Gas and Oil Home Heating Furnaces - Gas Furnace w/ Intermittant Problems

Friends: Our ThermoPride gas furnace (AGL5-100) was installed in 1986 and the OEM burner was replaced by the mfr in 1994 with a Wayne burner. A relay switch (?) was also replaced by the mfr in 1996. A Honeywell S8600H shutoff has been in-use for many years. The problem occurs intermittantly when the thermostat calls for heat and the exhaust fan starts, etc. The unit is heard to cycle, without producing flame. Shutting-down the system via the kill switch and waiting a few minutes, before switching-on, is the usual remedy. A number of technicians here in Central New Jersey have failed to diagnose the problem, at great expense, and the most recent genius has recommended replacing the entire unit! Any constructive advice would be much appreciated. Thanks!

The average life of a gas furnace is about 15 years. So, don't be too rough on the tech who suggested replacement. A 22 year old unit needs to be checked over carefully for a cracked or rusted out heat exchanger.

The s86 control could likely be the cause of your trouble. They tend to wear out at about 10 years or so. But, everything else must be checked first.

In any case, start budgeting for a new furnace.

What type of ignition system do you have, and have you tried to observe it when it should be trying to ignite?

I can't fathom how these expert repairmen are not able to diagnose your problem. To blindly state about getting a new furnace without saying what they found, sounds ridiculous.

They should be able to tell you if you have a bad heat exchanger, it that what it has, and tell you. Or be able to identify a cause. Not just say you need a new furnace.

I had a furnace guy show up at one of MY rentals once because I could not get home in time, and he suggested the heat exchanger was badly rusted and needed a new furnace. When I got home, I took a careful look and found no such thing, and the metal was extremetly thick, no cracks, just a surface rust layer (like corten steel gets - if that). Needed a new gas valve. I went to a used and new parts guy I deal with, got a used valve for $25 and saved the $1500 he said it cost for the new furnace. Got 2 more years of trouble free service out of the furnace til we finally upgraded to higher efficiency one offered to us as part of the rental upgrade program that we opted for.

A landlord I deal with was told by housing authority he needs new furnace - based on - exterior looks. Landlord still has had trouble free service from this old furnace for about 12 more years since being told that! In fact, I have not had to go there and work on it this winter so far, and it has been almost 20 below at times. But I HAVE had to work on various newer high efficiency ones.

There are many furnaces in rentals from the late 80's to early 90's vintage (high efficiency types) and all of them seem perfectly fine.

But I highly recommend for everyone to invest in one of the newer gas/CO detectors. And if a person has a family, and values your own life and theirs, I'd get like 3 of them placed in various areas of the house.

A Honeywell S8600H shutoff has been in-use for many years.

The s86 is known as a "spark box". After 10 years they are prone to failure. Cracked solder joints or bad relays on the circuit board are the usual cause of failure.

The s86 is known as a "spark box". After 10 years they are prone to failure. Cracked solder joints or bad relays on the circuit board are the usual cause of failure.

Jim: Many thanks for your thoughtful responses! I am very much the amateur in this area and very grateful for your advice. Stay well. Jim McGarry

Ecman51: Thanks very much for your kind response and concern for our safety! Like you, I believe in safety and have previously installed CO detectors in the immediate area of every combustion source. I will get the advanced type detectors, however, without delay. On the subject of the furnace itself, I am determined to get that puppy working correctly and know a lot more now, thanks to you! Stay well. Jim McGarry

What type of ignition system do you have, and have you tried to observe it when it should be trying to ignite?

I can't fathom how these expert repairmen are not able to diagnose your problem. To blindly state about getting a new furnace without saying what they found, sounds ridiculous.

They should be able to tell you if you have a bad heat exchanger, it that what it has, and tell you. Or be able to identify a cause. Not just say you need a new furnace.

I had a furnace guy show up at one of MY rentals once because I could not get home in time, and he suggested the heat exchanger was badly rusted and needed a new furnace. When I got home, I took a careful look and found no such thing, and the metal was extremetly thick, no cracks, just a surface rust layer (like corten steel gets - if that). Needed a new gas valve. I went to a used and new parts guy I deal with, got a used valve for $25 and saved the $1500 he said it cost for the new furnace. Got 2 more years of trouble free service out of the furnace til we finally upgraded to higher efficiency one offered to us as part of the rental upgrade program that we opted for.

A landlord I deal with was told by housing authority he needs new furnace - based on - exterior looks. Landlord still has had trouble free service from this old furnace for about 12 more years since being told that! In fact, I have not had to go there and work on it this winter so far, and it has been almost 20 below at times. But I HAVE had to work on various newer high efficiency ones.

There are many furnaces in rentals from the late 80's to early 90's vintage (high efficiency types) and all of them seem perfectly fine.

But I highly recommend for everyone to invest in one of the newer gas/CO detectors. And if a person has a family, and values your own life and theirs, I'd get like 3 of them placed in various areas of the house.

The s86 is known as a "spark box". After 10 years they are prone to failure. Cracked solder joints or bad relays on the circuit board are the usual cause of failure.


Actually, the S8600 Honeywell ignition control box is the single most reliable way of igniting a gas furnace I have ever encountered. The one I installed in my furnace in 1985 is still going strong, even after being drowned in a flood, following being dryed out in a warm oven for a couple of hours.

It's rare that even old ones need to be replaced, in my experience.

The problem occurs intermittantly when the thermostat calls for heat and the exhaust fan starts, etc. The unit is heard to cycle, without producing flame. Shutting-down the system via the kill switch and waiting a few minutes, before switching-on, is the usual remedy. A number of technicians here in Central New Jersey have failed to diagnose the problem, at great expense, and the most recent genius has recommended replacing the entire unit! Any constructive advice would be much appreciated. Thanks!


Unfortunately, intermittent problems are the bain of repairmen. A competent repairman who can observe and test a problem can usually diagose the problem, but if it isn't there to be observed, or disappears when the equipment is inspected or touched, it can be very difficult ---one can be left to guessing and supposing what the problem might be, which isn't a reliable troubleshooting method.

Usually, such problems progress from being intermittent to being chronic, then permanent, at which point they can be pinpointed pretty easily. Sorry yours appears to be the exception by remaining intermittent over a lengthy period of time.