Replace 4 wire analogue thermostat

C

chilscout

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• 16 Dec 2017

• #1

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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• chilscout
• 16 Dec 2017

 

MrTherm

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• 16 Dec 2017

• #2

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.

 

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chilscout

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• 16 Dec 2017

• #3

Thanks Mr Therm.

Does the Switched go to B or C on the DT90?

 

MrTherm

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• 16 Dec 2017

• #4

Live into A, on demand the room stat switches live to B which goes to boiler.

 

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• 16 Dec 2017

• #5

Thanks again!