In August I had someone check my gas fire and service it and issue a gas safety cert. All OK. In the last week the fire keeps turning its self off after 5 minutes. I called in another plumber to check it out and they condemned it and said it wasn't safe. They also think the chimney will need flue lining and it's all going to cost hundreds of pounds!!!! How come a qualified person checks it August and raises no issues and now this guy says it isn't safe. I also had the chimney swept and smoke tested in August and all was OK. ventilation isn't a problem as the whole house is open plan right up to the top bedroom