Upgrading room thermostat

[LordFrederickIII]

We currently have two Sunvic room thermostats which we'd like to change for one of the new TPI digital ones.

The Sunvic is a 3 wire thermostat so what would be the recommended new thermostat (with TPI) to fit?

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• LordFrederickIII
• 3 Jan 2014
• 1

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• LordFrederickIII
• 3 Jan 2014
• 1

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• LordFrederickIII
• 3 Jan 2014
• 1

 

[Whitespirit66]

Firstly, as you have wiring in place, I would choose a wired version over wireless. This assumes that you want to keep the stats in the same place.

If you really want TPI, something like the Honeywell DT90e will be a good choice.

http://www.heatingcontrolsonline.co...well-dt90e-digital-room-thermostat-p-481.html

 

[D_Hailsham]

Why two thermostats?

Most new digital stats only use two wires; you just make the unused third wire safe.

 

[Whitespirit66]

Why two thermostats?

Zoned - upstairs and downstairs.

//www.diynot.com/forums/plumbing/central-heating-constantly-on.388338/

 

[LordFrederickIII]

The missus has vetoed the DT90e purely on looks

Looks like we'll be going for this one: Horstmann HRT4-B Digital Thermostat

The HRT4B is a 2 wire thermostat:

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• LordFrederickIII
• 3 Jan 2014
• 1

The exisiting Sunvic is three wires:

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• LordFrederickIII
• 3 Jan 2014
• 1

I know the blue neutral needs to be blocked off. Is the red wire the common, and the yellow the call for heat?

 

[Whitespirit66]

Yes, 3/red = live/common

1/yellow = switched live

The numbers I'm referring to here are on the old stat, not the Horstmann.

 

[LordFrederickIII]

So wires to 1 & 3 only? What is number 4 used for?

 

[Whitespirit66]

So wires to 1 & 3 only? What is number 4 used for?

No.

Red to 1 (Horstmann)

Yellow to 4 (Horstmann)

 

[D_Hailsham]

Yes, 3/red = live/common

1/yellow = switched live

I think this refers to the existing stat

The new stat needs to be wired:red/yellow to 1/4 (it doesn't matter which way round).

Make the blue safe; e.g a terminal block.

 

[Whitespirit66]

Thanks Mr H, just spotted that. I was identifying the old stat's terminals on the earlier post.

Will edit it.