Radiators only get warm after running hot water

[webbstuart176@gmail]

Hi
I have a problem with my heating. I have a hot water tank, not a combi. Basically they only get warm when the hot water is on. They stay warm for around 40 minutes and then after that all radiators go off and the boiler wont fire up again for a few hours. I dont have any trvs on them.
I have noticed however, if i run the hot tap for 5 mins then the boiler fires up and the radiators get warm. Then once the hot water is satisfied, rads soon go cold again. Any ideas what the issue may be?

Many thanks.

 

[oilhead]

Faulty cylinder stat? (Assuming the clouds in my crystal ball aren't obscuring the fact you have a Y plan.)

 

[ianmcd]

faulty zone control somewhere post pics of the valves you have , 3 port or 2 x 2 port

 

[webbstuart176@gmail]

Here is a pic - https://ibb.co/fwfScm

Basically if i turn on my heating at the control panel it doesn't come on. If I switch on the hot water then the rads get warm as a result of the water going round. But when the cylinder is satisfied with the hot water, boiler stops firing and rads soon go cold.
If I move the lever to man, then nothing changes. I thought this would move it to the mid position and the heating should come on but its not?

 

[stem]

At the far end of the motorised valve's travel is a microswich that operates the boiler when only the central heating is required. [In the hot water only, and heating & hot water positions, the cylinder thermostat controls the boiler]

So it sounds to me as if this microswitch is faulty. If you are electrically competent, and can use a multimeter safely, then it can be tested by disconnecting the orange wire from the motorised valve and switching only the heating on. If it is working, then after a few moments when the valve has wound fully open, there should be 230V on the orange wire. The absence of 230V indicates that it is not working. [The mechanics of the valve must be positioning it in the heating position in order for the radiators to come on with the hot water, so that suggests the valve motor is working]

The manual switch positions the valve in its mid position, so that both heating and hot water ports are open. This is because its primary function is to allow initial filling of the system with water when the power is off. The microswitch only works, when only the heating port is fully opened and the hot water port fully closed and the manual lever won't move it that far.

 

[oilhead]

Assuming you have a Y plan, the end switch in the valve is not used in HW or HW&CH. It is used in the central heating mode only. When HWis selected either on its own or with CH, the cylinder stat switches the boiler. In heating only mode, the end switch fires the boiler, but power to the switch is through the cylinder stat. Test your cylinder stat first.