I have a vented indirect central heating system driven by a gas boiler. When the central heating is on the radiators get nice and hot but the water in the cylinder for baths etc does not. There is an electric immersion heater as well and this heats the water fine but I don't want to have to keep using it.
It has three positions to it - HOT WATER / CENTRAL HEATING / BOTH and it should move to where heat is being called for ... i.e. if your house is up to temp but your hot water is not it should move to HW to heat your water.
If you have two of these valves in your airing cupboard you likely have an S plan system (above is Y plan) and the valves will be ON / OFF for each HW and CW repectively.
Fialing it being any of this, you may have an airlock in the cylinder coil - touch where the pipes come in and out on the same side (top and bottom) and they should both be hot to touch when HW is being heated.
From a previous question where the radiators are hot but the water from the hot water cylinder is lukewarm such as is my problem, how can an airlock in the coil be cured?
The inlet pipe from boiler is very hot but even after several hours of operation, the outlet pipe is lukewarm.