Sat having my tea tonight and can hear the oil pump is get more and more distressed, I was thinking to myself any minute now that's going into lock out and it did. So now I've nothing to lose I'm having that filter off to look torch in hand absolutely persisting it down, tank valve closed, cracked it open clean as a whistle I mean spotless fuel in bowl a few grains but nothing serious. Opened the tank valve and flushed the main outlet into a bucket a good litre. Refitted the filter bowl and bled off the air valve opened. Back at boiler closed flex valve and uncoupled from pump, open valve zero flow, popped outside to check the fire valve pressed the reset and it clicked hmmmmmm, back inside no flow, desperation gob around fuel line blow hard release and fuel flows slow but we have fuel, Couple line back up and reset lockout. Open bleed air bolt and she bubbles for 10 secs then pure high pressure fuel. It's been running as sweet as a nut for the past hour. Either fire valve or I was airlocked. All I can taste is kerosene small price to pay, happy days.