Kenmore Gas Oven mdl. 790.70502013 will not stay lit, bad ignitor?

[Chris F]

My oven is a Kenmore 790.70502013 (single oven burner, single ignitor, single gas control valve)

The oven burner intermittently ignites and it will not stay lit long enough to come anywhere close to usable temperature.

Symptoms: Turn oven on to bake/broil. The glow ignitor will glow, the burner will usually ignite in 60-120 seconds, however, the ignitor will stop glowing shortly after burner turns on (within 5 sec to 2 min), when the ignitor stops glowing, the gas supply turns off, and the burner goes out. The oven does not relite after this happens. Unplugging the oven for several minutes then trying bake or broil again will result in the same this happening again.

I have taken it apart and tried all the tests I could find online which include:

• ·         All gas supply valves are fully open. Stovetop burners work perfectly fine, indicating the main gas supply is not the issue.

• ·         Glow Ignitor Tests: The removed, isolated ignitor showed to have continuity. The resistance of the ignitor was measured to be 336 ohms. I do not have an amp meter to measure the amp draw of the ignitor.

• ·         Gas Control Valve Tests: The terminals on the gas control valve have continuity. The resistance between the gas control valve terminals (with ignitor removed) was measured to be 2.5 ohms.

• ·         Voltage Supply: The voltage supplied to the gas control valve and ignitor was measured to be ~118 VAC when in bake/broil mode.

• ·         Temperature Sensor: The disconnected temperature sensor was measured to have 1069 ohms of resistance at room temperature, suggesting that it is functioning properly.

• ·         Relay Noise: When the oven is set to bake/broil you can hear a relay switch. The ignitor is supplied with AC voltage and begins to heat. Then the gas control valve opens, and the burner ignites. Shortly after you can hear the relay switch, the ignitor stops glowing, and the gas turns off.

       I am thinking that it may be a failing ignitor? From what I have found 336 ohm resistance on the ignitor is higher than it usual?

       Can a failing ignitor cause the oven to ignite, run for a short amount of time, then turn off? Do you think it could be the oven control board instead of the ignitor?

       Any advice would be greatly appreciated as I am planning on ordering a new ignitor but it is a $80 part for the OEM version.

 

[16345Ed]

If power is being cut to ignitor prior to reaching temp then it’s likely a control board issue ( that relay seems to be closing too soon) or a sensor issue. 

Does the ignition occur within 45-60 seconds of setting bake?

[Chris F]

Hi 16345Ed,

The ignition seems to occur within about 70-100 seconds. Once ignited it will turn off within 20-120 seconds.

I seem to have to let the ignitor cool down for 5-10 minutes before I can set it to bake where it will attempt to ignite again, which results in the same thing.

Somebody else suggested that the ignitor may have a break when it heats up and looses continuity, so they suggested replacing the ignitor.

Do you think it is the control board instead of the ignitor? Do you know of any additional tests I can preform on the control board?

Thanks for the help!

[jasonsvctech@gmail.com]

 

13 hours ago, Chris F said:

• ·         Glow Ignitor Tests: The removed, isolated ignitor showed to have continuity. The resistance of the ignitor was measured to be 336 ohms. I do not have an amp meter to measure the amp draw of the ignitor.

   

 

Your resistance on hot surface igniter is way too high. 336 ohms is literally triple a healthy reading. Replace the igniter. That high ohm reading will prevent current from getting to the valve and completing the gas circuit leading to failed heating issues. I replace 150 of those a year so I have the ohms memorized. Any hot surface igniter will do. If the metal frame doesn't fit you can carefully remove the new igniter (very brittle) from the metal sheath and put in the old sheath. You can get hot surface igniters on Amazon for $15. 

As the igniter heats up then additional radiant pressure on the electrical circuit causes an intermittent open on the igniter circuit (failed electrical circuit) which collapses the gas valve circuit leading to misfires. The software on the control has difficulty interpreting what is going on during such a misfire.  

Replace the igniter and you should be good to go. You can interrupt the circuit to test for sure. If you get 120VAC to the igniter circuit then the control is fine. The amp draw is minuscule.  250-500 MA possibly.

 

Thanks,

Jason

 

 

 

[Chris F]

9 hours ago, jasonsvctech@gmail.com said:

Replace the igniter and you should be good to go. You can interrupt the circuit to test for sure. If you get 120VAC to the igniter circuit then the control is fine.

 

Thanks for the help Jason,

When I initiate bake the igniter circuit gets ~120 VAC, measuring w/ a multimeter from the back of the control board where the two wires that feed the igniter circuit come out (yellow and white). The 120vac stays constant until the relay clicks (~30-120seconds after ignition) and the circuit goes to zero volts. The igniter is glowing when the relay clicks.

So I will try ordering the igniter tomorrow like you suggested. Thanks!

[jasonsvctech@gmail.com]

A number of times when I replace the igniter the old one glows orange. The problem is that the resistance has gotten so great that it has mopped up all the intensity of the circuit and isn't allowing enough of a flow of electrons to the gas valve preventing it from opening or confusing the control. These can sometimes be tricky though too.  The software on the control unit is monitoring the intensity of the circuit as a way of verifying that the flame has ignited.  It could be that with such a high ohm reading that the oven control software is triggering an ignition failure response. You may have other issues too. But no matter what, you have to start somewhere. Rarely there are multiple problems but those always have to be solved one at a time. The cheapest and easiest thing to replace is the igniter first.  The only time that I would consider the control bad without replacing the igniter first is if I didn't get 120 VAC when the circuit is interrupted at the igniter and I have heard the relay click in on the control meaning the control is not sending the power down even though it should be. If you get zero volts across the leads but get 120 VAC from one lead to ground (check both) then you could have a gas valve issue instead of a control issue. The gas valve provides the completion path for the circuit. If you get an open or high ohms across the gas valve then it could be bad also.  You should also ohm out the gas valve coil.  It should appear to be a short or no more than 10 ohms.  The coil should appear to be a direct short to the machine neutral which could be referenced all the way back to the plug. The positive 120 VAC delivered from the control passes through the igniter and travels on to the gas valve where the circuit terminates at the machine neutral 0 VAC.  If the igniter is 3-5 years old or older and you haven't had any power surges or known gas problems (lots of condensation in gas or a bad home gas regulator from your gas supplier) then likely the igniter replacement will solve the problem for you entirely.  Since you have said the flame lights, I doubt you have a gas valve issue or a control issue but until you have a healthy igniter in the system other problems may still be hidden.

 

Cheers,

Jason

[Chris F]

Thanks for the follow up information!

Getting a much better sense of the circuit. I didn't think to check the gas valve coil. Definitely going to grab a new igniter tho.

Appreciated,

Chris

[Chris F]

Just wanted to come back and update this thread in case anyone stumbles across it in the future.

After additional troubleshooting I noticed that the control board would stop sending the 120v to the igniter circuit after random amounts of time. The oven would not beep that it reached the desired temperature when it would shut off the voltage to the circuit, it would just randomly trigger the relay. It would do this with the igniter installed and when the igniter was completely removed from the circuit.

This lead me to believe that the control board was bad instead of the igniter. So I replaced the control board and the oven has been working perfectly ever since.

I replaced it with an "Electrolux 316455430 Frigidaire Clock/Timer" purchased on amazon.

Thanks for all of the advice, it really helped me isolate the problem.

[16345Ed]

Thanks for wrapping it up for us!!

[Hiroshi]

Simple rule: if an igniter takes longer than 60 seconds to trigger the gas safety valve: it is "out of threshold" and requires replacement. The only exceptions to this rule have been residences experiencing brown-out voltages in their neighborhood, in the 70-90 VAC range, during peak summer usage or machines with floating neutral issues. 

Edited May 3, 2019 by Hiroshi