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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8385
Experience:  Furnace, A/C and heat pump specialist.
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I am installing a honeywell CT87N thermostat in my cabin to

Customer Question

I am installing a honeywell CT87N thermostat in my cabin to regulate my gas fireplace, which heats the cabin. When I touch the screws clamping the red and white wires in the thermostat the fireplace ignites. When I turn the thermostat around and move the dial to a temperature above ambient temp, the fireplace doesn't light. How do I fix this?
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: What filters? How do I check the settings?
JA: Do you plan on doing the work yourself?
Customer: yes. I am doing it now.
JA: Anything else we should know to help you best?
Customer: I don't think so.
Submitted: 1 month ago.
Category: HVAC
Expert:  airheatman replied 1 month ago.

1. Do you have the red to R and white to W

2. Is switch for cycle rate set to left (OFF)?

Customer: replied 1 month ago.
1. yes
2.where is cycle rate?
Expert:  airheatman replied 1 month ago.

Should be on back

Customer: replied 1 month ago.
2. There is nothing referring to cycle rate. However there is a table on the back of the thermostat with off-on switch settings for Steam, Hot water, Gas/oil warm air, and Electric warm air. Is this
Expert:  airheatman replied 1 month ago.

Yes is it set to gas ?

Customer: replied 1 month ago.
the default setting was GAS with the setting for the two switches OFF.
Expert:  airheatman replied 1 month ago.

Do you have a cool,off heat selector and if so is it set to heat?

Customer: replied 1 month ago.
No cool/off heat selector.
Expert:  airheatman replied 1 month ago.

OK if set for gas, fireplace starts when manually jumping tstat but not through thermostat, you may have a millivolt system that requires a millivolt rather than a 24v thermostat

Customer: replied 1 month ago.
Any ideas?
Expert:  airheatman replied 1 month ago.

If the fireplace is millivolt, the 24v stat will not work.You will need a millivolt stat like link I sent.Look on gas valve and see if it says 750 millivolt or 24 volt

Customer: replied 1 month ago.
When I touch the red and white at the wall the fireplace ignites. As I understand it, all the thermostat has to do is make that connection, when the thermometer tells it too. Doesn't all this happen in the thermostat and not at the stove?
Expert:  airheatman replied 1 month ago.

The thermostat is basically just a light switch.However if the fireplace is millivolt rather than low volts, often the thermostat is not capable of sending millivolt signal through

Customer: replied 1 month ago.
I got the wrong thermostat?
Expert:  airheatman replied 1 month ago.

It sounds like fireplace must be millivolt.If so, yes. You will need a millivolt stat rather than a 24v stat.

Customer: replied 1 month ago.
Ok. Thank you.
Expert:  airheatman replied 1 month ago.

HomeDepot has the CT33A which will work

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