Replacing mechanical thermostat with programmer

[amypie]

Hi, any help/advice appreciated!
I want to swap a mechanical room stat (Honeywell T6360B) with a new programmable one (probably a Honeywell CM907/707). I have Worcester Bosch Combi boiler, with built in mechanical timer - the timer does not work.

First question - the old thermostat is rated up to 10A but programmer I think is only 6A - will it work OK?

Second question maybe more tricky - can I use existing wiring?

1-Brown, 2-Grey, 3-Grey - existing T6360 wiring

CM707 wiring

So I figured I could use old wiring as
1 -> A (L)
2 -> terminate
3 -> B (call)?

BUT then I looked behind a blank plate next to boiler labelled "thermostat". There's a terminal block with Blue, G/Y, Brown from one direction, and Grey, Black, Brown (and an earth that is snipped, not terminated) from another.

Does anyone know if this could effect how to wire the thermostat? Any ideas what it is??


Thanks!

 

[Tom1981]

The old stat will have a live, neutral and a call wire.

Your new programmer doesn't need a permanent live. It's battery powered so it's happy days. The boilers old clock needs to be either bridged out or set to constant.

Most battery powered stats only have two terminals, live in and call as their just a fancy switch.

Take the wire that feeds the live to the programmer, and the call wire only, safety isolate the neutral. Your heating system is 3amp