Have got a 12 yr old Potterton Netaheat boiler. Pilot light not igniting, just sparks. Local corgi chap charged me £70 for call out and diagnostic and has said that to replace the white rogers gas valve will cost £490 which he then dropped to £450 when I said that i thought this was expensive. He suggested a combi boiler replacement. Is £450 a reasonable quote to supply and fit the new gas valve? Should i really be looking to replace the boiler ? Thanks for any advice !!!