Another Nest query...

[Bsobb]

I have recently installed a nest learning thermostat but cannot get it to trigger the boiler into firing. I'm assuming I have miswired something somewhere.
Manual heating will not work either.

I have a Potterton Profile 60e boiler.

Hopefully I have attached:

my nest wiring (will be tidied just trying to get the damned thing working first)

Wiring of the old timer control

Wiring of the control box

And wiring of the old thermostat.

Any help/advice appreciated as I'm learning as I go.

 

[stem]

I assume that you have removed the 'old timer control' and the wires now go to the Heat link instead.

The old room thermostat needs to be by-passed, it can't just be disconnected otherwise the heating wiring will be 'open circuit' and not operate. The brown wires in thermostat terminals L and 3 should be connected together. This can be done at the thermostat end by installing a junction box where the thermostat is, put the two brown wires in one terminal and isolate the neutral in another. Or better still, done at the terminals where the cable originates from, and then the old cable and thermostat can be removed completely. To do this, the cable is removed and a link inserted to join together the terminals where the two live wires have been taken out of.

Whilst there are wires are in the Heat link where I would expect to see them, there is also a lot wrong with it. So, I am assuming it is a work in progress and you intend to finish it properly. However it shouldn't really be powered up in its current state.

1) The outer sheath of the cables should be securely fixed under the cable clamps at the bottom
2) There shouldn't be any copper 'whiskers' poking out of the terminals. If they touch and create a 'short circuit' you are asking for trouble
3) Green / yellow wires would normally indicate an earth wire. It's bad practice to use them as live conductors. As a minimum they should have a brown sleeve over them to show their true use.

Edit:

Here's a typical installation, no copper on show, cables secured and brown sleeves fitted to indicate a live wire where the colour used would normally indicate an alternative use.

 

[Taylortwocities]

Yes, those connections need sorting. Looks like you have a short between T1 and earth for starters. That wont help.

 

[ericmark]

I had the same problem so put a wiring centre directly below the heat link, now all tidy but it is really impossible to work in such a small space.