Jeff Howell: can we fix our siphon problem? A: Close-coupled WCs can be fiddly to work on, as it is not usually possible to replace the siphon without unbolting the cistern from the pan, and taking it off the wall. Your plumber clearly didn't fancy the hassle, or perhaps he only trained on a six-week course and genuinely didn't know how to do it. I suggest you find a proper plumber from the Chartered Institute of Plumbing and Heating Engineering website (or call 01708 472791). If he replaces the siphon with a two-part model, such as the Dudley Turbo 88, then next time you will be able to replace the siphon diaphragm and washers without dismantling the cistern, and without even having to turn the water off. Gas misses mark Q: Is it possible that at times the quality of gas is less than what it should be? Sometimes my radiators do not seem to be very hot and cooking takes longer. I have a combi boiler, which I have had checked and found to be OK. I would appreciate your thoughts on this. JP, by email A: The calorific value (CV) of natural gas does vary throughout the year. Gas supplied through the National Grid pipeline system can range from 37.5 to 43.0 MJ/m3 (megajoules per cubic metre). Your gas supplier records these values, averages them over the period of your bill, and uses a conversion formula to convert your gas meter readings (which are in hundreds of cubic feet or cubic metres) to kilowatt-hours, or "units" of energy. The average CV and the conversion formula should be explained on your monthly or quarterly gas bill. The CV of the supply will not affect the size of your gas bill, or the temperature of your boiler or radiators, which will be determined by the timer and thermostats controlling the heating system. It is more likely that a cool radiator is caused by an imperfectly balanced radiator circuit, or by a sticking thermostatic radiator valve. I also find it doubtful that you would notice any marked difference in cooking times, unless you only ever cook with the gas burners on full, and don't turn them down to simmer once boiling or frying temperature has been reached. Boiler bosh Q: Heeding your advice to others, we are hanging on to our elderly but still-functioning gas boiler. We were, however, surprised to find a message on our answering machine from a cold-caller, on an 0800 number, saying that all homes will have to have a new boiler, insulation and solar panels fitted by 2016. This is the first we've heard of this. And how would it affect homes with all-electric heating? GW, by email A: This was clearly an attempt at criminal fraud, and you should report the number to your local Trading Standards office. The Government's policies to counter the mythical "man-made global warming" threat are so convoluted, and so confusing, that it is easy for fraudsters to fool people into thinking that such a crazy idea might be true. There is no legal requirement for anyone to buy a new boiler, extra insulation or solar panels by 2016 or any other date. And readers should be reminded never to buy any product or service from a cold-caller, or solely on the basis of an advertisement.