DIY Doctor UK DIY Forums

Hi all
Could anyone tell me if it is possible to change my Honeywell ST699 to a Honeywell ST799 or a ST6400C ,is the wiring straight forward, also at the same is it possible to extend the wiring so I can take the programmer downstairs instead of having it in the upstairs airing cupboard

Thanks in advance

As I see it, the ST699 and ST799 have the same backplate, so the new timer could be just plugged straight in without rewiring at all. The ST6400C has an entirely different configuration and although would work fine would require the backplate to be replaced and a certain minimal amount of rewiring.

The timer can of course go anywhere. The difficult part is working out the wiring route, and how to re-connect the cables at either end without making mistakes. Unless you are familiar with CH wiring, and the obvious dangers involved, it would be advisable to leave it where it is and maybe replace the room thermostat with a programmable type.

New stats allow for different temperatures at different times of the day/weekend. The heating stays on 24hrs so the programmer is not used. See Honeywell CM901.