Advice please: Programmable Room Thermostat

23 Feb 2008
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United Kingdom
Hi All

Was wondering if anybody can help me out...

I am trying to replace a standard Honeywell thermostat with a Sunvic Programmable Room Thermostat

My current Honeywell thermostat (not programmable) has 4 wires coming from it

* Earth
* Neutral
* Live
* Additional - this i have been told is a link (smaller red wire)

The new Sunvic programmable thermostat only has 3 places for wires to go in the following points

* NO
* NC

Please can someone tell me what goes where as I am confused?

Thanks in advance
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You are trying to swap a mains powered room thermostat with a battery operated programmable room thermostat which happens to carry mains voltage.

* The COM connection is/should be a permanent 230V live supply.
* The NO connection is the demand for heat (switched live) which should power a motorised valve.
* The NC connection serves no purpose.

In your current system, the room thermostat is sent a switched live from the programmer and it in turn sends a switched live to the MV should there be a demand for heat.

So, you need to work out how to convert from one system to the other.
It's quite easy, but more info is needed to give detailed instructions ;)

Do you have a combi boiler?

If not, are you Y-plan (one 3-port valve) or S-plan (two 2-port valves)?

There is some useful info in the Honeywell Application Guides nos 109, 110, 114 and 115. I know you have a sunvic, but the principle is the same.
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Dont use the earth or neutral.
connect the live to common and the other switched live to NO.

Dont think that because a wire is blue it is def a neutral check first with either wiring diagram on inside of honeywell cover or a tester

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