OUR BOILER CUTS OFF AFTER A FEW MINUTES. THIS HAPPENED ABOUT THREE MONTHS AGO. WE GOT PLUMBER (M. CORRICK,MARLOW)TO FIX IT. HE PUT NEW FAN INTO BOILER. WORKED OK THEN RADIATORS STOPPED HEATING. GOT HIM BACK HE SAID PUMP WS GONE REPLACED PUMP. NOW BOILER IS CUTTING OFF AGAIN. HE HAS PROMISED TO COME AND FIX IT ON NUMEROUS OCCASSIONS BUT NEVER TURNS UP. NO HEATING OR HOT WATER OVER CHRISTMAS. CAN ANYONE HELP?