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Any Furnace Experts Out There?

K

Kozman

Tug Review Crew
TUG Member
Joined
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Messages
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Location
Farmington Hills, Michigan
Recently I've been having trouble with my furnace not coming on when the thermostat is calling for heat. It will work fine all day and then upon waking up the temp will be at 58 when it should be 66. If I turn the heat off and then back on it will fire up and heat fine. My first guess was to buy a new thermostat, but that didn't fix the problem.

Any heating and cooling experts out there who can advise me on what might be the problem. My second thought is that there is a sticky relay or perhaps a bad ignitor (it's a high efficiency pilotless furnace). I'm thinking of opening up the unit and tapping on any relay looking thing I can find to see if that will bring it to life. I'm quite handy mechanically, so would like to avoid a furnace repairman if possible. But, I definitely have to fix it reliably before my next TS trip.
 
What does the trouble-shooting section of your owner's manual say? Does your furnace have a trouble shooting indicator light? Ours blinks a code that we can then look up in the book. I still ended up calling a repairman who cleaned out the thing and replaced a sensor.
 
I never thought of looking in the owner's manual where ever it is. But, that sounds like an idea. Even if there is a schematic inside the panel that would be helpful. I have out of town guests so I haven't really gotten serious about the repair.
 
Had a similar problem just last week. Fortunately we have a maintenance contract with the Gas co. ( well worth the $15 per month for air, heat and hot water repairs)

The first time they came out, the tech cleaned the sensor and replaced the ignitor. Worked for 2 days and started acting up again. The gas would ignite, but, not stay on.

The second tech, after checking everything, replaced the circuit board. He said that he noticed that one of the indicator lights on the board was flickering, and it should be steady on when calling for heat.

Has been working fine so far.

Good luck
 
Bad Actuator ?

When the thermostat calls for heat, the high-efficiency gas furnaces starts by turning on the "actuator" blower that gets the air moving through the intake tube that brings cold air from outside into the firebox (so you won't be burning inside air that's already been warmed).

Sometimes the actuator motor conks out or gets balky. If that's it, then replacement is called for -- not an impossible D-I-Y job, but 1st you've got to get the exact replacement part, not some generic 1-size-fits-all item.

One time the high-efficiency gas furnace at our son's house conked out. He & our daughter-in-law were both at work when the repair technician showed up, so we went over to meet the furnace fixer. He found that the actuator motor worked OK, but that there was still too little airflow to allow the gas valve to open so that the ignitor could light up the firebox.

The trouble turned out to be a blockage in the intake tube. A bird had flown in, had got stuck, had expired in there, & had completely dried up. The desiccated remains restricted the flow to the point that the ignition cycle could not start. The repair guy removed the dead bird, reattached the air intake line, rechecked everything, turned the system on & -- FOOF ! -- the fire started & the house heated up OK.

-- Alan Cole, McLean (Fairfax County), Virginia, USA.​
 
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AwayWeGo said:
When the thermostat calls for heat, a high-efficiency gas furnaces starts by turning on the "actuator" blower that gets the air moving through the intake tube that brings cold air from outside into the firebox (so you won't be burning inside air that's already been warmed)....
Click to expand...

That's not the case with many furnace designs. Unless you have a dedicated inlet air duct which day lights outside the home, the inlet air is recirculated from return air ducts throughout the home. That way you DON'T have to consume extra energy just to heat the outside air. It's one of the "green energy" design features to save heating costs.
 
How It Works -- But I'm No Expert.

Kal said:
That's not the case with many furnace designs. Unless you have a dedicated inlet air duct which day lights outside the home, the inlet air is recirculated from return air ducts throughout the home. That way you DON'T have to consume extra energy just to heat the outside air. It's one of the "green energy" design features to save heating costs.
Click to expand...
You save on heating costs by burning cold outside air brought in through those dedicated tubes.

Those tubes are a principal feature of high-energy gas furnaces -- cold outside air in, warmish exhaust air out (after just about all the heat has been wrung out of it).

Burning cold air instead of warm air is a non-factor in saving energy. Gas ignites so readily that preheating of the air (or the gas) is unnecessary.

When you burn inside air, that air combines with the gas via combustion & goes right up the flue -- i.e., it's gone. To replace it, cold outside air is drawn in through the cracks in your insulation around doors & windows & it cools down your house, requiring more heating -- i.e., burning more gas -- to get the temperature up again.

You could look it up.

-- Alan Cole, McLean (Fairfax County), Virginia, USA.​

 
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It takes more energy (BTU/scf) to combust humid outside air than dry inside air. That's a key point with >90% efficiency furnaces as the only way to get that efficiency is to operate at the moisture condensation level. Furnaces with <90% efficiency don't operate at that level.

Air tight homes???? Not.
 
I believe a call to a good HAVAC expert in your area is warranted at this point in time.

frenchieinme :hi:
 
Kal said:
It takes more energy (BTU/scf) to combust humid outside air than dry inside air. That's a key point with >90% efficiency furnaces as the only way to get that efficiency is to operate at the moisture condensation level. Furnaces with <90% efficiency don't operate at that level.
Air tight homes???? Not.
Click to expand...

Both you and Awaywego are correct but I belive each of you are talking about different aspects of the furnace operation.
The combustion chamber has its own small fan that pulls cold outside air into the combustion chamber and up the flue along with the burnt gas fumes. My furnace is in a unheated garage and pulls its cold air from there. Other furnances inside the home will usually have duct work to supply unheated outside air for the combustion chamber use only.
The heatexchanger fan circulates the warmer heated air inside the house. pulling air from the cold air return thru the heat exchanger and out thru the ducts and air registers inside the home.
The combustion chamber and heatexchanger are two seperate airflow paths.
you don't want combustion chamber gases inside the home.
 
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Any Batteries?

Check thermostat. Change out if there are any.
 
http://www.hvac-talk.com/vbb/forumdisplay.php?f=1

Don't know if you'll like their bedside manner but there's a lot of knowledgeable contractors over there...

I could offer up a few suggestions if knowing the make and model. My instinct is a board problem (electronic controls within the unit).
 
The furnace is an Amana 96% and about 10 years old. Uses natural gas for fuel. As of this morning, it's been running perfectly for almost two days. This makes the situation even more difficult to troubleshoot. Maybe the bird became dislodged from the air intake?? Or, the gremlins left for their timeshare. :crash:
 
Glad to hear it's working OK right now. Bad time for needing a heater serviceperson...

Is this anything like what you have?

http://vhphvac.com/webapp/GetPage?pid=373

We use unitized HVAC units out west but my mom still has a split system with a stacked evaporator on top of a furnace similar to that pictured above. Is your unit a stand-alone furnace or does it have air handling for air conditioning as well?

When you "turn the heat off", do you mean you did it at the thermostat (turning the switch to "off") or did you cut power entirely to the unit, at the breaker?

We have a Lennox unit of vintage similar to yours on my wife's house and it has a two-stage air-handling system with self-diagnostics, kinda like most modern cars. When something goes wrong, the computer stores codes that a tech can read. It also has indicator lights that flash when there are control or sensor problems. They're all contained within the unit on its control board.

Like someone upthread mentioned, that's really HVAC tech territory, but you might find clues and some possible remedies on the forum I linked.

One last thing.....can you verify location, condition and continuity of the control wire system for the unit? Our phones sometimes go wonky out here after storms (moisture affecting the underground cables) and similar gremlins can affect low-voltage HVAC control cabling, depending on the environment and how the cable was installed and maintained. Voltage transients in the power grid can also affect the electronics of the unit. Any big storms or unusual weather of late? Any work done on the house? Sometimes the problem is in the little things :)

Good luck!

Pat
 
camachinist said:
Glad to hear it's working OK right now. Bad time for needing a heater serviceperson...

Is this anything like what you have?

http://vhphvac.com/webapp/GetPage?pid=373

We use unitized HVAC units out west but my mom still has a split system with a stacked evaporator on top of a furnace similar to that pictured above. Is your unit a stand-alone furnace or does it have air handling for air conditioning as well?

When you "turn the heat off", do you mean you did it at the thermostat (turning the switch to "off") or did you cut power entirely to the unit, at the breaker?

We have a Lennox unit of vintage similar to yours on my wife's house and it has a two-stage air-handling system with self-diagnostics, kinda like most modern cars. When something goes wrong, the computer stores codes that a tech can read. It also has indicator lights that flash when there are control or sensor problems. They're all contained within the unit on its control board.

Like someone upthread mentioned, that's really HVAC tech territory, but you might find clues and some possible remedies on the forum I linked.

One last thing.....can you verify location, condition and continuity of the control wire system for the unit? Our phones sometimes go wonky out here after storms (moisture affecting the underground cables) and similar gremlins can affect low-voltage HVAC control cabling, depending on the environment and how the cable was installed and maintained. Voltage transients in the power grid can also affect the electronics of the unit. Any big storms or unusual weather of late? Any work done on the house? Sometimes the problem is in the little things :)

Good luck!

Pat
Click to expand...

Thanks for the help Pat and all. I have a model GUC-X or GUX-X or GUD-X. The manual covers all three models. 115,000 BTU 95% efficient.

Even though it is working fine now, I'm probably going to have it checked out by a pro (it's against my basic instincts, BUT!). I can't be going to FL for extended periods of time and depend on it working when it's been faulty in the past. I hate to try and fix something that ain't broke.
 
John, it's 78, and clear in Lehigh NOW. Hope you get your furnace fixed before you come down....
 
Late model furnaces generally require service manuals and diagnostic tools, like code readers and/or laptops with service software on them. I'd never consider servicing my wife's Lennox, except for simple mainenance, but have no qualms working on our 40 y/o Carrier or my mom's 50 y/o General Electric. They're simple and mechanical (relays and switches).

Good luck and stay warm!
 
JoAnn said:
John, it's 78, and clear in Lehigh NOW. Hope you get your furnace fixed before you come down....
Click to expand...

JoAnn, Now you make me want to come down there right now. It's going to be mid 50's here tomorrow so maybe all this white junk will melt. Maybe that's why the furnace is starting to work. It figures it isn't needed as much as when it was 5 last week. Will catch you late Jan.
 
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