Troubleshooting new digital thermostat: no heat!

[jhedger]

Hi,

Have a 1926 San Francisco home with a Carrier WeatherMaker 8000 gas furnace heating system installed. We wanted to update the old mercury thermostat with a digital programable one, mostly to avoid having one person wake up early, turn on the heat, and come back to bed every morning.

We purchased a Honeywell RTH7400D unit (5+1+1). Now I'm feeling like an idiot because I can't get the damn thing to turn our heat on!

The old set was very simple: two wires connected. One to "R" and the other to "4". The manual says to remove the jumper between RC/R and install the two wires with "R" = "RC" and "4" = "R". Done. Doesn't work. Hook the old up and it works fine. Bump the wires together and it works fine.

Tried different settings and adjustments to no avail. I hear the internal 'click' when the Honeywell turns "on". But it doesn't start the heat unit.

Does anyone have any ideas??? I'm feeling pretty incompetent as my wife's girlfriend took her new thermostat and two wires and was hooked up and running within 30 minutes.

There are two wires running to the mercury from the "R" spot on the old thermostat if that makes any difference.....

-JC-

[Jerry G.]

I am not too familiar with your exact model. Some of these require a compatible system by where the thermostat is working an electronic device, rather than a hard contact relay, which may be required or your particular heating system. You would be best to contact Honeywell, and also the manufacture of your furnace to know about any possible details for compatibility with their thermostat, and your model of furnace.

The only other thing I can see, is that the thermostat you have may be defective.

[Oscar_Lives]

Try asking these folks:

Honeywell International Inc.

101 Columbia Road Morristown, NJ 07962 Phone: [phone] Fax: [phone]

[Travis Jordan]

Old R - transformer power - connect to R on RTH7400 Old 4 - call for heat - connect to W on RTH7400

Don't ask why Honeywell shows it differently in their owner's manual. For your application, their instructions are incorrect.

Enjoy.

[jhedger]

We are estatic that we now have programable heat! Thank you so much, Travis! I'd really love to know *why* Honeywell shows it differently but I won't ask per your instructions. :-)

[Travis Jordan]

Glad that everything is working for you. The RTH7400 is really a very good thermostat, easy to use and quite accurate as to temperature control. Just don't forget to change the batteries once a year or so.