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Hello,
My Carrier 58mvp Gas Furnace has suddenly started intermittently firing. There is plenty of gas pressure at the valve but will continue to run constantly without too much heating properties. There is a flame in each of the burners. Could someone please explain what the flame sensor does and how it functions? The error code that was diplaying at times were error code 34 (ignition proving failure) All troubleshooting remedies were used according to the manual given and were all proven good. This is an intermittent problem and works for a day or so then will not fire. Then suddenly will start but see weakness in the burner flames. Then once again it will fire and work as supposed to. Any suggestions w/out having a service call.
Thanks in advance.
Doug
 

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Try replacing the flame sensor, be sure the gas valve is opening and check the amp on the valve a few times during the time that it opens.

Sometimes a valve may stick long enough to delay the start, this can be shown in the amps. You may have to do it quite a few times in order to get it to fail.

Also shut the system down for a few hours, this will allow the valve to cool down. again try the amprobe test and see if the readings chenge.

You may be in for a gas valve, and or a board.

Bernie
 
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There is a small rod which is in the burner flame.A gas flame has a electrical charge the flame sensor passes 3 to5 microamperes through the flame to the burner (ground). The sensor or flame rod will build up a coating on it . I can't remember the exact name for it.Remove the sensor and clean it with seelwool this removes the coating.It does not take much to make the signal drop below what it should be.Also if you watch the flame if the flame pulls off of the burner this will also cause a flame failure.
 
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drpsr69 said:
There is a small rod which is in the burner flame.A gas flame has a electrical charge the flame sensor passes 3 to5 microamperes through the flame to the burner (ground). The sensor or flame rod will build up a coating on it . I can't remember the exact name for it.Remove the sensor and clean it with seelwool this removes the coating.It does not take much to make the signal drop below what it should be.Also if you watch the flame if the flame pulls off of the burner this will also cause a flame failure.
That is steelwool.
 
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