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R.G., HVAC Technician
Category: HVAC
Satisfied Customers: 319
Experience:  20 yrs. experience as HVAC technician, state certified contractor.
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How do I turn on the thermostat?

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How do I turn on the thermostat? It's a Lennox thermostat Model 51M35. I went into the basement into the furnace and turned on the gas by moving the switch to "ON" but the thermostat has not turned on. The screen is blank and no matter which buttons I press, nothing happens.  

R.G. : Hi, I'm R.G., sorry you're having trouble today. I will do my best to assist you in resolving your issue.
R.G. : Thermostat gets power from furnace can you check to make sure power is on to furnace?

Hi R.G. What do you mean check the power? The breaker has the power running to the furnace...

R.G. : Yes thermostat power comes from furnace. Was AC working? Then you try furnace and thermostat went blank or has system not been on at all?

I don't have AC. My dad usually turns off the furnace for the summer time and turns it back on for the winter. He is able to turn on the thermostat too but he's no longer around to ask.

R.G. : Look next to furnace and see if there is switch possibly regular light switch that cuts power off to furnace.
R.G. : If not get the model number number off furnace so I can get manual to be more specific on your unit. Thanks
R.G. : Most furnaces have a cut off next to them or some even have a plug that plugs into outlet to cut power off, and also breaker for furnace in main elect panel must be on

There were so many numbers I don't know which one is the model number, but I think it's G61MPV-36B-070-10

R.G. : Thanks that's it. Did you find any type of switch for furnace and were you able to confirm it and breaker in panel were on?

Well I saw the switch inside when I took off the front panel that switch from "ON" to "OFF" but that didn't seem to do much. I'm not sure if there is a switch other than that...


The breaker has the switch ON for the furnace.

R.G. : Okay on bottom panel of furnace there is a small sight window, can you look in it and see if there are any led lights on, covers must be in place on furnace or door switch will cut power off to furnace.

I will check...


No, there are no LED lights on.

R.G. : Okay sounds like no power to furnace about mid way of furnace could be on either side the electrical wires will enter furnace can you look at those and see where they come from possibly a switch that is off?

Hi there. Thank you very much for your help, but I figured it out. The power switch was hidden but I found it. Thank you for your time.

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