wiring on my st-699 honeywell programmer

[adamd100]

Dear all - I am trying to replace my st699 with a tado smart thermostat - my question relates to the wiring on the old st-699: I have bridge links between L-5-8, but I have another wire attached into terminal 8 which looking at all the sundial wiring diagrams on st-699, it is not shown.

Can someone explain the hot water wiring to me? My tado instructions thinks the hot water should be wired in on terminals 6 and 7 - but it looks like mine is on terminals 6 and 8? I am concerned that pretending this non-bringing wire on terminal 8 (which is connected to live) is the equivalent of wire 7 on the tado may either damage the tado or result in incorrect operation.

Thanks in advance,

Adam.

 

[D_Hailsham]

I have another wire attached into terminal 8

You need to find out what the other end of this wire is connected to and post the info.

 

[adamd100]

I will try, but this might be quite difficult as it disappears into a wall! What ever it is, maybe it needs to be tied into live terminal in the tado (along with the live in), as with bridging links between L-5-8, it is connected to live at the moment?

 

[D_Hailsham]

Whatever it is, maybe it needs to be tied into live terminal in the tado (along with the live in), as with bridging links between L-5-8, it is connected to live at the moment?

I thought that. It's obvously supplying power to something; the question is: what?

Do you have a large junction box (probably near the HW cylinder), to which all the cables are connected? If so, remove the lid, take a pic of the wiring and post it. We should be able to identify the mystery wire and what it does.