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Flame sensor hack

toyrist Member Posts: 1
Hello DIY,

Gas unit: 1988 Janitrol Goodman GUI 125-4 rev s input 125,000

I had an issue with my gas heat unit not turning on. I proceeded to clean the flame sensor, and the unit responded somewhat but it was still having problems detecting the flame from the pilot. The flame from the pilot has always turned on and that does not seem to be the problem. I initially thought that the flame sensor was dirty so I cleaned it, nothing. Thought it was defective so I bought a new one, nothing. The new one did not worked as expected either. I started investigating more and inspecting the unit and realized that if I moved the flame sensor closer to the pilot flame (actually getting it off the intended place and manually putting it close to the flame), the unit would go thru the motions normally (turn on main gas, etc). It seems that the flame from the flame sensor is not "spreading" enough to activate the flame sensor at the distance it was designed for. Now this unit is old (30 years) and rusty. It worked for two winters without a glitch since I moved to this old house. This is the third year and it is when it is giving me trouble.

So what I did was to bend the flame sensor with pliers to have it closer to the flame (see pictures). I bent the old sensor and voila! the heater unit is now sensing the pilot flame and turning on the main gas immediately after. blower turns on, etc.

the one one the right is the stock photo of my pilot and flame sensor (circle red notice the gap between sensor and flame).
the one on the left is my system before I bent the sensor (was working for 2 years, stopped working this year)
the one on the bottom is bent flame sensor (working now)



(1) is the flame sensor capable of withstanding being closer to the pilot flame, heatwise or otherwise? I would suppose so since the flame sensor is next to the main flames once the unit goes on. it does get hot in there.

(2) is the flame sensor too close to the flame that it can "overheat" the electronics on the other side of the flame sensor? It is literally touching the pilot flame once the thermostat turn it on.

(3) i thought flame sensors were delicate. I bent and mistreated the old one and is working. I had also cleaned it with a fine wire cloth (didn't work) and to an extreme scrapped it with a blade a lot beforehand trying to clean it (back when I thought the sensor was dirty). The old sensor is really beat up. How come is still working?

(4) how come the flame heat from the pilot is not "reaching" the flame sensor any more to turn on main gas? Is the pilot system somehow "plugged"? It definitely worked without a hitch for the last two years. How come it got "plugged" this year?

(5) any other comments?

Thank you guys,

TL;DR: bent my flame sensor so it is able to detect pilot flame. is my unit going to blow up? Look at picture


    JUGHNE Member Posts: 11,058
    The flame sensor is one half of a flame rectification circuit.
    A ground path is the other half.
    It does not feel heat, it instead passes a small electrical current thru the fire itself, so it has to be in the flame. But the current has to be able to return to the ignition module thru the fire and the ground circuit for the module to realize that there is actually flame (fire) to allow the main gas to come on.

    Your pilot burner could be partially plugged not allowing flame to touch the original location of flame sensor.
    Bending the flame sensor rod could crack the insulator portion and also cause problems.
  • Tim McElwain
    Tim McElwain Member Posts: 4,621
    Clean the orifice in the pilot and put the sensor back to its original position. Check the microamps to see if you have between 2 to 10 microamps. Normal is 3 to 5.