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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8164
Experience:  Furnace, A/C and heat pump specialist.
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I have a Rheem GRM about 10 years old. It goes through it's

Customer Question

Hi there. I have a Rheem GRM about 10 years old. It goes through it's cycle, it does ignite but the flame LED on the control board remains off, so the cycle stops. I have replaced the flame sensor and the control board, check all the connections and wiring to the sensor. What else can I try?
Submitted: 9 months ago.
Category: HVAC
Expert:  airheatman replied 9 months ago.

If flame light does not come on Most likely one of these things.

1.Wire to flame sensor shorted possibly touching metal

2.Ceramic on flame sensor cracked

3.Defective board

4.Wrong flame sensor

5. Wires not seated good in the 12 pin molex connector so not making good contact at board.

6.Furnace does not have a goof ground.

Since you have replaced flame sensor and board, check for good ground, short or skinned place on the orange wire and push the wires into the 12 pin connectors good.

Let me know if that helps. If not let me know if you have a meter to check micro amps .

We will want to see if flame rod is sending enough micro amps to board.See video below.

Expert:  airheatman replied 9 months ago.

Make sure these wires are seated good.

Customer: replied 9 months ago.
Hi, I tested wire continuity from the flame sensor to the board, all good. Placed mA meter in series (as in the video), red to the sensor, black into the wire. Powering on the furnace gave a 0.09mA reading, which didn't move once I got ignition.
Expert:  airheatman replied 9 months ago.

If you are only getting .09mA, that is not enough. Make sure sensor is in flame good. Also do you know for sure this is correct flame rod?

Expert:  airheatman replied 9 months ago.

You should have the 62-23543-01

Customer: replied 9 months ago.
It is the correct part. 0.09mA is before ignition and after power on. I noticed just now on a couple of tests I got a short jump in ma towards 0.2mA. I can't get the rod farther into the flame.
Customer: replied 9 months ago.
Rod position is fixed by it's length and a screw secures the one and only rotational position.
Expert:  airheatman replied 9 months ago.

The 2mA should be sufficient. The ***** *****ght should at least flash when you hit the 2mA. If the ***** *****ght does not come on, you may have gotten a DOA board, not unusual as most of these are imported..Can you exchange board?

Customer: replied 9 months ago.
Hard to see, but seems very close to burner opening. If the gas pressure is too high, maybe the hot part of the flame is too far. I'm not exploring another control board, seems v unlikely that it has the exact same issue. Furnace has been tested all summer and worked fine, this problem is new
Customer: replied 9 months ago.
Run more tests. mA begin to climb towards the last second before timeout, makes it to 10mA. Can I increase the timeout?
Expert:  airheatman replied 9 months ago.

No that is all built into the board for safety purposes.

Expert:  airheatman replied 9 months ago.

The items listed above are the only things I know of that will prevent the flame light from coming on. Is the furnace hard wired to a good ground or plugged into a receptacle? I have seen them work fine for years using a receptacle and for no obvious reason stop working unless we have a hard ground.

Customer: replied 9 months ago.
It seems wired up to ground, how can I test?
Expert:  airheatman replied 9 months ago.

Visually inspect to make sure ground wire is secured from gas valve to cabinet and furnace ground in disconnect power supply.

Customer: replied 9 months ago.
There is one earth cable that seems to come from the blower underneath and attaches to the the gas valve. There is a vacant connection point right next to it. I see no spare cables, and no other cables exiting the blower. How should the gas valve be grounded?
Customer: replied 9 months ago.
Summary - I seem to have two grounding points on the gas valve, only one occupied
Expert:  airheatman replied 9 months ago.

Usually thee is a ground that goes from gas valve to cabinet screw.Ground from inducer usually connects to it

Customer: replied 9 months ago.
I see a vacant cabinet screw that would hold a grounding wire. I will have to dash out and buy some :)
Expert:  airheatman replied 9 months ago.

Let me know if that helps.These things listed are about all I can think of that would cause the issue.I have been a Rheem dealer since 1989.

Customer: replied 9 months ago.
Grounding looks good now, but no difference to the results
Customer: replied 9 months ago.
the gordian knot approach. I moved the flame sensor away from the correctly installed position to a different position and held it and the mA probe in place with my hand without compromising the insulation. Voila, I have sustained ignition. What would make this work in the right place one day and not the next? Too much gas pressure, change in composition of the gas supply?
Expert:  airheatman replied 9 months ago.

Possibly gas pressure .Do you have a manometer of pressure gauge to check water column?