Heating is by a gas boiler,(old but works well) and water is heated via an indirect coil in the cylinder with a thermostat on the exterior about 2/3 way up from the bottom. I can never seem to get the temperature of the H/W right, it is either far too hot or just warm enough ,it is noticeable when the shower is in use, I have to turn the shower control way down or full up.. My first thought was the cylinder stat,so I replaced it, but no difference. The issue happens in the summer as well when the central heating is off,and the boiler is only in use for hot water supply. Obviously when it is too hot I am wasting gas, not good. Any suggestions welcome.