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Heating & Air Conditioning

VERY strange (to me) furnace trouble

15 years ago

The furnace guy is coming today but I'll be astonished if we can duplicate this problem when he arrives.

On four occasions - days apart - for whatever reason the furnace has refused to cycle on when the temp gets down to where it should. We don't notice it until someone of us says 'Hey, it's cold in here.' Wife pushes up the thermostat - no go. Circuit breaker looks good but I switch it off & on anyway - furnace comes on! After the second time I replaced the circuit breaker; I know they can go bad although not often. Yesterday it did it again. This time we flipped the power switch mounted on the furnace itself off & on - furnace came on! To me this means the circuit breaker & power switches are OK. What else can it be? This is a forced hot air gas furnace, and the furnace is the only appliance on the circuit breaker in question. Thanks in advance.

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Comments (6)

iggie
15 years ago
The problem could be caused by almost any thing in the furnace control circuit. I have encountered main gas valves that stick and act in this mannerm turning the circuit breaker on and off gives them a kick and they operate. You need to call a tech he can use a meter and pinpont exact problem when furnace fails to fire. This may sound exoensive, but believe me one can spend a lot of money guessing and haphazardly replacing parts and still not locate the problem. Here is one suggestion the next time furnace does this use a wooden handled screw driver and tap on the main gas valve, if furnace fires you have found the problem. Good luck Iggie
pelican
15 years ago
Iggie, advise like that will put all the service professionals out of business. You nailed in man.

Softball, it sounds like your furnace is locking out for some reason. It could be a high limit switch, pressure switch, flame roll out switch, gas valve, or a number of other problems that are causing this. Reseting the power at the breaker or furnace switch just resets the control board and it starts the process all over until the problems locks it out again. Let us know what the tech does to fix it. You will make his job easier if you do not reset the power or do anything to the furnace when it locks out. Depending on your furnace he may be able to read a code given off of the board. Please don't be poking any wooden handled screwdrivers into it. I am still chuckling over that.
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"Oh its not the t-stat now is it?" I don't know Jeff. ".. sounds like a lockout to me." A lockout needs a hard reset. Once a primary trips - it won't reset simply by cycling the breaker. You have to re-arm the primary manually. "or a number of things that can't be checked over the internet" True, Jeff but diagnosing a lockout over the internet is no more sure than diagnosing a t-stat over the internet. Jeff - no slams here; just diagnosing what we've been told. Cheese- All the stat does is make and break a low-voltage connection. Essentially it's a part of a relay circuit. It opens and closes what is usually a 24v circuit, that's all it does. The stat gets it's working power from the batteries. If the batts are weak; the stat won't reliably close the connection. IOW it isn't always telling the furnace "it's cold, make heat." Jeff wasn't wrong-I just don't believe that a diagnosing a bad t-stat is over your head, 24 volts will not hurt you like 120v or 240v. If you lose power in your display - it's not the 24v from the furnace. It's the stats internal battery power failing - or some other element of the stat failing ie. bad component on the board, or bad contact on the board etc. Are your batteries new? -br
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You're right, Wiley. The repairman demonstrated the lockout by shutting off the gas flow via an internal switch. The limit switch tripped three times and then the circuit board went into lockout. He told me that houses built in the early 60s like mine had duct work that is undersized by today's standards. Putting in a filter that is designed to trap finer particles did indeed restrict the airflow. When you remove the filter while the blower is on you can hear it speed up; replace it an you hear the blower laboring to push air through it. He put in a standard filter and that took care of the blower problem. It's been working fine ever since.
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Thanks for your help! I am very mechanically inclined and have worked with gas and electric many times. I figure, if I can fix a $100k+ lab instrument that runs on hydrogen and is full of delicate electronics, I should be able to handle fixing my furnace. I just don't have a good manual to know all the standards voltages and currents on the boards in the furnace. I've done a lot of googling on this subject, and so far haven't come up with a good answer. My first thought was a corroded flame sensor, since the problem was intermittent. My second thought was a bad HSI. But since my furnace isn't even trying to even heat the HSI, I'm stumped. If the ignitor control module is failing, is it possible to have an intermittent problem like I am seeing? And i know I should just call an HVAC guy out to my house, but I won't be able to afford his time and labor until mid January. My time and labor is free, and I'll probably be able to find the parts cheaper online (assuming I can figure out what is failing).
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Thanks everyone for your comments and advise. I think we will try to seek latex-free condoms. To monablair: I am pretty sure it is not an STD because both my husband and I did were not sexually active before marriage. Is there any STD that is present even without sex? If not, I am really very positive it is not and STD. As for the sores being there between sexual events, as I said, they begin to heal and close but are just broken open again. Preferring a condom even though I am on birth control? I hate the mess to be cleaned up! He doesn't appreciate spilling semen all over the place, either. Plus, we are in college and are still young and wish to take every precaution in the wind towards pregnancy. If a child happens, fine, wonderful. But we'd really rather not at this point in our lives and our marriage. Thank you for the warning concerning latex allergies, neither one of us had any idea. It would have never occured to us that it could compromise his breathing. We just assumed it was a skin allergy and nothing more. =)
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dawger
15 years ago
Softball, Pelican is probably right. Its shutting of due to a problem, as its designed to do. However you probably should've, and maybe you did at least check the condition of the filter the first time you reset it. A clogged filter is an EZ fix.(in most cases for most people)
mr_havac
15 years ago
My GOD iggie those guys are right! What in the world were you thinking about giving advice like that?!!! You are obviously an old timer. Who else would tell someone to use a wooden handled screw driver to tap on the gas valve. Softballs, whatever you do don't listen to this man. This is very poor advice. Use a plastic handled screwdriver instead. :-)
maryland_irisman
15 years ago
mr hvac....wow, I must be out of tune. I've been using a piece of wood for years to push contactors. Where can I get one of those plastic things?
patches_02
15 years ago
Our furnace does exactly the same thing.

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