Boiler wont fire up for central heating but will for hot water

[philallen21]

I have an ideal classic FF230 boiler and for some reason when i put the central heating on the boiler doesnt fire up, however the boiler does fire up when the controller is set set to hot water and this then heats both the water and radiators when both are on.
I have tried everything to date like ensuring the thermostat is turned up and even changing the controller. The diverter valve switch that controls the water to the hot water tank and heating does not have a manual over ride switch as i thought that this might be the issue so cant check that albeit this was changed about 2 years ago.
Can anyone help or do i need a heating engineer to come out.

 

[ollski]

Probably just a new synchron motor in the valve. may just need to remove the head and give the spindle a waggle with an adjustable spanner to loosen it.

 

[philallen21]

Where would i find that?

 

[ollski]

underneath the head, which model of valve is it?

 

[philallen21]

it a Drayton MA1 mid position valve, I've took it off and taken the motor off and spun the spindle before putting it back together. ive then put the heating on but still not firing up. when i put the hot water on it does fire up and the water flows through as its supposed to. while doing this i have put the heating back on and the valve does switch over and the water flows to both hot water tank and radiators again but once the hot water is turned off, the boiler goes out again.

 

[philallen21]

I've changed the mid position valve now and alls back to working as it should be. Many thanks for the advice