funny acting furnace- Tappan model U

Furnace is from 1981, I can't afford a new one so I am trying to get by-
Here is what happens-
The thermostat calls for heat (I hear a click at the thermostat). The intermittent pilot will light (sometimes it will spark 10-15 times before it will ignite). After the pilot lights, the main burners do not come on. Sometimes it is cold in the house (+/- 55 degrees) in the morning, and I assume the pilot has been burning all night without igniting the main burner. This doesn't always happen, but probably it does happen 2 or 3 times a day.
The owner's manual states that after approximately 20 seconds the flame sensor heats-up enough to energize the main gas valve (the gas valve is a White-Rodgers 36C94, type 243).
To fix the problem, I turn off the electricity to the furnace, wait a few minutes and then turn it back on -or- turn the thermostat set point below the room temp., wait until it clicks and then turn it back up.
The pilot then lights and after 20-30 seconds the sensor heats up, I hear a click and then the main burner kicks on and then about 10 seconds later the blower comes on….all as it should
This fix works all the time.
Anyone have an idea about what is going on here??
THANKS!!
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Its *not* a fix because you have to keep doing it.

yup......gotta pretty good idea

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Yup...got a real good idea what is going on.
You are treating a symptom, and not the problem. The problem can be fixed, rather, repaired.
Got a phone? You can get it repaired.
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Not to give you a hard time, but....
I never understood why people will go out and buy a new car every 5 years and pay over $30K for it, but then they will put band-aids on an old, inefficient system that is supposed to provide comfort for them (where they live!) instead of spending a couple thousand dollars to put one in that would not give them any trouble (set it and forget it) and save them money in the long run.
Come on!!! That furnace is 23 years old!!!!!
The only thing that is worse (and I see it all the time) is someone building a half million dollar home and them putting in the cheapest, most inefficient HVAC that money can buy because they "got a deal on it" and then they wonder why they have problems with it all the time.
"My Mercedes is 4 years old and I have never had any problems with it!!!"
David wrote:

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"Dr. Hardcrab" wrote:

I see your point, but please bear in mind that not everyone hanging onto their old furnace is blowing dough on cars, vacations, etc. Some of us having been pouring our money into home repairs as they come up, which has us simply grateful that at least the furnace has kept running.
My current gas furnace (a Montgomery Ward, no less) was installed in 1975. It runs fine, it's given me no trouble, my energy costs compared with my neighbors are very reasonable. Assuming the average lifespan of new furnaces runs about 15-20 years, had I replaced the furnace when I bought the house, by now that new furnace would have been half-way through its useful life.
From my cash-strapped perspective, every year I postpone replacing the furnace is to my financial advantage. Especially since almost one-third of my energy bill is made up of connection fees and other charges completely unrelated to the amount of gas and electricity I actually use. So even when I do eventually upgrade to a new furnace, the energy savings isn't really going to make a substantial difference in my energy costs.
Even so, I have finally decided to to replace it this year, simply because the suspense has been mounting and it's really getting to me. Considering its age, I just _know_ it's gonna die soon, and I'd rather not be caught in an emergency situation. Like I was this past weekend when the water heater (the furnace's contemporary) rusted through... HellT
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Maybe cause this trade is populated by a bunch of crude yoyos that can swing a wrench, but have no idea how to sell or talk to people?
Those few that do, do very well.
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You dont work on new construction much then. Unless the homeowner is acting as his own GC normally, particularly in the large, even the million dollar developments, the GC has an installing company, and they put in whatever in hell they feel like. I cant tell you how many new homes here have Goodman. Most on the market in the 200, to 400K price range. It boggles the mind that a GC would allow it, but they are not looking at quality, they are looking at price, and thats it.
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Your furnace was made by Microsoft. This is normal behavior.
-- Mark Kent, WA
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Does it have the initials of "HP" on the front too? :-)

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kjpro
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Naaah, has the TRS-80 logo

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David wrote:

I can think of a couple of several possible problems. The flame sensor could be going out, or the electronic control could have a problem.
In any case, I strongly suggest you have a professional come out and check it. I suggest this because you could end up paying more for parts than the pro will cost, but mostly because that old furnace may well be a safety hazard due CO. It really needs to be checked professionally. You think you can't afford a new furnace, but if that one is going to kill someone, you can't afford not to replace it.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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Flame sensor or gas valve. That is a pretty old furnace. If you're going to fix I'd suggest inspecting the heat exchanger pretty carefully. An hvac guy can check it with a co detector. A new unit would lower your gas bills about 15% to 30% depending on the efficiency rating.

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Still needs to be checked visually.
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Well, it's obvious from here that something isn't doing its job. Turning it off and on again just resets some kind of safety switch. Makes me wonder what happens if the safety switch fails -- does the gasvalve keep pouring unlit gas into your cellar?
It sounds like you've been quite fortuate that your much exercised safety switch is still working. Time to call a heating guy and have it fixed right.
Oil guys tell jokes now and again about how many times a home owner can press the red reset button on the oil burner -- now we have the chance to tell jokes about a home owner and a natural gas furnace. You're risking your family's safety, here.
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Christopher A. Young
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yeppers, there is n doubt about it I am a total moron hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack hack
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