Hello All!

I have a Rheem Furnace model RGPH-07EAUER, serial # DF5D302 F1295 5487

Last week I noticed the house was getting pretty cool, and also noticed the heat wasn't coming on as often as it usually does. I went down to check the furnace and noticed the burners were not lit but the IDM and blower were running.

I turned off the unit and followed the directions that were provided from Rheem for troubleshooting. The step that seemed to always fail was the step after the Main Burner Lights up. The step is labeled, Main Burner Remains Powered and Lit. All the burners would always go out between 4 and 10 seconds. Directions recommended I clean the Flame Sensor, but that did not work. So I ordered a new one, and yet the same problem. The burners will never stay lit longer than 4-10 seconds, and they will try this for 4 times before locking the system down.

I've read that the flame sensor should always have a voltage around 90-100 VAC. Yet, when I test it from the flame sensor to ground (metal frame since I have no idea where the actual ground is), I get only 5 VAC, and 5.6 VAC when the burners are lit.

I didn't think the orange LED was ever blinking, but to my surprise it was. If I get almost to eye level with it, I can see a very faint and subtle blinking. When the burners do light up, the orange LED will blink twice, though this time very brightly, then back to the regular faint blinking that you can only see if you get right up to it. Could the 5 VAC I get when reading this connection be causing this faint illumination or is this normal? If so, then I'm curious why it is able to blink those two times very brightly when the burners are lit. During the reading it never goes over 5 or 6 VAC, even when the LED blinks brightly those two times.

Looking forward to any suggestions...

 

It sounds like the control board is ok since it's running the ignition sequence. The only true way to diagnose a flame sensor issue is to put a meter in series with the rod and the wire. One probe clipped to the rod and the other to the wire. It needs to be a meter that can measure ua (microamps). You need to measure several microamps of current flow. Probably around 3-5 ua.

Can you see the burners ? Make sure the rod is engulfed in the flame. Sometimes the burners don't all fully light and the rod is not in the flame.

 

I can see the burners easily and yes the sensor is in the direct flame. It only goes in one way on this model. So how do you test for the 90-100 VAC that suppose to directly power the flame sensor? I understand that you can test the micro amps, but I don't have a multi meter like that so I was hoping I could test it to make sure the IFC was providing the necessary VAC to the sensor. Is that not possible? If so, why not if it's suppose to be getting that range of VAC then shouldn't I be able to test for that voltage? Where is that 5 to 6 VAC coming from when I do test it.

Thanks again for the reply and suggestions

 

The AC you see is from the board. It varies from board to board. What is important is the current flow in the sensor loop. The AC voltage is rectified to DC when it passes thru the flame. That DC is what causes current to flow from the flame rod to ground. That's what must be measured.

 

Often it is the "ground" connection between the burner assembly and the main circuit board that is the problem. You could try adding a grounding conductor between the two and see if this fixes the problem. Usually the manufacturer will use machine screws with star washers between the parts and this also helps to maintain the electrical connection. If you see any wiring with round (eyelet) terminations that are bolted with star washers try disconnecting them and clean all surfaces of the sheet metal and the wire terminals with fine sandpaper, Re-assemble and make the bolts, terminals and star washers tight.

 

But doesn't 5 or 6 VAC seem extremely low? I thought so considering everywhere I've read has stated it is usually between 80 and 110. I've checked the ground from the burner itself and it's 001, which I believe is very good.

 

I tried to test it with my cheap meter which only can test current at 10A, and it always registered 000 no matter what, even when the burner was lit, which I believe is when it should read something.

 

You need a meter which can read micro-amps. If you are lucky your meter will only read into the milli-amp range which is 1000 times too high. Furd's comments about "ground" are spot on. Many, if not most, flame sensing errors are due to a bad ground connection.

 

On your control board there should be two green LED's and the one yellow/amber one. The yellow LED is flame sense condition. That yellow LED should not be on until there is a flame and then it should lock on solid yellow. Blinking yellow signifies a weak signal.

You don't have an ohmmeter that can measure the grounds. You'd need a micro ohmeter that could read well below 1 ohm. You'd need a ground measurement down to .01 ohm. When I suspect a ground problem I add star washers to any metal screws I see on the burner and metal frame. I also check to make sure the control board screws are clean and tight.

I already mentioned the rod needs to be IN the flame. The rod can be adjusted slightly if needed.

 

To measure for voltage to the flame sensor,
set your meter for volts AC,
unplug the flame sensor,
plug the red lead into the wire that went to the flame sensor
and put the black meter lead on ground.

 

I was finally able to get the burners to stay lit, but it turned out to be short lived. About 2 days later, it started doing the same thing again. The way I managed to get the burners to stay lit was a complete accident.

During one of my many test, I had turned the gas valve off, and when I realized the burners were not lighting this time, I was really puzzled. This is because the burners would always light up and burn, they just wouldn't stay lit. So I shut the system off, realized what I did and turn the gas valve back on. Well, lo and behold, the burners lit up, and they stayed lit...all freaking day! So, somehow toggling the gas valve off and on resolved the issue.

Well, about two days later, I noticed it was acting up again, so I toggled the valve switch again off and on, and it worked again for about a day. Unfortunately, the toggling quit working, so in my mind, I had it figured out, my gas value was going bad and possibly not regulating the gas flow. So I ordered a used one off eBay and replaced my old one. Damn thing ran for 3 days straight, no issues. Even the yellow light stayed solid, as before it would always blink meaning only a marginal flame detected. I was ecstatic, my wife was proud of me once again. Then it happened again, I felt cold air coming out of the vents one morning. Went to check the furnace, and the burners were out again. So, I toggled the gas valve on/of switch as I had with the old one. The burners worked for about 10 minutes then they were out again. Now I was right back where I started.

So, still confident I could resolve this, I was certain the gas coming through the pipes to the gas valve must be getting dirty, so I removed that little 3-4 inch pipe that suppose to catch all the debris and moisture in the pipes. I was expecting it to be full after 20+ years of use, but it was empty. So, now here I am, really lost as to what else to try or why the anomaly with the gas valves.

 

I also replaced my flame sensor with a new one, even though my old one looks fine. I noticed righted away the yellow LED was solid finally, but it was short lived, and about 10 seconds later, it started blinking again.

So I've noticed two patterns here that I find interesting:

When I replaced the gas valve with another used one, the yellow LED was solid, though for only about a day before it started blinking again.
When I replaced the flame sensor, the yellow LED was solid, though for only about 10 seconds, then it started blinking, and has blinked every time thereafter that I've retested.

How does these two different components effect the yellow LED in this way? I'm thinking this has to shed some light on the issue.

 

The flame sensor rod is a solid piece of stainless steel. They don't get replaced unless physically damaged. I have never changed one.

The circuit here is not a mystery. The AC voltage comes out of the control box on the flame sense line. The rod has an AC voltage on it. When the flame starts..... the flame creates a bridge between the flame rod and ground. That bridging process thru the flame converts AC to DC and the flame rod then becomes shorted to ground. That short is measured in microamps. Without connecting a meter.... there is a lot of guessing what's going on.

There are two things here that come to mind.....
1) the burners need to be pulled out and cleaned.
2) check ALL burner screws for tightness. Any loose or rusted screws are trouble.

 

Thanks for the reply!

I have taken the burners out and they arn't dirty, though the two in the middle are fairly rusty. The flame sensor is connected to the last burner on the far left. That burner has no rust and is clean. Checking the ohms from any point around that burner to ground is always 001, which I believe is very good. So if I have good ohms, what else could be interfering causing the yellow LED to always blink. What gets me, is when I first replaced it, it stayed solid for about 10 seconds. How could it stay solid if the connection was bad? That's why I'm thinking it's not the connection but something else. The only factor that has made any real difference is replacing the gas valve, though it ended up doing the same thing, but at least I got a couple days out of it, which nothing else has even came close too.

I would though like to really test the mA from the flame sensor. Maybe I can pick up a premium multi-meter at the store and return it after I test it

 

The important thing with the burners is the carryover port. There is one between each burner. It carries the flame from the first burner where the igniter is to the last one where the flame sensor is.

You don't even need a premium meter. Many of the basic ones have the ua scale and a test meter is a good thing to have around. Here's a real buy from the Depot. Only $25.
Klein-Tools-Manual-Ranging-Digital-Multimeter-MM300

 

I ordered the multi-meter you recommended and received it yesterday. Testing the flame sensor, the mA were always a steady 2.9-3.0. While testing multiple times, I would observe the yellow flame sensor LED on the IFC. It almost always just blinks, as I have stated in my previous posts, but occasionally it will be solid (which means a good flame, while blinking means a marginal flame). So one time when the burner started, the LED was solid for about 8 seconds, yet the mA results never fluctuated as I would have thought. It always read between 2.9 and 3.0, well, except during the initial startup when the burner first lights, it reads 1.5 for about 3 seconds (this is before the LED even lights up), then reads 2.9-3.0 from then on until the burner kicks off, then back to 0. So, I believe my flame sensor is fine, would you agree? I have noticed that the burners will kick off even when the flame sensor LED is solid, and when I do manage to get it to run for long periods of time, the flame sensor is almost always still blinking.

I thought the pressure switch may be releasing while the burners are lit, so I shorted the switch and still the same issue. I also verified the diaphragm was closing by checking the continuity over the switch during the entire process. It never opened, so no issues with vacuum. I also verified the high temp switch, and shorted it for testing purposes, yet same issue. I also sanded and cleaned the entire burner area including the burners, and verified I had good ohms from any place in the burner area to ground.

As mentioned in my previous posts, the only thing that I have done that has made any difference and allowed us to have heat for at least 24hrs was related to the gas valve. The first time was by accident, as I mentioned in my original post. By just turning the gas valve off and back on, the burners stayed lit for the rest of the day. Unfortunately, this was shorted lived, and by the next day I had to turn the knob off and back on again, and it stayed lit for a couple hours. Eventually, toggling the knob made no difference. I ordered a new, but used one on eBay. Hooked it up, and for about 3 days, everything seemed back to normal, then one morning I noticed the burners were not staying lit again. I toggled the gas valve knob off/on, and the burners stayed lit, though this time only for about an hour maybe.

Currently, it makes no difference now when I toggle it, the burners will only stay lit between 4 to 23 seconds, so I’m really baffled as to what to try next. I want to order a new gas valve, but I’m worried that whatever is happening is damaging the gas valve in some way. I mean obviously the gas valve still works because it will light the burners, but I feel like something in my setup is causing something in the gas valve to gradually fail.

 

Yes.... 2.9-3 ua is fine.

Your board can't hurt the gas valve. It either feeds the valve 24v or it doesn't.
The link below is your manual. The last two pages are two diagrams.... one for spark ignition and one for hot surface igniter. Which ignition source do you have ?

The manual has a thorough diagnostic chart but you've tried most. One point got brought up several times and that was main power wiring ground to the furnace. Do you have romex or bx feeding your furnace ?

The next step is to use your voltmeter set to the scale over 24VAC and check the voltage from pin 2 (yellow) to pin 4 (blue). on the 9 pin plug. It should be there as long as furnace is calling for heat and burner is running. It may be a little tricky to get the probes in those small pins holes. Give it a try.

There is an extra part in the burner circuit used on certain installations. It used with downflow and horizontal air flow furnaces. Apparently not on upflow furnaces but it could be there too. It's not a high limit.... per se. It's a heat assisted limit control and monitors the air temperature in the blower housing. It turns the gas valve off and on based on air temperature.

Check those two connections first.
Furnaces/Rheem/Ruud_GPH, GPJ, GLH, GLJ.pdf

 

First off, I want to thank you for assisting me with this as I know your time is valuable. I also want to apologize for the delay in getting back to you. I thought I had instant email notification setup for this thread but apparently I didn’t, or I have to select it each time I reply. Not sure, but I will definitely keep an eye on it from now on.

Anyhow, I thought I would share with you some developments that transpired over the last two days, before being aware of your reply. In a nutshell, I had it working great for two days! During my persistent testing and researching, I came across a video on YouTube that really got me thinking about what could actually be the problem. I keep thinking my ground is fine, but after watching the video, I realized there is much more to checking ground, and that the flame sensor is affected by fluctuations in the ground.

In the video, he states that you need to not only check the DC mA from the source side (which is where I was getting the 2.9-3.0 readings), but also from the ground side. And, what really got my attention, is he said this ground wire is connected to the gas valve, and from the gas valve, another wire connects to the IFC board, which then tells the board a flame is detected. He said it’s important to make sure you check the DC mA between this connection.

Unfortunately, I had no luck getting any amps to read by doing this, which really puzzled me. But, something miraculous happened from this test, which was by accident once again. On my furnace, there is a short 6 to 8 inch ground cable that goes from the gas valve to the frame of the inducer motor. During my attempts to test the DC mA between these points, I disconnected this wire, and well, never plugged it back in. Well, to my amazement, with that secondary ground wire disconnected from the gas valve (I call it secondary ground since it’s not as important as the main ground, plus I really don’t know what you would call it) the burners stayed lit. The unit worked properly for the next two days, until this morning when I noticed it was chilly again. I checked the unit, and it was doing the same crap as before.

Now though, it seems it will stay lit longer than before (before removing the secondary ground). First attempt, the burners stay lit about 1-2 mins, while the remaining three attempts (before lock up) are only about 23-25 seconds. I noticed a pattern this time with the last three; they shut off exactly when the blower kicks on. Another thing I noticed this time around, is during the first attempt, the flame sensor's LED is actually solid, that is until the 23-25 second mark, or when the blower kicks on. This occurs only on the first attempt though, as the remaining 3 attempts, the LED is always blinking (marginal flame detected). At first I was puzzled by this difference, but then I realized the blower is always running after the first attempt. So, is it possible my blower is stealing the amps that the flame sensor needs or does this seem normal?

Now, to finally address your questions.

I have a hot surface igniter and the wiring is romex. I will try to test those two pins for 24vac. Thank you very much for the manual, I will certainly put it to good use! I don’t think I have the heat assisted limit control your described but I will double check.

I have two questions I'm concerned about that I hope you or someone can answer for me:

When checking the neutral and ground for voltage, I get the following readings: 0.1 at startup, 1.1 when HSI ignites, and 0.6 when blower is running. Is this normal or should it always be zero? I think I read somewhere that if current is present there will be a small voltage when testing ground to neutral.

I know we agreed the flame sensor seems fine, but I’m confused about one thing regarding it. I’m told the flame sensor is always energized because it is always checking for flame, for obvious safety reasons. The flame sensor then should always have a voltage around 80-100vac, yet I have never measured more than 5vac when I test mine. And if it had 80-100vac, wouldn’t I feel that when I’m disconnecting and reconnecting the flame sensor wire to the actual flame sensor rod, as I’m usually touching the metal frame during the process? And yes, the unit is usually powered on when I do this.

Below is a link to the YouTube video if you want to check it out. Strange, because all the reading I have done thus far, no one but this guy in the video has mentioned the need to check the DC mA on the ground side. I'm wondering why this is so, and also why I'm not able to get any readings when I check it this way.

Furnace Flame Sensor Testing and Flame Rectification Troubleshooting!
https://youtu.be/LtfghUYfl-4

 

I tested pin 2 and pin 4 successfully. I read 24.0 - 24.1 vac when the burners lit, and 0 when they went out.

I haven't messed with the furnace since my last post, so it's been seating there for awhile before testing it just now. When the burners first lit this time, they only stayed lit for about 21 seconds and about 8 seconds each time thereafter (3 more attempts before lockout), which was much less than the 23-25 seconds I had posted last time. I didn't see anything that resembled the heat assisted limit control you mentioned.

Looking forward to your thoughts and any answers for my previous questions.

Thanks again!

 

Testing from the ground side, I cannot register any DC uA. It's always 0.00. I confirmed the signal wire from the IFC board to ground is 0.00 ohms, and checking the common to ground I get 0 vac, so what could be causing this? Is it normal when testing the flame sensor for voltage to get only 6 vac, b/c it seems pretty low? When I do this test, it also causes the blower to come on and the unit reports an Unexpected Flame Detected. Apparently the flame sensor doesn't like me testing it for voltage.

None of this seems normal to me, I would love to hear from someone their thoughts regarding this.

 

What he says in that video is a way of testing but the problem is your IFC has multiple grounds to it. There is no way to read the microamps of the flame sensor without opening all the ground lines. You opened one and saw 0v because there was another ground that was still connected. I've never been concerned measuring the ground current.

Just some random things to check.
1) make sure the ground wire of the romex cable is solidly connected to the furnace frame.
2) make sure the romex hot and neutral are correctly connected in the junction box... not backwards.
3) when the furnace lights..... make sure the rod is always in the flame. The flame can lift from the burner and that will cause a loss of flame signal.
4) check the AC voltage to the flame sensor with it disconnected from the rod.
5) remove and reinsert the 9 pin nylon connector in the board several times. I little bit of contact cleaner on the plug pins wouldn't hurt. If you spray the pins.... it will transfer to the receptacle when plugged in.

From what I've found.... the AC voltage to the flame rod should be around 80vac.
After trying what I mentioned.... it leaves the board.

 

Hi There,

I have a very similar problem, flame sensor shows 2.5 ua, the furnace control board is just replaced. The furnace works for a few hours then the problem started. The cycle goes through until flame is present, then after few seconds shuts off. The sensor is cleaned and is in the flame, the current is there going to the board from the sensor, as mentioned 2.5 ua.

I am now thinking the board, although new might be bad. What did you eventually do to solve your problem? Please help.

 

Welcome to the forums.

You need to confirm that the current you are measuring is enough for your particular control box.
It is enough for some but not all controls.

 

I checked the control board data sheet and it says minimum 1 uA current required, so I am confident this is not the flame sensor, I just replaced the sensor with a brand new one with the same results.

 

The flame sensor is just a piece of stainless steel rod...... nothing more. If it's clean.... it's good.

If the flame current is maintained at 2.5ua and the unit shuts down..... it only leaves a defective controller.
Be sure the 24vAC to the board is not dropping out. That could happen with a defective safety sensor or possible corroded connection.

 

Pj when checking that flame for vac one lead in the wire where should we touch the other lead ? Earlier I only got 45vac but I touched the other lead on common from the thermostat wires sure that wasn’t correct

 

Faulty board was the case, thanks to Modify hints, I found a replacement board on Kijiji for $150, replaced it and its fixed. Saved me over $1K and time dealing with greedy HVAC companies.

 

This is an old thread but just want to say that the same thing happened to me: off/on in 2-4 second intervals. Furnace had been serviced professionally for past 3 years. Last month a young crackerjack tech found my ground wire was loose. Tested .3uA before connecting, 2.3uA after connecting. No problems since. Someone else experienced the same and many mentioned the ground...for future reference. I'm currently waiting to see if the company will refund my service call since no tech found it in the prior 3 years of service/hands-on.

 

So one day the furnace wasn't working It cycles through and quits about 4 seconds after the flame is on. Cleaned flame sensor and didn't work changed flame sensor and it is in direct flame didn't work no loose wires Checked in line the flame sensor, when flame hits it, goes up to 7.9 m amps. The ground reads 0.05 No codes on board but the flame led yellow light never comes on or flickers had sevice guy come out and scratched his head and said everything is testing good and has no idea what's wrong. Cleaned the burnes but there really was no rust I changed the mother board and svts the same way it is a conquest 90

 

Welcome to the forums Budman.

This thread is getting too long so I will be splitting it off and making it it's own thread.
Is this the same exact model as the original poster ?
7.9m is that 7.9ua ?
If you had 7.9ua you'd have a flame there and the flame LED would be on. So I'm not sure where that number came from.
Is the flame sensor rod directly in the flame ?
A very common problem is a rusty burner with rusty screws. The burner MUST be grounded. The control board must be grounded.

 

Thank you for your reply.
yes exact model.

Furnace cycles and lights up for 4 seconds and quits.

1. No codes on board
2. The flame sensor led never lights up
3. Cleaned flame sensor
4. New flame sensor
5. Checked grounds and good, even ran new ground
6. Cleaned burners even though no rust
7. No blockage on intake or exhaust
8. Multiple ohms reading all test good
9. Changed motherboard
10. I Broke the ignitor 🤯
11. Change ignitor
12. Bypassed thermostat
7.9ua once the burner lights the burner is grounded and I have the board hooked up the same as the original

 

What part number controller do you have in there ?

 

62-24268-01
replacement-03
Is it possible the new board is bad too?

 

Yes, it is possible. Sometimes you think and the paper says the board is upgraded to a new model and you use that board to find out it is not working. It happened to me, I bought a brand new board which said it would replace my board, but it did not work. The flame senesor was giving the current, but the board did not care about it. Changed the board to a used one I bought and voila everything worked. Did you replace your board with the exact same model?