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HVAC Furnace Questions

Crazy Horse

Crazy Horse

Well-known Member
We have a 20-year old mid-efficiency Lennox furnace. Now and then it decides to quit working, usually for the same flashing
light codes. I have waited them out sometimes and they will kick back in on their own but I usually correct things by
dropping the thermostat setting upstairs and then setting it back to the regular setting. I have the flow chart with all
the possibilities of flashing lights which for the most part is pretty confusing to figure out what is causing it ..... but
that's not my question. Here it is ....

When an HVAC tech comes to the house and all is working well with the furnace, can he still determine the exact issue
without the problem happening when he is there? I would be able to tell him the flashing light sequence during the shut
down. Maybe it's like the auto repair trade where they tell you they can't fix anything until it acts up.
 
If you have the code he should be able to diagnose it.

Sometimes there are teltale signs of what is happening, and different brands have a history of common problems.

A lot depends on the tech. If he's comfortable with the age of the unit and feels he can repair it without sacrificing safety or having to come back because it still has problems, then he will probably attempt a repair. Twenty years is getting up there for the life of the heat exchanger. The last thing a repair service wants is to be responsible for something bad happening after they worked on it.

But there is a chance he's looking to make more money off of a new install. It happens, have to be careful what you believe and agree to.

Do you have the code it was flashing?
 
One of the more common problems is dirt. When was the last time your furnace was serviced? Vacuum the motor out, clean the pilot and burners, air filter, etc. Oil you could also have a weak ignition module or an eroded ignighter probe. Sounds like you really need a full service!!!
 
Yes I do ..... 1) Sometimes it is alternating fast flashes (we have two green led lights) and I can get that back on track by dropping and then resetting the thermostat. The flow chart suggests it could be an electrical ground or voltage issue.

2) Lately after the burners shut down after a heating run, it keeps asking for heat for a while (both lights fast together) and then it slips into a mode where #1 is off and #2 is slow flashing. This code says something to do with a pressure switch issue.

Both will eventually start up on their own, the first issue in about 30 minutes, the second one in about 15 minutes. It is definitely not the heat sensor problem (ignition failure of the burners shortly after firing up) ..... that I would recognize from previous issues and I replaced the sensor a while back and that hasn't happened again.

Just went out for a walk and ran into an HVAC guy in the neighbourhood, he was heading inside a home for a service call. He might be able to drop by and see my furnace, I will keep you posted. Thanks for the reply.
 
Thanks Jeff ..... good idea, it's been a while. Below you'll see that a guy is dropping by hopefully.
 
I used to have that problem every year with an oil furnace in a previous house. I finally found the problem; Cleaning the furnace is a miserable dirty and boring job. For that reason they don't send out an experienced troubleshooter technician. They usually send some loser who is being punished or some inexperienced kid who is on some form of controlled substance. Once I started cleaning the furnace myself every fall I never had another problem.
 
In answer to your question, like Steve said it will depend on the experience of the Technician and what you can tell him about the symptoms and LED operation. It seems like you have a good handle on the latter.

Since you have a Lennox I expect you would have better success with a Lennox dealer. These Technicians work on all brands and it is hard for them to know them all equally as well.

Good Luck.

Paul
 
Most likely, your draft inducer bearings are starting to fail. They can start to seize up a little after the motor has been running for a while. When the draft inducer turns too slowly, the vaccuum level in the heat exchanger drops off causing the pressure switch to open. This causes the furnace to shut down. It may restart when it cools down a little.

It is also possible that the pressure switch is malfunctioning.

I found one the other day where the tube that goes to the pressure switch was plugged up.

A lot of things can cause pressure switch shut downs.
 
If he has access to the code chart he won't have a problem with you knowing what is flashing. Sounds like it is most likely the inducer fan, tube, or switch. All you have to do is jump that switch when it acts up and you'll know for sure when she fires. Gas is pretty simple. Fan, ignitor, gas valve, flame sensor.
 
Thanks OH Boy ..... the inducer motor, is that the little electric motor that is part of a small squirrel cage that provides some extra oomph for the waste exhaus furnace gases to go up the chimney?

While I'm at it, should it be running whenever the furnace is in heating mode?
 
Hi David ..... I copied this from one of my replies earlier to another YT'er ....

1) Sometimes it is alternating fast flashes (we have two green led lights) and I can get that back on track by dropping and then resetting the thermostat. The flow chart suggests it could be an electrical ground or voltage issue.
2) Lately after the burners shut down after a heating run, it keeps asking for heat for a while (both lights fast together) and then it slips into a mode where #1 is off and #2 is slow flashing. This code says something to do with a pressure switch issue.

Both will eventually start up on their own, the first issue in about 30 minutes, the second one in about 15 minutes. It is definitely not the "common" heat sensor problem (ignition failure of the burners shortly after firing up) ..... that I would recognize from previous issues and I replaced the sensor a while back and that hasn't happened again.
 
Yes it is the fan that blows the exhaust out.

Yes it must be running, or the furnace will not fire. If the draft inducer motor stops working while the furnace is running, the furnace will shut itself down.
 
M-Man ..... "Jump the switch"..... exactly what do you mean by that? It would appear to me as if there might be two pressure switches on this, round assemblies with probably a diaphragm of some kind inside ..... both have a rubber hose going into them.
 
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