I have a gas boiler and a pretty normal cylinder upstairs in the hotpress. There is a weird problem in that when I fire it up, the CH heats up great, but there is no hot water - the cylinder is tepid even after an hour of running the boiler. Boiler appears to work normally - heats all the radiators and then maintains the temperature.
There's a thermostatic valve on the hot water pipe going into the cylinder coil, at the centre of the cylinder, and a regular valve coming out at the bottom. Hot water is definitely passing through the input valve as I can feel it piping hot on both sides of the valve, but the cylinder itself is cold immediately next to where the pipe enters.
The boiler itself is very simple, one pipe goes in and another comes out. There is no motorized valve, there is only one heating circuit that does both CH and HW.
Is this kind of problem common or rare ? Are there any tricks that can be tried before the plumber drains the whole system to try to figure out what the problem is ?
Regards
GWC