furnace will not stay lit Ruud UGPH 12EARJR

Old 10-27-16, 05:49 PM
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furnace will not stay lit Ruud UGPH 12EARJR

Furnace attempts to start but shuts down.

Sometimes the induction blower runs, the gas comes on, the igniter ignites the gas, the burner lights for a minute or two, then just as the main blower starts up, the burner shuts down. The blower will run for a few minutes, then stop and will repeat start up cycle. When it repeats the start up it will vary between two different patterns.

When it attempts to start up again it will repeat what it did above or it will go through the start up but will shutdown just as the gas valve opens but before the gas can flow. The igniter may or may not get off one spark. When the valve opens everything closes down instantaneously with its opening. When this happens it usually will attempt to start up again immediately with no wait time.

It continues cycling like this continuously with no shut out time even if the burners light up.

I cleaned the flame sensor with some steel wool and it made no difference. It was replaced last heating season.

Thanks for the help
Old 10-27-16, 06:36 PM
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Your problem certainly sounds like a flame sensor failure. First check to see that it is tight and that the wire is properly connected at each end.
You could then remove the flame sensor and fire the furnace. If it stops as you have described, either the sensor or the circuit board is bad.
Old 10-27-16, 09:56 PM
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Welcome to the forums.

You are describing a defective control board. After the flame extinguishes the board should immediately go into a purge mode to clear out raw gas. The fact that it's trying to relight immediately is a problem.

There should also be a sight glass in the blower door where you can look thru and see the flashing trouble code.
Old 10-28-16, 12:53 AM
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Thank you for the info.

The connections on the flame sensor are tight.

The control board shows no trouble codes. It has two green lights that are steady on. No blinking codes.

Should I assume that it is the board?

Thank you
Old 10-28-16, 12:11 PM
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You need to determine why the burners are shutting off.

For example, the thermostat may be shutting off the furnace, which would turn off the burners and display no diagnostic code.

To check that as a possibility, use a multimeter to verify that the 24 VAC to the W terminal remains on. The thermostat is calling for heat whenever the W terminal; is energized.

If that stay on, you need to verify that the pressure switch isn't opening, which will also shut off the gas.

Measure the DC microamps flowing along the wire to the flame sensor to see if that at a level that is reliable --- usually 4-5 microamops is good.

IF ALL those items are working properly, you have a bad circuit board.

Diagnostic codes are often very helpful in diagnosing problems like this, but if you have a bad board perhaps the diagnostic lights aren't doing their job either.

It may be that you can't do a competent job of making these various tests, which wouldn't surprise me. If you can't do them, find a good repairman who can do them for you. The most important thing you need is and ACCURATE diagnosis of the problem.

That's more important than doing your own DIY job, in this instance.

That's my assessment, anyway.

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