Thread: furnace stopped working

Problem: Your furnace will not ignite the gas to produce heat for your home. When a furnace has a bad ignitor 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 ignitor. I would suggest that you inspect your ignitor closely for cracks. Make sure you do not touch the ignitor with your bare hands. If you do not visually see a crack, then you could have a furnace control board problem or a limit, rollout 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. Please see the pictures below to help you identify a flame sensor.

Below are pictures to help you identify what a flame sensor and ignitor look like. On the left is a picture of three different types of flame sensors. On the right is a picture of a hot surface ignitor. Make sure you do not touch the gray glass part of the ignitor. If you do it will shorten the ignitors life.

Problem: My furnace's ignitor does not glow? This could be a pressure switch, limit, roll out switch, or furnace control board problem.

I see this problem many times during the heating season . When your thermostat calls for heat the draft inducer (please see pictures below) should start which creates a draft in your vent pipe. If your vent piping is open and your pressure switch is working properly the pressure switch will close the connection between two wires and send a signal to the control board saying, "Yes it is OK to continue with the ignition process."

Also, all of your limit controls and other safety devices must be closed (a closed circuit between the two connections) to allow the furnace ignitor to glow and start the ignition process. If there is a break down in the pressure switch or other limit safety controls the furnace, for your safety, will not proceed with the ignition sequence. The computer chip inside the board says, Wooooh, something is wrong here! Most furnaces will try this sequence for a total of three times then lock out. On most furnaces the only way to get them out of lock out mode is to turn the switch (looks like a light switch) on the side of the furnace to off and then back on again.

fliped the switch on and off several times same thing.
the inducer does not come on . the furnace will click when I move thermostad to make it come on , then the furnace will only hum.
checked the inducer by cutting exstinsion cord and plugging in the plug end ,
fan will come on then. the glow plug does not light at all.
was told by someone if inducer wont come on then glow plug will not work,
if that is true then has to be something else between the inducer and the curcuit I guess. The brain box with all the indicater lights says if there is a problem with the box a light will come on, there is no lights.
there are some condenser like with wires plugged in them, but would not no if any of them could be the problem not knowing what is what, if I posted a pic could you help? thankyou