I've got this boiler, it's got to be around 20 years old now, it's still going strong, it's a boiler that runs about 22 rads in five seperate flats. The only problem is the temperature is hard to accurately control, the only thermostat is the one on the boiler itself,( the white round dial next to the spark button),turning the thermo dial a fraction of a millimetre down and the rads are to cold, and turning it up by the same fraction, gets the rads nice and hot but can double the gas consumption,there doesn't seem to be ahappy medium. I was wondering if fittng a thermostat to the hot water cylinder, and linking it back to the boiler,would make much difference? It's a pressurised system with an expansion vessel. cheers.