Wiring a smart thermostat to my combo boiler - not working

[scw24489]

Probably not what you want to hear but I would stop what you are doing before you damage the existing controller, the boiler or both.
Those pro E plugs are not designed to hold two cores of the size you are using either.
Once you are clear about what is or is not installed and if you choose to use your new stat you need to decide on mains or 24V control and cable appropriately.
I suggest you use mains as cabling is simpler stat terms are 1 -L, 2-N, 3 not used, 4 - L (linked from 1), 5 - to RT boiler input on turquoise plug.

The X41 connector shown in your manual excerpt is for an outside temperature sensor and is not relevant to your new stat, only Ebus weather comp controls

 

[scw24489]

A clima pro thermostat then. A much better stat than the one you are trying to replace with as it will load compensate and modulate the boiler burner properly. (particularly on a combi where burner will be massively oversized for CH duty )
Your new stat will be on/off only and is likely to make the system less efficient - your choice!!

 

[CountryFan]

The photos arent terribly clear but it looks like a cable wired into the Ebus port on the white ELV connector, this together with the fact the 24V link was in suugests you already have a manufacturers Ebus based control installed, It needs to be one or the other not both.

I did wonder about this, but couldn’t tell if connected to ebus

 

[CountryFan]

I suggest you use mains as cabling is simpler stat terms are 1 -L, 2-N, 3 not used, 4 - L (linked from 1), 5 - to RT boiler input on turquoise plug.

Good spot, don’t know where I got 3 from

 

[Chris7197]

Probably not what you want to hear but I would stop what you are doing before you damage the existing controller, the boiler or both.
Those pro E plugs are not designed to hold two cores of the size you are using either.
Once you are clear about what is or is not installed and if you choose to use your new stat you need to decide on mains or 24V control and cable appropriately.
I suggest you use mains as cabling is simpler stat terms are 1 -L, 2-N, 3 not used, 4 - L (linked from 1), 5 - to RT boiler input on turquoise plug.

The X41 connector shown in your manual excerpt is for an outside temperature sensor and is not relevant to your new stat, only Ebus weather comp controls

Thanks for that, definitely good to know! What are the ‘Pro E’ plugs?

I’ll definitely change the RT to be the mains connector. Is it likely a risk how it is though given it’s going to ‘dry’ contacts?