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I seem to have a working spark ignitor although I can not see it when installed. When installed outside of the furnace for testing it sparks when it should when the gas valves clicks open. I can always (so far) light the the gas burner with a BBQ lighter when the gas valve clicks open. However, about one time out of ten when the thermostat calls for heat the furnace will try to ignite but fail and must be reset, After reset the furnace will ignite about one out of three time. After not lighting on a cold night I resort to the BBQ lighter when I hear the gas valve click in it's sequence and the main burner lights every time.

I've checked all the obvious items like the flame sensor and ignitor device itself and all the safety air switches and condenser switch; clogged filter and exhaust. The blower motor and purge motor.

The unit runs fine when it runs. The frequency of not lighting seems to be increasing. I hesitate to call an expert as the problem is intermittent.

Is there a possibility the furnace control board is not providing a strong enough spark? Could the spark gap on the ignitor (brand new) be too large/small? The gas outlets from the manifold pipe seem all clear and I vacuumned the burners. As I said when it works it works fine...

I ran a separate ground wire from the main gas supply pipe to the ignitor mount to assure (?) a good ground.

The present gap for the spark to jump is about 1/8". I'm old and do not hear well so I don't know if the spark "cracks" or not; I'd say the spark when tested, is about the same as on our gas range burners.

Thanks for any help. Unit is a Rheem RGRA-09EZANJ 90 plus upflow Classic about 15 years old; since our home was new. I'm a long time home builder. The installer is long retired. This is our first problem. There is a electronic air cleaner and power humidifier and a/c.

  • Is there any adjustment for the position of the spark igniter? You would seem to have experience just below that of an expert. Even though this is intermittent, an expert might know exactly what to look for. – Jim Stewart Feb 14 '18 at 16:54
  • I am wondering if you have moisture in your gas line. Some installers do not install a "drip leg" just prior to the device after the shutoff valve is my preference. It only takes a little moisture to reduce the gas flow that may make the pilot weak. My last home had this problem I added drip legs and on the lowest one in the house at the furnace I usually had to empty the drip leg every year and sometimes 2 times. Something to check into. – Ed Beal Feb 14 '18 at 20:35
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I would give about an 80% chance that the board is not putting out the proper voltage and should be replaced. Other problems could be a bad spark wire or connection or poor positioning of the electrode. It is not the flame sensor or it would light for a few seconds and then go out.

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Flame rod sensor the led on control board should give you a a code on what code is coming up from ok that you can ellinate the cause jump the r and w on panel where the thermostat cables plug in at furnace if it turns on it’s your thermostat seen that a lot when people upgrade their thermostat and don’t label their wires

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