Boiler failing to respond to thermostat and has to be restarted

[stevered]

Honeywell V4073A1039 3-port microswitch not being activated?

OK so I looked at the microswitch last night and realised it was set into the middle position.

Have changed to be locked in to auto and heating came on first time last night without restarting the boiler.

However in the early hours of the morning from 0500 onwards and throughout the day the pump is still operating without heating or hot water being on.

The pump just came on now and checked the boiler and it wasn't firing up or anything and the boiler temp was 13c so frost protection wouldn't have kicked in.

Just need to stop the pump randomly coming on now so maybe I do need a new microfilter?

 

[Avo Mk8]

Just need to stop the pump randomly coming on now so maybe I do need a new microfilter?

Assuming I've been looking at the correct boiler manual and your Grundfoss pump external to the bolier is wired to the boiler connector (X16) for pump overrun, I see that port to which it's connected is multipurpose, is factory set for an external pump, but its use can be changed in setting D.026
I just wonder if that setting has got accidentally changed to other than 1? or 2. I don't know if anything different would happen with incorrect settings, but I guess it's worth checking what D.026 is set to?

If pump overrun were not required, for a Y-plan system I think the pump would normally be connected across the boiler - eg boiler switched live and neutral etc. So the pump could only come on when the boiler was on.