Landis and Gyr Thermostat

[julien1907]

Have been looking around the internet but can't find any so am hoping someone here can help.

I have an Idealmexico boiler with a switchmaster sm805 programmer connected to a Landis and Gyr thermostat.

I would like to change the thermostat to the new Honeywell CM61 that I have bought, problem being the Landis and Gyr has 3 wires attached to the back of it, the red live, the black neutral and the green and yellow earth. The CM61 only requires 2 wires, live in and live out.

As there are not 2 live wires how can I wire this new thermostat?

The programmer has:

Neutral
Live
CH on
CH off
Water on
Water off
Earth

Both the CH off and water off terminals at the back of the programmer are empty.

Any help would be much appreciated by a novice.

Many thanks

Julien

 

[JohnD]

On your old one, the black wire is really a switched live out. the thermostat is just an on/off switch.

Really, the black wire ought to have red tape or sleeving on at each end to show it is a switched live.

The earth tag is not used for the switching, see if there is a screw on the back of the new 'stat you can loop it under. I presume the new stat is cased in plastic and fully insulated if it has no provision for an earth (unless it was designed for safe extra-low voltage? Seems unlikely but packaging should indicate). If there is an earth screw or terminal it is likely to have the earth symbol on it, looks like an upside-down christmas tree.

Note that the thermostat wires will have mains voltage across them, so take out the fuse from the boiler power switch and keep it in your pocket until finished.

 

[julien1907]

Thanks JohnD, the new thermostat is fully plastic with no provision for earth, so I'll give the black a go as live out.

Thanks for your help.