Re: lennox 80 ugh furnace turns on, ignites gas and shuts...
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electronic ignition or pilot type? assuming electronic ignition, check the airflow sensor for dirt in the peto tube, or a defective sensor, if you hear the high voltage click but have a failed ignition chec that the pilot is being lit, and that the thermopile/infrared sensor is good. one of those is your problem.
Usually when your flame sensor gets dirty, the igniter and burner come on for approx.15 seconds, then shuts down. After 3 tries it will lock the furnace out. You have to shut the power off to the furnace then turn it back on to reset it. You need to turn all the power off to the furnace and remove the flame sensor, clean it with some very fine steel wool and put it back in. Be careful not to handle the Sensor (metal) part with your fingers. Turn the power on and set your thermostat so that it will call for Heat. That should fix, it if not you may need a new flame sensor.
Turn power off & on again. Watch to see if it cycles...it could be the hot surface igniter if you don't see it turn bright orange. If it goes straight to blowing cold air, then normally it is a limit switch open- mostly manual reset - thermal disc-located around flame rollout.
Nov 17, 2012 - Uploaded by grayfurnaceman
This furnace should light its pilot with a spark then the pilot proves its on ... Troubleshoot an ignition problem on a Lennox gasfurnace .... Pilot and no inducer but is the same model as that great video! ... You probably have dirty burners. ... How do you know spark module is not sending 24 volts to mv and pv ...
I've got an easy way for you to check, and then we can help you from there. First pop open both lids to your furnace (this may require a screwdriver). Turn up your thermostat, push the safety interlock button in if it has one (it's a button that turns off the power when the doors are removed), and watch.
On most modern furnaces (past 20-25 years) you'll hear/see: 1. Inducer fan 2. orange glow (ignitor) 3. Gas valve opening and ignition (flames) 4. Main Fan.
that's normal heater operation. The most common issue here is a burned out ignitor, in which case you wouldn't see the orange glow but the sequence would attempt to continue anyway (the gas valve will open and hiss gas, but it won't lite, then it'll give up and try again a few minutes later).
On older furnaces there's a pilot light to start with, the click of the gas valve and boom... ignition.
On new furnaces it's Inducer fan gas valve opening spark - ignition Main fan.
and there are some oddballs in between, particularly the Lennox Pulse. If that's your furnace just back away slowly and call a professional... some guys won't even touch those, so be sure to mention what it is... if you call a pro.
So go ahead and watch it run, then tell me/us what you see.
It sounds like you're describing one of two things. The hot surface ignitor in a gas-fired furnace, or the resistive heat strips in an electric furnace.
The hot surface ignitor in a gas-fired furnace lights the burners. This ignitor in modern furnaces serves the same purpose as the standing pilot flame did in older furnaces. It provides the required heat to ignite the gas at the burners. Without an ignition source, a gas-fired furnace cannot provide heat. When the ignitor is activated it will glow bright orange or yellow.
The resistive heat strips in an electric furnace actually provide the heat to a home or building. When the furnace turns on, the heat strips are activated and usually glow orange when they reach peak temperature. In almost all cases, the heat strips are not easily seen or accessed without removing covers or panels inside the furnace.
Problem: Your furnace will not ignite the gas to produce heat
for your home. When a furnace has a bad igniter what I see most of the time is
the following sequence of operation:
1. Thermostat calls for
heat. 2. Draft inducer motor starts. 3. Pressure switch attached by a
small plastic or rubber tube senses the negative pressure produced by the draft
inducer and closes. 4. Draft inducer runs for 30 seconds to a minute before
you hear a gas hissing sound. The ignitor did not glow, the flame sensor (a
small metal probe about 1/8" in diameter, with a white porcelain base) does not
sense the flame, so after 8 to 10 seconds the hissing sounds stops with no
ignition of gas to heat your home. Your furnace shuts down and goes into a lock
out condition until you turn your power switch back off and on again. Then the
sequence starts all over again with no ignition of the gas. Solution: You
probably need to purchase and install a new igniter. I would suggest that you
inspect your igniter closely for cracks. Make sure you do not touch the igniter
with your bare hands. If you do not visually see a crack, then you could have a
furnace control board problem or a limit, roll-out switch problem. The furnace's
control board might not be supplying the voltage to the ignitor. If your
furnace lights and the gas stays on for 8 to 10 seconds, then shuts right back
off, then you need to clean your flame sensor with light sand paper or steel
wool. You might need a new flame sensor, but most of the time they can be
cleaned an will work well after cleaning.
Sounds like a dirty flame sensor.
Also 9 degrees is a large swing to recover. Most specialist will advise no more than a 5 degree set back, otherwise recovery time eliminates any savings you may achieve.