View Full Version : Heater will not kick on unless...

October 19th, 2004, 12:46 PM
It's a Rheem Classic 90 Plus updraft unit, about 2 years old.

After a certain amount of time of not running, the heater will refuse to kick back on. Adjusting the setpoint or turning the heat OFF/ON also does not help.

By removing the lower panel (electronics, filter) then the upper panel (gas value, blower motor, intake, etc.), then replacing the lower panel allows the blower motor to start and eventually, the heater to ignite.

If you simply remove the lower panel and replace it, the blower motor will start, but that's all.

Any ideas?

October 19th, 2004, 05:55 PM
In the lower panel, you'll notice a little round "window" that peers onto the control board. When the unit shuts down, there will be a little light flashing in the little window. This will be flashing a code, seperated by a pause, and then the code again. Count the number of flashes, and correspond that number with the error chart listed on the inside of the lower door. Repost with what you find.

October 19th, 2004, 06:17 PM
2 flashes, then a 2 second pause = pressure switch is open

What do you think this means?


October 19th, 2004, 06:48 PM
I've posted a picture at the bottom of a typical pressure switch (not necessarily exactly line yours, but close). It is a saucer shaped control with a couple of wires and a small rubber hose connected to it. This pressure switch may or may not be the root cause of the problem, but it's error code does help us narrow the problem down significantly. When the furnace first calls for heat, the little combustion air blower first kicks on. This is the little blower that you hear. The pressure switch is what "proves" that the combustion blower is running. If you hear the little blower running (on the front of the firebox), then the pressure switch MAY be bad. First, check the white plastic flue pipe for obsuructions. Check outside and make sure that the bees havn't built a nest inside the end over the summer. If the end of the pipe appears open, check to make sure that you feel air blowing out of it (and sucking in the other pipe if there are two pipes). If this is okay so far, remove the little hose off the pressure switch. Blow through the hose and make sure that it's not clogged. Also, run a thin wire or other probe into little fitting where the pressure switch hose plugs onto the combustion chamber to make sure that this is not clogged. Most of the time this will solve your problem. If not, then we'll need to troubleshoot the actual pressure switch some more. Do this stuff and repost with where you're at.

October 20th, 2004, 09:10 PM
It looks like I have 2 pressure switches - one connecting to the firebox, and one connecting to the fan shroud. I checked both tubes and they were clear. The exhaust is clear as well as the intake. I also checked the nipple (fitting) where each tube connected to the heater. I used a paper clip to clear each nipple. There was nothing blocking each fitting that I could tell. I'm not sure if it was a coincidence, but after I cleared the fitting going to the firebox and replaced the tube, the fan started and the heater ignited.

But like I said before, after the heater runs through its cycle and stops often it will not start again when the thermostat calls for heat. Usually over a longer period of time, like overnight.

October 20th, 2004, 10:06 PM
Okay... now we're getting somewhere. On the left side of your furnace there are four punched holes. The top one is where the gas line comes in, the next one down is where the electric comes in, the next one down is for the thermostat wiring, and the one below all those is the condensate drain. Take all this condensate drain stuff apart and make absolutely sure that it's all free flowing. Heck, you can even pull it loose from the connection to the water collection box and run water out through the drain. A water backup (after a while of running) will cause the pressure switch to shut the unit off. Also, humor me, pull the hoses off the pressure switches again and manually (with your mouth) blow through the hoses back into the firebox and the fan housing and see that you can blow air through them in an unobstructed manner.

I'm usually not in a hurry to condem a pressure switch, since the problem is usually something else and the pressure switch error code is only the symptom.

October 28th, 2004, 10:16 AM
I've been watching it for several days now and it looks like it's fixed.

The last thing I did was disconnect several of the drain hoses. I also blew through the hoses going into the box. Shortly after I did this, the condensate pump kicked on as if more water had entered the pump. I guess there must haver been a clog somewhere?

October 28th, 2004, 05:55 PM
Whoo-hoo! Glad you solved your problem. I can't tell you how many furnace repairmen would have replaced that pressure switch and never solved your problem until they came back a couple of more times and discovered that clogged condensate hose.

October 28th, 2004, 06:57 PM
Thanks (again) for your help. You are really a wealth of knowledge!

December 27th, 2004, 08:38 PM
Look like it's acting up again...

The condensate line froze upon exit from the house last week. Needless to say, the heater stopped running which is how I figured out something was up. I rerouted the line so it dumps into my sump pump reservoir. Problem fixed...so I thought.

Ever since then, the heater has failed to start on call for heat 2 or 3 times. Every time I've checked the error readout and it's read "1 flash - 1 hour lockout". Not sure what that means, but after the first failure, I opened the doors checked the pressure switch hose again and all appeared fine. Upon door closure, the exhaust motor would run, the heater would try to ignite, but would not ignite, then it would go through the same cycle again, but the second time around the blower motor would start to run even though the heater had not ignited. I let it run for a little bit and then opened the doors again. I rechecked the pressure switch and closed the doors. It started up.

A little while later it failed with the pressure switch error (as in my first post). I checked the switch again and it appeared to have some water in the switch. I removed the switch, patted it against my hand to try and remove the water. It appeared I got it all out, so I reassembled and the heater started up fine.

A couple of days later I noticed the same problem with the same error "1 hour lockout". I tried removing the doors and replacing them and it started up.

Today I came home from work to find the same problem. I removed the doors, replaced the doors and it would fail to ignite as the first time... removed the doors, check the switch (dry) and replace the doors. It started up.

Any idea what might be going on? Any idea what the "1 hour lockout" error code means?

Thanks for any assistance!

December 27th, 2004, 09:33 PM
The one hour lockout is a nice feature on some models of gas furnaces. For natural gas furnaces, the spark starts and the gas valve opens. If the unit tries this 3 times without sensing a flame, it goes into a one hour lockout and tries again. This one hour lockout gives any gas fumes time to waft out of the furnace. On LP gas furnaces, the spark starts and the gas valve opens. The unit will only try this one time on an LP gas furnace, and go into a one hour lockout and try again. You probably need to clean the flame sensor with a little steel wool or fine emory cloth. It's a thin metal rod probe sticking into the flame with a single wire attached to it. Normally, the sensor is only held in with one screw. The probe may visually look clean, but a strange oxide layer builds up on it preventing proper flame sensing. This should fix you up this time around.

December 27th, 2004, 09:46 PM
Cool. I will take a look at it tomorrow. Thanks again.

Why would you think it would not ignite when I tried to restart it? I would think if I could force it to restart by remove/reinstalling the panels AND the heater had no problem with the ignition, it would ignite.

December 27th, 2004, 09:53 PM
These flame probes are funny that way. They'll work intermittantly before they quit all together. Buffing them up with a little steel wool (5 minute job) is a good annual PM thing to do. When you remove the doors of the furnace, the power switch pops out and then gets pressed back in when you replace the doors. This circumvents the 1 hour soft lockout.

March 8th, 2005, 06:14 PM
I cleaned the probe after more recent shutdowns. Still having problems. Giving me the error "pressure switch open" again. I took another look at the pressure switches. Looks like the switch connected to the inducer motor is bad:

-When I remove the hose from the motor end and blow back into the switch, it sounds as if air is leaking somewhere within the switch.

-Try the same thing with the switch connected to the box and I am unable to blow through the hose, ie. the switch is not leaking air.

-I left the hose disconnected from the inducer motor and powered on the furnace. Immediately the furnace showed the same error.

Does this sounds like a bad switch to you?

Calling Rheem tomorrow for a replacement...

One more question....does Rheem need anything else besides the model # and s/n of the furnace to provide me the proper pressure switch?

March 8th, 2005, 09:55 PM
Trying to follow this post best I can. Not sure about this pressure switch error code but that flame sensor is usually dependent on the burner directly related to it...igniting....at least thats how mine works. So lets say that burner isnt igniting but the others are igniting. The sensor could not prove flame if "its" burner is flameless and the furnace will shut down. Just an idea.

March 8th, 2005, 11:00 PM
Model and serial is all you need for a replacement pressure switch. A "leaking" pressure switch is undoubtedly bad.

March 9th, 2005, 09:33 AM
Turns out the number is 479-648-4900 for furnace customer service... and they won't send me the parts. They said I have to go through a distributor and they won't even sell me the parts. Which means I have to call someone to come out and service it. Total BS. Why won't they just give me the part and I can install it. It would take all of 30 seconds to install.

What gives? Can anyone help me out?

March 9th, 2005, 05:39 PM
Check online. Places like furnaceparts.com is one online retailer.

March 10th, 2005, 03:05 PM
Finally found a local guy that would sell me the part. Prior to installation, I tested the new switch (looks different) with my "blow through the hose" test. The new one leaks, too!!!

I looked at the new switch and at the base of the hose nipple there is a tiny hole that is allowing air to escape. Then I took a look at the old switch...it too has a tiny hole, but on the old switch you can cover up the hole by inserting the hose all the way on the nipple. It was not covered up before, hence the air leak.

Right now I have the old switch on the furnace with the hole covered up to see how it operates.

What is this hole for? Should it be covered up?

Sorry for all these questions...hopefully they might help others with the same situation.

March 18th, 2008, 09:05 PM
Not sure if too many people check this thread, its been awhile since any new posts. But let me give a big THANK YOU to all who posted here especially "mdshunk" my Rheem Classic 90 was having some serious issues: lots of clicking before it would light, shut off and the blower would continue blowing cold air, after a couple days of thinking it was the remote sensor and fiddling with it, i noticed a drop of water, anyway cleaned out the hoses and everything seems fine. Thanks for the help

January 20th, 2010, 05:15 PM
Wow - with the help of the info in this thread, as well as some others, I was able to get my Rheem Classic 90 back online this past Saturday night, and avoid having to pay for a service call on golden time...

In a nutshell, I noticed the furnace kept trying to come on (draft inducer would initiate), but the burners would never fire, and the circulation fan wouldn't come on.

First thing I did was make sure the air intake and exhaust lines were free of ice and snow - check.

Next thing I tried was to clean the flame sensor with emory cloth - problem remained..

Then, using a syringe, I drained all the water out of the drain trap - problem remained.

Finally, around 10pm, on a cold Ontario winter night, I called the 24hr emergency line to log a service call. With 3 kids aged 4 and under, what else could I do?? I left my name and number, and waited for a return phone call... While I was waiting, I came across this thread. I read MDSHUNK's message about the pressure sensors, and figured I might as well give it a whirl while I waited. Guess what?? PROBLEM SOLVED!!!

I immediately called the furnace guy, and told them not to bother coming by, and my wife and I settled in to a nice warm cozy bed in a nice cozy house.

Thanks to everyone for their help, and for saving me a really expensive service call!


November 5th, 2011, 05:06 PM
The Q's and A's really helped. I have the 90 classic plus which was having the exact same problems. I had checked the hoses and everything else and I thought I had a bad pressure switch. After reading this thread, I realised I hadn't cleared the nipples with a paper clip. Great tip. Turns out something (very small) was partially blocking airflow into the small fan in the front of the main blower. Probably would have lost time and or money if not for your help. Thanks again:beer:

October 19th, 2013, 11:58 AM
I've followed all the very helpful suggestions and I now have the furnace warming up the house... But it only works if the top panel is off.

I pulled and sanded clean the flame sensors, cleared the drain lines, checked rubber vacuum tubes and nipples with a paper clip, but it still wasn't even starting a flame.
To see what was going on and why it wouldn't even try to flame up, I held the bottom door sensor in while it went through a cycle. For the first time I got flame. I attached the top panel and was trying to figure out how I would get the bottom on without releasing the button when the flame went out. Like its lost its oxygen supply. Of course, when the flame went out the cycle went back to a pressure switch signal.

It works fine with the top panel open. I'm warning the house now and then I'll reassemble the doors as I recognize I can't just leave it off. Anyone know if there is an air intake somewhere that I can check for an obstruction?

March 21st, 2014, 11:25 PM
I just want to say thanks! Great thread, Great info. mdshunk gave great help. I too have had some problems with this heater. Mine is probably 10 years old. I just bought the house last fall, and am pretty sure it is original from when it was built. My issues and solutions were:

Problem 1: This winter in -25 degree weather the heater stopped working. The thermostat would call for heat. The combustion blower would kick on, 10-15 seconds later the spark would come, and the flames would start. They would blow for a while, and then the fan would come on to blow the air throughout the home. All would be working just as it should, however, after a few minutes the flames would stop and I would get the pressure switch signal. After much trial and error I found that it would stay working as long as I had the upper door off, and was staring at it. As much as I would like to believe I just have a very intimidating stare, and that it worked out of fear, as soon as I put the door back on it would stop. I then discovered there are two black plugs on the right side of the upper part of the furnace, that if popped out, the flames would stay lit. This led me to believe that it must be an air flow issue. I traced the problem back out to the outtake pipes outside and found when installed one was inside of the other. I also found that there was a cap placed in front of them to keep birds from nesting in them. The cap was designed to allow proper air flow to both pipes, but I removed it just for kicks and giggles to see what would happen. Fixed the problem.

Problem 2: We woke up to find that the furnace was once again not working. This time, however, there wasn't even a call for spark. the blower would start, run, then shut off. The green light code was pressure switch again. I first checked the pipes to make sure nothing had clogged them. not the problem, then by supreme intervention I found this thread. I followed mdshunks advice, and found that the pressure switch was working. If I sucked on the hose, then the heater would work. I even held it open with a screw driver for five minutes to ensure it would continue to work. But when hooked back up to the blower it would not open. I then used a copper wire though the attachment hole on the blower, and could feel something lodged in it. hooked the pressure switch hose back up, and it opened just like it should. Now my family is warming up and basking in all the heaters glory. Don't realize how much you love having a heater here in Minnesota until it is gone.

Again, thanks, and I hope someone can get something from my addition.

February 18th, 2015, 02:55 PM
I -THINK- this has also solved my problem too. Ever since using a toothpick to clean out the exhaust blower and pressure sensor nipples where the rubber hose goes, and being sure the exhaust has no water in it, the thing's been cranking, knock on wood. (As soon as I hit enter, Murphy's law will take over.)