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Old 03-04-2009, 06:22 PM   #1
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Can't control furnace


I have a natural gas furnace.
At first, I could not get the thermostat to turn the heat on.
I bought a new Honeywell digital thermostat.
I am 99% sure it's hooked up correctly as I replaced the 4 wires exactly as they were on the last thermostat.
Now I cannot get the furnace to shut off. The thermostat is programmed at 70 but the furnace keeps heating/blowing.
Ideas?
Is my circuit board screwed up?

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Old 03-04-2009, 06:27 PM   #2
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Can't control furnace


Remove the stat from its base on the wall and see if the furnace goes off.

If it does then look at the stat and see if the fan is selected to the on position. If it is you may have the W and G terminal reversed.

If the selector is on auto then you may have a bad stat.

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Old 03-04-2009, 06:34 PM   #3
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Can't control furnace


Fan in "ON" position, controls the fan properly.
In "AUTO" position, furnace always heats and blows regardless of programed temperature.
What are the chances that a brand new thermo is bad?
Is there another way to eliminate the thermo as the problem?
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Old 03-04-2009, 06:45 PM   #4
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Can't control furnace


Quote:
Originally Posted by angus242 View Post
Fan in "ON" position, controls the fan properly.
In "AUTO" position, furnace always heats and blows regardless of programed temperature.
What are the chances that a brand new thermo is bad?
Is there another way to eliminate the thermo as the problem?

Did you remove the stat to see if the furnace stops?
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Old 03-04-2009, 09:05 PM   #5
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Can't control furnace


When I disconnect the thermo and unhook the 4 wires, the furnace shuts off after a slight delay.
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Old 03-04-2009, 09:32 PM   #6
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Can't control furnace


I would double check the wiring at the furnace control board to the stat.

White wire to W
Red wire to R
Green wire to G
Yellow wire to Y sometimes there isn't a yellow and blue is used

In other word just make sure that W is to W and R is to R and so on

R = Transformer voltage
W= Call for heat
Y = Call for cooling
G = Call for fan (blower)

Yes I have had stats right out of the box that were junk.

Also make sure the stat temp diff is set at 1 or 2 deg. Some stats have a .5 deg and that can cause some issues.
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Old 03-04-2009, 09:53 PM   #7
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Can't control furnace


To me everything looks fine.
Does this mean I don't have to worry about the circuit board and I should try a new thermostat?
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Old 03-04-2009, 10:21 PM   #8
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Can't control furnace


At the thermostat jump the R and W together.

This will cause the furnace to start..let it fire up and start blowing heat.

Then remove the jumper and the furnace should turn off after it cools down.

If this happens..then the control board is ok

Double check the stat set-up settings like;

Gas/electric/Heat pump
Temp differental
F/C

If you followed the set-up instruction and you are 100% right then yes get a different stat
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Old 03-04-2009, 10:54 PM   #9
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Can't control furnace


OK, jumped and furnace did come on and blow hot. Removed jumper and it shut off.
Settings are correct; gas, heating cycle per manual and set to F.

I guess another thermostat is in order. As long as it wasn't the control panel on the furnace!

Thanks so much plumber!!!!!!!
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Old 03-04-2009, 10:58 PM   #10
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Can't control furnace


Sounds good

Glad to be of help

What ever you buy for a stat..Please don't go with a Hunter

Braeburn, Honey Well, Robert Shaw and White Rogers are good brands

Good Luck
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Old 03-05-2009, 09:55 PM   #11
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Can't control furnace


FYI, got a replacement Honeywell thermo and all's good!

Thanks again for the help!

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