PROBLEM WITH MY HOME HEATING FURNACE

[Hi Ho Silver]

I would appreciate any thoughts about this problem:

Thermostat calls for heat. The little purge air blower comes on. The "glow plug" comes on. Gas does not come on. After a minute or so, the glow plug goes out. This situation may continue for some hours, with the purge air blower on and the glow plug coming on from time to time, but no heat. There is a green diagnostic light on the gas control; it is flashing bright/dim (which the manual says it does in normal operation).

I usually go through these kinds of steps to get it to respond properly:

-there is an off-on switch on the gas control body; I cycle this off and on once or twice.

-there is a wall switch for the whole furnace; I cycle this off and on once or twice.

-I switch off and on the thermostat on the wall.

After some combination of the above steps, the furnace will properly go through its proper sequence: purge air blower, then glow plug, then the small pilot burner, then the main burners, then the main blower. It will continue to cycle properly for several cycles, perhaps days. Then it will flunk out again. Problem has occurred twice during this winter season.

I have also noticed a slight variation where the purge air blower comes on for several minutes and then stops without ignition occurring, with that sequence repeating several times (maybe 4-5 times) after which the gas ignites.

Salient facts: natural gas furnace; 80,000 btu/hr Honeywell thermostat and gas control Houston, TX about 7 years old; as far as I know, no maintenance has ever been done furnace is in a closet in my one story home there is no smell of gas during the problem A label on the unit "installer's instruction manual" shows: Consolidated Industries Lafayette, IN Mod # MBA 080 NH4R Serial # 990917039

Thanks.

[Pop]

I can't help you directly, but ... if the furnace hasn't been serviced in years, it definitely needs service. The problem could be as simple as smudged stuff on the detectors or bad arc gaps, both of which normal PM service would catch. It could even be a combo of simple things due to the lack of service.

IMO, it's time for a service call. Yearly is usually plenty often enough, but some suggest more often, depending on the climate in the area.

HTH,

Pop

[stevie]

I'm afraid i don't have a really good answer for you.

several years ago, my gas range had a somewhat similar problem. the igniter (??) would glow, but the oven would not come on because the gas would never come on. the repairman said the igniter was bad (not pulling enough amps i think). after replacement of the igniter, it worked fine.

however, the same symptoms occurred about 2 years later. this time, i replaced the part myself. the stove has been OK since then.

Thermostat calls for heat. The little purge air blower comes on. The "glow plug" comes on. Gas does not come on. After a minute or so, the glow plug goes out. This situation may continue for some hours, with the purge air blower on and the glow plug coming on from time to time, but no heat. There is a green diagnostic light on the gas control; it is flashing bright/dim (which the manual says it does in normal operation).

I usually go through these kinds of steps to get it to respond properly:

-there is an off-on switch on the gas control body; I cycle this off and on once or twice.

-there is a wall switch for the whole furnace; I cycle this off and on once or twice.

-I switch off and on the thermostat on the wall.

After some combination of the above steps, the furnace will properly go through its proper sequence: purge air blower, then glow plug, then the small pilot burner, then the main burners, then the main blower. It will continue to cycle properly for several cycles, perhaps days. Then it will flunk out again. Problem has occurred twice during this winter season.

I have also noticed a slight variation where the purge air blower comes on for several minutes and then stops without ignition occurring, with that sequence repeating several times (maybe 4-5 times) after which the gas ignites.

Salient facts: natural gas furnace; 80,000 btu/hr Honeywell thermostat and gas control Houston, TX about 7 years old; as far as I know, no maintenance has ever been done furnace is in a closet in my one story home there is no smell of gas during the problem A label on the unit "installer's instruction manual" shows: Consolidated Industries Lafayette, IN Mod # MBA 080 NH4R Serial # 990917039

Thanks.

[JJ]

I recently had a similar problem with my gas furnace (a "gas pack" which sits outdoors). Turned out to be a faulty pressure reduction valve in the gas line between the meter and the furnace. Have had no problems since it was replaced. I don't know if this relates to your situation but thought I would pass it along. Good Luck!

[Mr.E]

Check the exterior vent discharge for obstruction. May be that low air flow is not allowing safety switch to close reliably.

[Hi Ho Silver]

Later update: I have now noticed that occasionally one of the four gas burners (the one nearest the gas valve) fails to ignite from time to time. I did have a service man come to the house yesterday; he thinks the problem is in the furnace gas control valve. He rapped on the supply pipe a couple of times after which the fourth burner would relight. Overnight, I found that either there were only three of four burners lighting, or the total amount of four flames was less than normal. I rapped on the pipe again; the burners all went out, then relit when the cycle called for heat and for now they have heated the house ok. I plan to get another service call. Thanks

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[Brian]

If you smell gas, contact the hvac/gas company directly

Else

Click reset door switch switch

Disconnect Thermostat, and connect R & W. This will create call for heat.

Check 24v at gas valve. If you have power, gas valve is stuck.

....

[Bubba]

Brian, You dont have a clue. Stay away from what you dont know. Bubba