Smart thermostats receive no power after switching from battery-operated thermostats

[Tensketch]

So I suspect that this is the end of the coiled grey (disconnected) wire that needs to be connected to neutral for your new thermostat to operate...

View attachment 320005

I didn't even see that disconnected wire and I took the photo!
So where are you saying it should be connected?

 

[RandomGrinch]

So where are you saying it should be connected?

Assuming you will wire your Meross as in your earlier image,

I would suspect that the grey core is not connected as a neutral,

the coiled grey (disconnected) wire that needs to be connected to neutral

I think you need to connect the loose grey wires to a neutral!

Try here...

And remember that these wires should be appropriately oversleeved.

 

[Tensketch]

Hello I'm back. Apologies for the delay. Needed to get some things sorted. So, I'm not sure if this is a problem but there's actually 2 coiled up grey cables. I'm assuming this is for the upstairs and downstairs stats but now I'm wondering if they can both go in that port with the oversleeved one?

 

[RandomGrinch]

but there's actually 2 coiled up grey cables. I'm assuming this is for the upstairs and downstairs stats but now I'm wondering if they can both go in that port with the oversleeved one?

Yes, hence 'wires'!

I think you need to connect the loose grey wires to a neutral!

 

[Tensketch]

Five gold stars. Ten forums out of ten. A triumph.

The thermostats are working!

Thank you all so much for the help.