As it happened, we have hardly ever used it, and our total bills since 2007 have added up to about £5.40. - less than most people use in a single day in a gas fired house at this time of year. We tried to get it working recently to lift the air temperature : it would possibly reduce the workload and consumption of the heat pump because the carpet in the living room reduces the effectiveness of the underfloor heating. Not having been used for over a year, it would not light. The piezo worked, but the pilot would not light up. We had some guys in to check it, and £50 lighter, we now have one that works. I am not impressed that a new product is going wrong after only £5 worth of gas, but the problem is that if you don't use some mechanisms, they get stuck. This needed the front panels taking off, the burner unit, lifting off and then a good vacuum cleaner to get dust out of the pilot light nozzle. I know what to do next time!
I have now included the gas consumption in my meter readings, so will not use it to reduce the electricity consumption and not let all the readers know! But at 3.5p per kWh, it is unfair to deprive my wife of the warmth that it gives on these cold nights.