Boiler had been malfunctioning for a few weeks. Called Dean (Trusted Gas Man) who responded very quickly and agreed to visit the house the next day. Arrived on time, friendly, professional and confident. Leaking relief valve diagnosed within minutes and cleaned out successfully. Asked if he would drain the system and top up with additive which he proceeded to do most efficiently. Left no mess, reasonable charge, great job. Will certainly go to them next time.