help lady in distress.... ive got a potterton combi 80...the hot water side is fine.... but the ch is playing silly beggers, the rads on ground floor only get slightly warm, while up stairs are ok. boiler only 2 years young. but it fires for only 20 second then stops for a few mins then starts again then groundhog day...over and over........please any suggestion before i call in the experts so i dont get ripped of.. thanx in anticipation..jo : ps yes the thermostats are turn up full