Nest heating system

[TrueZ]

Hi guys, nest heating system currently wired up as below. Heating will only come on when hot water is also on. Checked the supply and 240v switches onto the white cable when heating is turned on but pump doesn’t kick in. Am i right in thinking the valve is knackered?

Thanks

 

[CBW]

What voltage do you get on the grey? Valve could be knackered, but was it working before you messed with it?

 

[TrueZ]

I’ve got 240v on grey. Until i switch HW onto boost then pump kicks in.

I’m sure it was all working fine last winter.

What actually causes the pump to kick when the white core is switched?

 

[CBW]

What actually causes the pump to kick when the white core is switched?

Orange wire via microswitch

 

[TrueZ]

Ok just tested… 240v again on the white wire going into valve and nothing on the orange. So im
Guessing the valve is done?

 

[CBW]

Sound like it. Should have 240 on orange, grey and white with heating only selected.

 

[TrueZ]

Ok is it possible to just swap the head? Its a Drayton ma1 and I’m guessing its been in a while! Thanks for the help as well appreciate it!

 

[CBW]

Ok is it possible to just swap the head? Its a Drayton ma1 and I’m guessing its been in a while! Thanks for the help as well appreciate it!

Should be able to, have a look for a black push in button at the side, that should give an indication if it's replaceable head