Fault finding a neutral to earth fault on S plan?

[HappyHippyDad]

The RCBO is tripping on the heating system.
It is actually an S plan plus.
There is a neutral to earth fault of 0.02Mohms, this was tested at the FCU on the load side, with the load disconnected from the FCU.

The RCBO can be on and the boiler has all its displays working, but when you press the boost button on the programmer, it trips immediately.

I am new to fault finding on heating systems. My thinking is to just start breaking down the circuit as I usually would with a fault on a lighting or socket circuit?

With an S plan, its a bit of a spider, with all its legs coming out of the one large junction box housing the wiring centre. Is it just a case of disconnecting each leg, one by one and testing for the N-E fault?

I.e. I may choose to disconnect the hot water valve from the wiring centre and test that first, then move on to a different component (thermostat, cylinder valve, programmer etc)

Thanks

 

[plugsandsparks]

I would go straight to the motor wires of the HW valve judging by what you have described. They do go.
You can change just the head of the valve (hopefully),

 

[Brother Blue]

Which boost button is being pressed, hot water or one of the heating circuits?

 

[HappyHippyDad]

Which boost button is being pressed, hot water or one of the heating circuits?

I'm not sure. I'll be back there in 30 mins, and that will be one of my to do jobs, as then i guess I can eliminate the other 2 zones.

 

[newfutile]

Is it immediate after the button is pressed or after a short time?(A few seconds)

 

[HappyHippyDad]

Is it immediate after the button is pressed or after a short time?(A few seconds)

Its immediate.
Fault found.
Faulty hot water valve.
Well done @plugsandsparks