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Cannot get a Honeywell 'round' heat only thermostat to

Customer Question
Cannot get a Honeywell...

Cannot get a Honeywell 'round' heat only thermostat to control the furnace. The stat did run this furnace before we shut it down to install a new Propane tank, but since restarting the furnace, I can only get it to run if I remove the stat and jump the R and W wires.

Contractor's Assistant: Thanks. Can you give me any more details about your issue?

I firured the stat was the issue so I changed it. Nothing, same as before. I checked the transformer , it puts out 27 volts. Tried another stat, same thing. In every case, the furnace will run on a jumper, but not on the stat.

Submitted: 2 years ago.Category: HVAC
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Answered in 8 hours by:
1/30/2016
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 2 years ago
BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 23,042
Experience: Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Hello,

just to confirm....you have wires on R and W in the thermostat?

When touched direct together the furnace runs..but does not through thermostat?

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Customer reply replied 2 years ago
Thats right
Customer reply replied 2 years ago
The stat has a three wire terminal for the wires to the transformer, but only the red and white were hooked up when the furnace ran before this problem appeared.
Customer reply replied 2 years ago
The yellow wire from the stat was never hooked up.
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 2 years ago

sorry for the delay.

I cannot say if it was related to shut down...but I can say the thermostat has no provision for being field repaired.

These types of thermostats run less than $40 so the most viable option is to replace.

Whether shut down related or not the connection relay in the thermostat is defective now. The thermostat will need to be replaced.

Billy

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Customer reply replied 2 years ago
Already tried replacing the stat with an exact replacement and with exact same results. This is an older furnace. Rheem model number:RGDA-100C-ER MN3D104 F4290 1877
Customer reply replied 2 years ago
Can there be a problem with the transformer sending too many volts or the correct voltage with wrong cycles per second, or too much amperage?
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 2 years ago

if it works by touching wires together and NOT a new thermostat then the only reason can be less than 24v to thermostat. This would be a transformer issue

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Customer reply replied 2 years ago
I finally got the problem fixed. After trying three (3) thermostats exactly like the original that was installed at the beginning of this odyssey and removing the 'fan control center' and having it tested at a local HVAC shop where it was pronounced "OK", a service tech offered me an old stat of the 'bimetallic spring and mercury tube' type to try. I did and the furnace worked perfectly! It seems that some of the older models will not respond to an electronic type thermostat. Is this something unheard of? After buying three identical stats, dismounting the 'control center' for independent testing, making four or five trips back and forth throughout all this,and asking my questions at this website, on the internet, at HVAC shops, and everyone else I could think of to ask, did it not occur to anyone that the problem might be with the 'type' of stat that was being used? I had mentioned that the furnace was 'old' and given the model number& etc. Would that info. have provided a clue as to what the problem might be?
At the start of my inquiry with you I said that the furnace ran on the originally installed stat before we shut it down to install a regular 500 lb. propane tank, I think I assumed that. It may be that it was never hooked-up to the stat and that the folks just ran it without any thermostat at all. This has been a long ,long process of a job for several people. It is hard to be sure of some things. I have been helping a 'friend' with it, so I was not involved with all the work. The end of it is that I found an older stat with the same shape of the 'spring&tube' construction, installed it and we are good at last.
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