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Heater problem On the GMPN120-5 heater under the Status Column 5 blinks =Equipment Problem False Flame Sensor, Under the Cause column it says Sticking Gas Valve. When the heater tries to cycle on the Exhaust fans runs after 30-45 seconds, the Ignitor glows and the Gas valve clicks the the burners will light. I have checked with a DVOM and 24 volts is present when the burners are lit, after about 5 seconds I loose the 24 volts and the valve closes and the burners turn off. I have also checked and cleaned the Grounds just to be sure. Thanks for your help. jg

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  • jbg36 Dec 10, 2008

    False flame sensed


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The first thing I would look for is a blockage in the gasline, or at the gas valve.

It sounds like you are not getting gas to the ignitor/burners. This would cause it to obviosly, not sense flame.

When a unit does not sense flame, it will shut of, and usually try again up to 5 times (depending on brand/model)

So here's what happens in that scenario.

Call for heat.
Inducer motor kicks on, the sensor detects the inducer motor is working, and the ignitor starts glowing/sparking (depending on type of ignitor)

It will then send gas through the gas valve and ignite.
If the flame sensor does not detect flame, the glow coil shuts down, the gas shuts off, the inducer shuts off and you get your error code.

(Some units will then send on the blower motor, and you have to cut power to reset.)

Do you have a copper line with natural gas?
If so, replace it with stainless steel or black iron.

Coper apearantly reacts with the aditives in natural gas and tends to form a gray ashy substance that builds up in the copper tubings walls and eventually cloggs gas valves.

At the inlet side of the gas valve, there should be a screen to catch such things.

Turn off the gas, turn of the power, and remove the gas line going to the gas valve. Look for anything clogging that area, also look for kinks in the gas line.

Remember to use a "flamable gas approved" pipe dope or thread tape when reinstalling the supply line.

Lets see what you find there and then we can continue the diagnostic if needed.

Posted on Dec 10, 2008

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Furnace problems

On - OK
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2 Blinks - Closed pressure switch. Check pressure switch (stuck in closed position).
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4 Blinks - Open limit switch. Main limit or aux limit are open. (My comment - Means overheating in chamber. Often result of blocked intake air. Bad filter. In my case, plastic wrap had been sucked into the intake. )
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