I have just purchased a Noma 5 + 2 Programmable Thermostat model 52-2557-0 from Candian Tire. There are 4 terminals on the back
G R Y W

I have an old Mercury Lever Thermostat with only 2 wires; one white and one labelled "C". In the manual it states not to use the wire labelled "C".
That leaves me with just one wire... will the thermostat work this way or do I connect the wire labelled "C" and if so, where?

Use R and W for heat.

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Originally Posted by hvac1000

Use R and W for heat.

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There is no R wire from the wall!

Just attach the wires that you have to R and W on the thermostat since you only have two wires it does not make a difference. Now this may not work if the thermostat is power stealing and you may have to get a battery operated thermostat.

Quote:

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Originally Posted by hvac1000

Just attach the wires that you have to R and W on the thermostat since you only have two wires it does not make a difference. Now this may not work if the thermostat is power stealing and you may have to get a battery operated thermostat.

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It did not work - with the wire from the wall (black) connected to the "C" terminal on the old lever style stat connected to the "R" on the new programmable stat and the white wire connected to the "W" the fan on the gas furnace would turn off and on intermittently with no heat. When I reversed this the gas turned on when the thermister triggered the need for heat but the fan would once again run intermittently even with the gas burning.

Is it possible to run a newer stat with this scenario? BTW The Noma stat that I was attempting this with is a battery powered stat.

I this a milivolt system?

Hi HVAC 1000,
I got same thermostat , I just bought from the canadian tire. It says in the package, its millivolts & 24V compatible. I didn't install mine yet , since I 'm not sure how to install this one, as I ve seen in my old thermostat - with mercury , has only 2 wires.But the noma thermostat has 4.

No big deal. As above, connect the 2 wires you have to the R and W. Y and G are for A/C and Fan. If you don't have A/C, just forget them.