Rheem xe 80 intermittent heat

[RHEEMXE80]

My Rheem XE 80 Gas furnaces is having a few troubles. When the t'stat calls for heat, the furnace goes through its startup process, the purge fan comes on, but about half the time the igniter doesn't glow, so the gas doesn't come on, and so no heat.

Some of the time it does work, though, so it's an intermittent problem.

I had this trouble a couple years ago, and determined that a relay on the circuit board was bad, and replaced the board. It worked fine for two years, but now is having the same problem. When the igniter doesn't glow, I get a string of 4 blinks on the red LED on the circuit board. The 4 blinks means "open high temperature limit switch". Of course, this happens when the unit is ice cold, so there's no heat to open a limit switch.

I have found that tapping on the furnace in the general area of the purge fan occasionally improves my chances of getting heat.

Any suggestions?

[RHEEMXE80]

Update: Got out the multi meter & checked all the limit switches: one on either side of the burners, on in the chamber, and the vacuum operated one. All had zero resistance. Tested the vacuum activated switch, and it worked properly. Had resistance until the purge fan spooled up, then resistance went to zero. Even checked the high limit switch - it also had zero resistance. I pulled it out and gave it a visual inspection - it looks like new. No signs of corrosion, nice and shiny. Checked continuity all the way around the series circuit of limit switches - no resistance (when the purge fan is on). What's next?

[HayZee518]

if the limit switches are connected in series with the gas control and are supposed to be normally closed, jumper out each limit one at a time and see if the igniter comes on. the connections on the hot bar igniter could come loose. try re-crimping the connector on each lead. worse you might need a new igniter.

[RHEEMXE80]

if the limit switches are connected in series with the gas control and are supposed to be normally closed, jumper out each limit one at a time and see if the igniter comes on. the connections on the hot bar igniter could come loose. try re-crimping the connector on each lead. worse you might need a new igniter.

I've checked all the connections, but have not jumpered them. I'll try that next.

Also, is it possible for an igniter to be intermittent? It's such a simple circuit, it's just like a light bulb. I'd think it would be good till it fails, then be bad all the time. My problem is intermittent. Can that happen with an igniter?

[HayZee518]

I've had a hot bar igniter work then not work on my stove. I removed it and re-crimped the spade connectors. It worked sometimes, so I bought a new igniter [about 42 bucks] haven't had any problems in over 8 years. try that!

[RHEEMXE80]

Thanks Man

I installed a new igniter, part AF402. Cost $50. Measured resistance on the new one exactly the same as the old one. But, furnace fired right up. We'll know if the igniter was the problem after the furnace runs through a few more cycles calling for heat. Sure would be nice to be warm this weekend and to call the repairman and tell him not to come. (He can't come until Monday anyway.)

I don't know why a bad igniter would trigger a code for an open high temp limit switch. We'll see.

[RHEEMXE80]

Well, seems like no change. At some point in the process of bringing the house up to temp, the "upper limit" safety was triggered, and the gas shut off. All the limits switches are good. Purge fan is clean and blowing fine. It's making the vacuum it needs to make. All the limit switches test at zero resistance. All the connections have been checked. What's next?

[paul52446m]

Well, seems like no change. At some point in the process of bringing the house up to temp, the "upper limit" safety was triggered, and the gas shut off. All the limits switches are good. Purge fan is clean and blowing fine. It's making the vacuum it needs to make. All the limit switches test at zero resistance. All the connections have been checked. What's next?

You said you just bumped the area around the inducer fan and it would help.
Check the hoses for cracks around the pressure switch. check stack and intake pipe out side to make sure they are clear. Pressure switches can also react to
wind pressure outside. Check real close for lose wires on all controls., Paul

[RHEEMXE80]

Consistant open limit switch code

Thanks for your thoughts, Paul.

Well, had good heat on Christmas Day, but not so today. It's actually trying to start today, but switching off and giving the high limit open code. Strong wind outside could be messing with me.

I have noticed that this problem is much more frequent when it's coldest outside, which is also when the east wind is highest, as it is this morning. So, it's possible that outside wind is causing the open limit switch problem. I'm in a VERY windy area. I'll check the vent cap on the roof, too. Maybe it blew off in the big winds last night!

[RHEEMXE80]

Seems to be a Control Board problem

Okay, new discovery. It has nothing to do with wind. There's a bad solder joint on the control board. That's why tapping on things helped sometimes. Also probably why it was more likely to have problems when it was very cold out.

Where the main molex connector goes to the board, the wiring was a little tight, putting a slight sideways stress on the solder joints. Over time, the sideways pull on the connector, plus vibration from the furnace running, probably caused the break.

I'm getting a price on a board, but I'm going to attempt to re-solder that spot before spending more moolah.

[FooledMe2]

Similar issues w/ Rheem Classic 90 Plus

I had very similar issues, indicated by the an intermittent flame sensor signal (yellow LED on the control board). I could actually "modulate" the flame sensor indicator by tapping (sometimes emphatically) on the furnace housing. I called two different service techs, which relieved me of over $150 and left me essential where I started. The first tech declared that "most of these problems are just dirty flame sensors". He removed the sensor (which was indeed slightly discolored) , abraded it gently with emery cloth, and declared the problem solved - WRONG ! Later the same day, another tech came out & took measurements - pressure switch (OK) and flame sensor DC current (about 2 microamps, as I recall). He was suspicious of the control board - they typically do NOT do detailed troubleshooting & repair on the boards, they just replace them ($$$). I opted to not have him replace the board at that time.

After the furnace resumed its intermittency, i rechecked the electrical ground from the service panel to the furnace (was OK). I finally relented and bought & installed first a replacement flame sensor (symptoms remained) and then, reluctantly, a control board - the furnace ran OK for a day or two afterward, and the symptoms recurred. Several months later, I revisited the situation - it seemed to me that the internal "return" path of the miniscule flame sensor current must be involved.

I noticed that many of the hex-head sheet metal screws fastened into the same piece of metal (heat exchanger ?) to which the flame sensor is "grounded" were corroded. I removed one of these and found the serrated screw flange, as well as the head, to be corroded (the threads appeared OK). I re-tightened several more of these ugly screws, carefully removing the visible corrosion around & underneath the heads before re-installing each screw. I restarted the furnace, and over over the next couple of days, encountered no problems. This seems to be the most headway I was able to achieve.


I plan on replacing the screws with zinc-plated, serrated flange (vibration-resistant) sheet metal screws. I note that Trane advertises use of ceramic-coated screws in their models to inhibit corrosion. This may well be a design/materials issue on Rheem's part. I wish I had investigated the ground-path issue before splurging on a probably unnecessary control board.

[HayZee518]

corrosion

Zinc plated screws will develop an oxide coating over time. Call around a few places and see if you can get a can of a conductive grease.
I got a can of conductive copper [like never seize] and apply this to the screws before you torque them down. It might help also if you ran a ground wire within close proximity to the flamerod location to a know good ground on the unit.
this way you wouldn't have to depend on all the screws on the plenum, making its way back to the control board.