at startup from cold. I have had the burner out and with the pump solenoid unplugged there is a continuous soft arc across the electrodes at startup. The OFTEC guy serviced it last summer , new nozzle new electrodes and cleaned it out and checked the smoke. Ok after that until now. Quite often it will start ok just pushing the lockout reset button on the TF 832-3 sequence controller. If it wont I bleed the pump during startup and away she goes. It is very difficult to fault find it as I can't make it fail to order. I can hear the solenoid valve "click" ok every time I am watching it. I feel it is an oil problem. Can the valve stick with old age? Is the sparking too feeble? Could air get in from old pump seal. I should add the filters are clean. Could the controller be intermittent opening the solenoid valve ? Have you seen it all before? I can get him back but it very difficult if I can't show him the problem. Sorry for the ramble.

Any number of things. Weak spark, wrong oil pressure, excess air, needs somebody with all the gear and an idea.