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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.
Several steps here to check...
turn power off unit and back on
set thermostat to heat
watch for pilot to ignite..igniter should glow orange or cherry red or spark if its a spark type ignitor
Did you see a pilot light ignite?
If not you probably have a bad igniter.
If pilot lit....in a little bit you hear a click of the gas valve opening..then the main burners will ignite
If you see the pilot and the main burner lights but goes out in a few minutes or immediately you may have an issue of the "high limit" switch tripping.
Is the blower fan turning that blows air out of your vents?
are all your vents open in your house? too many times i see homes with almost all vents shut.
if its between 1992-1999 it would be caused by the either the pilot not staying alight, or a faulty gas valve not opening,
These models start the fan on a time delay not tempreture so you will only get cold air circulating and when the thermostat is off the fan will stop.
(All models) if the fan is running regardless of the thermostat position an over heat sensor is faulty.
first have the heat exchanger inspected for a hole or crack, if there is an oval to round adpt. on top of unit or an elbow in vent this can cause the heat exchanger to split open and also cause what you are talking about.
The pilot light has to be lit before gas valve will operate. That's a safety feature so the valve won't open and fill the garage with gas and possibly cause an explosion or fire. If you have a standing pilot and can't get pilot to stay lit, it's usually the thermocouple and it will need to be replaced. Once the pilot is lit, the gas valve comes on and heats the combustion chamber up to approx. 100° to 125° a thermostat controlled fan switch will close and bring the blower on.
that s correct the control is done by the thermostat stop the heating up to your set point and restart if the medium temp is under the set point
if this sequence fail means
- no power to the control element or is defective