furnace lazy?


Old 11-15-00, 09:15 AM
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We were having a problem with the old thermostat (or so we thought). It was a lever type that would have to be manually reset sometimes, especially if the temp was shut down to below 60. Recently (within a week ago) the thermostat was having to be reset every time! The furnace would only heat to 60 if it was set at 70. It would shut itself off! Then, we figured out if we set the thermostat at 78, it would stay on all night and heat the house to about 73-very hot! Well, we got a programmable thermostat and thought the problem was solved. But when we came home (the return cycle) the furnace had not started. My husband put the old thermostat back on, and we had the sauna again last night! Thanks for any advice!!!
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Old 11-15-00, 09:24 AM
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If the system works with the old t-stat, then most likely, you may have miswired or misprogrammed, the programmable. Carefully re-wire the new t-stat and put it thru its paces manually. If it works on heat and cool, then most likely, it wasn't programmed correctly. If it works on manual settings, but won't work with the program, you may have gotten a dud (bad out of the box).
Old 11-15-00, 11:56 AM
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Thanks for the advice. I guess I wasn't clear about the problem: the old t-stat only works if we set it about 5-10 degrees above what we want. The new t-stat did seem to work for the first run of the program, but did not kick on after that.
Old 11-15-00, 08:18 PM
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Your posting is totally focused on the thermostat. I doubt the problem is with the thermostat.

What it sounds like is a weak pilot generator. Often times the thermostat is assumed to be the problem when it really could be the furnace or it's pilot generator system.

Would you mind posting a more detailed explaination of the furnace type? Is this a wall furnace? A forced air furnace? A floor furnace?

Please explain what is meant by a level type manual thermostat that has to be reset?

I'll check back here looking for your next posting and hope to help you better then.

Natural Gas Energy Technician and Consultant.

Old 11-16-00, 02:00 PM
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Sorry I'm at work, but I will tell you what kind of furnace tonight. The most frustrating part is that we'll walk in the door, and the house is freezing. The temp is below 60, but the furnace is set at 70. We attempt to "reset" the lever type of thermostat (a lever at the bottom that says what temperature you'd like the temp. to be at) by pushing the lever all the way down to the far left (very cold), then SLOWLY moving the lever to the right until we hear the furnace kick on. I might have to do that 3-4 times before it kicks on. Then, it might do 2-3 cycles and just shut off-still below 60! I might have to reset the thermostat 2-3 times before it will stay on to heat the house up to 70. Thanks again!
Old 11-16-00, 02:05 PM
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Okay, my husband says it is a forced-air gas furnace (by a no-name company). Do you still think it is a weak pilot generator?
Old 11-16-00, 02:33 PM
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Sounds like a heat anticipator type problem or something related to it. A bad gas valve, ignition module, etc. could cause that problem. Gas valves, modules, etc. on the heat circuit pull X amount of amperage. If they are pulling to much it can cause your problem.
Old 11-16-00, 08:23 PM
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Thanks for the updated detailed information.

I think it's a weak pilot generator. Older forced air furnaces used pilot generators to produce current. This millivolt of current is used by the thermostat and the gas valve.

Later model furnaces used the 24 volt systems. Both types of furnaces used similar looking thermostats, like the one you discribed and that you have.

You can tell which type of system you have by looking at the inside cover of the old thermostat. It will be marked for it's type.

One type will be for MILLIVOLT SYSTEMS only.
The other type will state it's for 24/28 DC volt systems only.

Having the incorrect thermostat installed will cause problems. If yours is for millivolt systems only, then your furnace has a pilot generator. Your new thermostat will not work with a pilot generator.

If the old thermostat is for 24/28 volt DC systems, your furnace has a transformer. Your new thermostat will work with this system.

If the old thermostat is a millivolt type, the pilot generator is most likely weak and will need to be replaced. You can also check and attempt to clean the contact points of the old thermostat, if it has them.

Good Luck,
Old 11-18-00, 08:14 PM
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If your gas valve is RED in color it is a millvolt system with a power pile generator.

With it reseting when you turn it down and back up again I would guess a dirty piolot a sensor.

Good Luck
Mr Foster

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