the furnace hot surface ignitor will not glow | If a furnace has a bad ignitor, loose wire connections, open limit switch, open rollout switch, open pressure switch or bad control board. This is what you might see in the furnace sequence of operation: Thermostat calls for heat when you turn up the thermostat | You should fist check to make sure you are getting 24 to 28 volts AC between the W (white) and C (com) terminals on your control board. |
| | Make sure furnace blower door safety switch is pressed in when testing. If your control board has a fuse on it make sure the low voltage fuse is not blown. You might have to temporarily tape the blower door safety switch closed for temporary testing. If the fuse is blown on the control board nothing will happen. If the fuse is blown you might have a short in the low voltage thermostat wires. Check to make sure wires are not pinched anywhere |
| Draft inducer motor starts. | If draft inducer does not start then you either have a thermostat problem, thermostat wiring problem, loose wire connection, transformer problem, bad draft inducer relay on the control board or a draft inducer problem. Please make sure you can spin the draft inducer wheel freely. Sometimes if the draft inducer sits for a long time (like over summer) without operating the draft inducer wheel can become tight |
| Pressure switch attached by a small plastic or rubber tube to the draft inducer senses the negative pressure produced by the draft inducer and closes | You should have 24 volts to ground across both terminals on the pressure switch. If pressure switch is not closed with draft inducer running check for a stopped up vent or a stopped up condensate drain line if you have a condensing furnace |
| Limit Switch and rollout switch/switches should all be closed. | Press in on the reset button in the center of each rollout switch to make sure each rollout has been reset. You should have 24 to 28 volts from each terminal to ground. On most furnaces the ignitor will not glow unless all the safety controls (limit, rollout switch/switches, pressure switch) are closed. If a limit or rollout switch is open then you might have an over heating problem and a possible dangerous condition. If the Limit or rollout continues to trip I would strongly recommend calling an HVAC service company to check your furnace out |
| Draft inducer runs for 30 seconds to a minute before you hear a gas hissing sound | If you hear a hissing gas sound with no gas ignition then more than likely either the ignitor is broken or the relay on the control board that sends power to the ignitor is broken. If 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 will shut down, and try ignition again. Most of the time after three tries the furnace will and go into a lock out condition until you turn your power switch back off and on again |
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: Thermostat calls for heat | |
| Draft inducer motor starts | |
| Pressure switch attached by a small plastic or rubber tube senses the negative pressure produced by the draft inducer and closes | |
| 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 |
My furnace’s ignitor does not glow? | This could be a pressure switch, limit, roll out switch, or furnace control board problem | f your vent piping is open, the hole in your draft inducer is open (not clogged with debris or water) and your pressure switch is working properly, then pressure switch will close the connection between two wires and send a signal to the control board |
Draft inducer will not start, ignitor will not glow or gas valve will not open | | Any combination of the above problem or problems could be caused by a bad furnace control board. I always troubleshoot and test the least expensive parts first, such as the pressure switch, limit switch and rollout switches to make sure they are all closed and operating correctly before I go to the control board. First, and most important things to remember is turn your electrical power off to the furnace. Most control boards are located in the blower compartment. Many control boards have a fuse located on them to protect the board from getting burned up if you have a short to ground. The fuse is usually a 3 to 5 amp fuse similar to the fuses that you might find in a car’s fuse box. |
Electric heat will not come on or fan will not come on | | First and most important, Please make sure your electrical power is turned off before trying to repair or inspect any type of electrical appliance. |
| | Inspect the inside of the air handler or electric furnace for burnt wires |
| | Check your breakers or fuses inside the air handler. Again, make sure your power is off. |
| | If you still are not getting electric heat then you should test your sequencers to make sure they are working |