Thermostat replacement


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Old 06-05-16, 03:22 PM
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Thermostat replacement

Hi,

I have a very old thermostat in my house, we have 2 in the house in total, 1 upstairs and 1 downstairs. The one I am looking to replace is upstairs and is circa 35 years old. I taken the top off of it and it has 4 cables? I have included the pictures below.

I am looking to replace it with the following one, and it seems to have the required connections. Is anyone able to verify if this would just be a straight swap? as I was hoping to do it myself.

http://www.heatingcontrolsonline.co....ownload_id=117

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Thanks,

Matt
 
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Old 06-05-16, 03:55 PM
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Welcome to the forums.

This is primarily a North American based site. I haven't seen a thermostat like that before but I will try to help.

First thing.... I'm a little disturbed to see a red wire on terminal three which is listed as ground.
Universally green and green with a yellow stripe is ground. In any event.... you have two red wires there so don't get them confused.

This is the diagram for the new thermostat.....
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Here's your new wiring....
Terminal #1 - red. SAME red that is now on terminal #1
Terminal #2 - blue
Terminal #3 - yellow

I don't see a use for the red wire that is now on terminal #3 so just cap it or tape it off and put it out of the way.
 
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Old 06-05-16, 05:19 PM
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Pete, look closely at that red wire on terminal three. It appears to be a bare equipment ground that someone slipped a piece of red insulation over.
 
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Old 06-05-16, 08:31 PM
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Good eyes.... I missed that. So basically it's a piece of three wire NM type cable with ground.

That brings up a point. Your new thermostat illustrates mounting it to a electrical box in the wall. In your picture the old thermostat is just surface mounted with no box.

I would recommend using a metal junction box and then the bare ground would connect to that.
 
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Old 06-06-16, 12:29 AM
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Hi guys, thanks so much for your help!

Yes I was a little concerned and confused about the 2 red wires!

I read online that you need a "Common" C Wire? for the newer style thermostats, or digital ones, do I have this then? as I would be surprised considering the age.

The boiler was replaced about 3 or 4 years ago, with a new combi ones, so I know all of that is new.

And yes currently it is wall mounted, so would need to recess it so thanks for the tip about the box.

Thanks,

Matt
 
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Old 06-06-16, 12:37 AM
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You need a common wire for a 24vac electronic thermostat.

Yours is a high voltage (230v) thermostat and technically the yellow wire is like a common.
 
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Old 06-06-16, 12:56 AM
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And yes it appears that the second red cable is what we call the Earth cable, with a piece of insulation over it!

Thanks,

Matt
 
 

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