Understanding the basic operation of your oven is important when you try to analyze what could be going wrong with it when it stops generating heat. You should know before you start that there are three basic ignition systems used on most gas ranges—the pilot ignition, the glow igniter, and the spark electrode ignition.
This analysis will refer mostly to gas stoves equipped with glow igniter systems, with the pilot ignition and spark ignition system described later, but omitting the “constant pilot electronic ignition” system, which hasn’t been used since the late 1970s.
Before attempting any work on a gas stove, do realize that you’ll be working around gas and sometimes live circuits, so you should have a very comfortable understanding of both specialties—if not, you should call a specialized technician to do your repairs and avoid accidents that could, in this case, be very serious.
Oven Glow Igniter Systems
This is the most commonly used system and is classified as electronic ignition.
In this igniter’s electrical circuit, the 120 volts supply (hotline) is fed to one side of the oven control button (analog) or the electronic control board to be then connected to one terminal of the glow igniter with the other terminal connected in series with one terminal of the oven gate valve, with its other terminal returning to the neutral side of the power source.
If the oven is equipped with the more common glow igniter, turning on the heat in the oven means activating the analog control button or the electronic control board touch-pad which in turn switches on a specially designed heater (the igniter) to a 120 volts power source and heats it up.
A 120 volts igniter will glow at around 2500°F (1370°C). In order to be able to complete the circuit, the current then flows through the safety gate valve through a bi-metal strip as the current heats it up.
Once the contact close on the bi-metal strip, the safety valve opens letting the gas flow through to the gas nozzle’s orifice to be then ignited with the igniter’s glow.
The gas line on the other hand comes from the utility company or a large propane tank outside and is piped through the walls of your home up to the shut-off ball valve behind the stove.
The stove is hooked up to the supply line at the valve and is fed directly to the oven safety gate valve. It is then fed through the burner where the glow igniter is already hot enough to light it up.
The power flows constantly through the igniter and the valve for as long as the thermostat doesn’t reach its set temperature.
Once the temperature is reached, the power source is cut off at the oven control button or the electronic control board circuitry stopping the gas flow as well, with the bi-metal switch opening and triggering the valve shut.
Note #1 - It takes between 30 to 90 seconds for a glow igniter to attain its prescribed wattage and for the bi-metal strip to activate the safety valve.
Step 1 - Observing the Burners in Operation
You have to determine where the problem lies within your oven, and since the oven cavity is often provided with a removable panel or panels—a bottom panel and sometimes covering a baffle plate (or flame spreader plate), underneath which you’ll get access to the oven bake burner and the ignition system unless the access is instead provided from the bottom drawer area.
On some ranges, you can have an extra broil burner at the top of the oven cavity, which may also need to be accessed.
It would be advisable to consult your owner’s manual on how to remove the panels and get proper visible access to the burners and ignition systems. Make sure all the burners and the igniters are exposed, then turn the oven on.
Step 2 - Oven Not Heating and Igniter Not Glowing
2.1 - With all the removable panels out of the oven cavity, make sure you have power at the outlet where the stove is plugged in with an outlet tester or a multimeter. If there isn’t any voltage present, check the fuse or circuit breaker. With the power restored, plug the stove back in.
2.2 - Switch on the oven control to warm the oven. Look at the igniters to see if they are, in fact, glowing. If they’re not, it could result from:
A) Lack of voltage at the igniter—from a defective oven control or electronic control board. Or
B) An open circuit from a defective igniter or from a defective valve, a broken or unplugged wire, or connection.
If you can measure the full voltage at the safety valve’s terminal, the problem likely lies with a faulty safety valve (probably a severed bi-metal band) or faulty wiring to the neutral side of the circuit, impeding the current flow.
Step 3 - The Control Board and Oven Control Switch
This next test must only be performed if you are extremely comfortable with troubleshooting live circuits—otherwise, call a certified technician.
3.1 - Secure one probe of your multimeter to Gnd (ground connection) to provide a good ground connection. Bring the second probe in contact with each of the terminals on the igniter.
A reading between 110 to 120 volts reading on one of the terminals indicates that the proper voltage is coming from the control board or the oven control—proceed to step 4.
If not, you’ll have to check the voltage coming from the control board or oven control switch and inspect the circuit’s wiring in between.
If everything checks out, you’ll need to verify the control board or oven control switch’s input voltage at its terminal. A good reading will indicate a faulty control board or switch and will require replacement, while a negative reading will indicate faulty wiring going back to the power cord.
Unplug the cord and take a resistance reading (Ohms) between the hot prong and the power input terminal of the control board or oven control switch. If it indicates an open circuit (∞ reading), you’ll need to investigate for unplugged, broken, or otherwise damaged wires and repair.
Step 4 - The Glow Igniter
From this step on, you must unplug the stove from its outlet to avoid damaging your multimeter or hurting yourself.
4.1 - With your multimeter on “Ohms,” take a resistance reading across the two terminals of the igniter. A good reading should be between 40 and 400 Ω—any reading higher than 400 Ω shows a defective igniter.
4.2 - Inspect the wiring leading to the safety bi-metal valve and measure it for continuity.
Step 5 - The Bi-metal Safety Valve
The way the safety valve works is that once the current starts flowing through the bi-metal strip, it will warm up and, once hot enough, will open the gas valve letting the gas flow through to the burner.
This occurs within 30 to 90 seconds, during which time the now glowing igniter located near the oven burner will ignite the gas.
The temperature sensor will keep the current flowing, thus the valve open until it reaches the set temperature of the oven. The temperature sensor then opens the circuit, stopping the current flow and letting the bi-metal strip and the igniter cool down.
Note # 2 - Some higher-end stoves have separate bake and broil burners with each their own igniter and use a “dual” safety gas valve, in which case both the bake and broil should be considered as having their own gas and ignition system.
Note # 3 - Dual valve should be considered as two different units when troubleshooting. Just because one side works doesn’t mean the other side is not defective.
5.1 - With your multimeter still on “Ohms”, take a resistance reading across the terminals on the safety valve. The resistance should be minimal. between 0 and no more than 4 Ω—anything more is a sign of a faulty valve.
5.2 - If you have a dual valve, repeat on the second set of terminals.
5.3 - If all is testing good so far, check the wiring running to the neutral side of your circuit for severed or damaged wires, corrosion on connectors, or unplugged connectors from terminals.
Step 6 - How to Test the Oven Sensor
The temperature sensor is a thermistor within a probe of a certain length and installed near the top of the oven chamber. Since its resistance varies with temperature changes, it can be quite easily tested with an ohmmeter.
You can simply have access to it by removing the cover from the back of the oven. The sensor is usually mounted on the top right-hand corner and has a plastic connector where it connects to the control board or the oven control.
6.1 - Unplug the temperature sensor by disconnecting the wire at the connector. With the multimeter on “Ohms,” measure across the two wires for its resistance which should be around 1150 Ω at room temperature. Therefore if your sensor measures above 1200 Ω or less than 1100 Ω, it should be replaced.
6.2 - Holding one of the probes on a grounded metal surface and the 2nd probe on each of the connector’s prongs will also tell you if the sensor is shorted to the ground, which will also call for replacing it.
Spark Electrodes System
Electronic ignition systems such as the glow igniter and spark electrode have been replacing the older style gas flame pilot lights systems.
The spark ignition system is basically a two-stage system with a spark generator module that produces high voltage pulses at very low amperage at around three sparks per second and is designed to ignite a low-pressure gas flow to a flame pilot light.
The pilot flame remains lit until the temperature sensor reaches the preset temperature of the oven and turns it off.
1 - With the stove plugged in, turn the heat on and check for sparks from the probe.
2 - Without any sparks present, the problem lies with the spark generator module—Check for 120 volts at the “power in” terminal.
3 - If you get a proper reading, replace the module. If not, follow but not specifically, the general instructions in Step 3 to troubleshoot the control board and the oven control switch.
Pilot Ignition Systems
A gas stove with pilot ignition has a continual flow of gas through the pilot, although with an actual but tiny flame in the oven. In this system, the thermostat controls the flow of gas to both the pilot flame and the oven safety valve.
When the thermostat is turned on, the pilot flame gets bigger and engulfs a close-by thermocouple bulb which directly controls the safety valve to open when it senses appropriate heat from the thermocouple.
With gas now flowing from the safety valve, the main oven burner usually lights within 60 to 90 seconds after the thermostat has been turned on for the larger pilot flame to ignite it.
1 - Make sure by lighting a top burner that the gas is flowing freely.
2 - With the oven turned off, check inside the oven for a tiny pilot flame. If it isn’t there, try and light it manually. If it doesn’t light up, the problem lies with the thermostat, which needs to be replaced.
3 - If you have a tiny flame at the pilot, turn the thermostat on and watch for the flame to “swell” up and get larger. Within 60 to 90 seconds, the burner should light up. If it doesn’t, the problem could be either with the thermostat, more likely, with the safety valve and its integrated thermocouple.