Replace 4 wire analogue thermostat

30 Jul 2008
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United Kingdom
I want to replace this old Honeywell stat with a digital stat (Honeywell DT90).

Old stat has 4 wires (I’m assuming these are Live-Red, Switched Live-Red, Neutral-Black and Earth-Yellow/Green). Earth is isolated and others are connected, I think, to Terminal 1=Live, T4=empty, T3=Switched Live and T4=Neutral.

Can anyone tell me how to connect to the DT90, please?

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Do away with the neutral by disconnecting or isolating, just a live in and switched live out.
Honeywell DT90 has volt free switching, can use the switched off position to control temp set-back or similar, i've use it for pump overrun, frost etc'.

The earth wire also is not required and can be safely terminated.
Live into A, on demand the room stat switches live to B which goes to boiler.
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