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Old 02-10-2019, 11:23 PM   #1
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Help to troubleshoot intermittent furnace issue

Hi Folks,
Simply put, the furnace just stops heating. All I need to do is turn it off, turn it back on, and all is well..... until it isn't. maybe a few hours, maybe a day. We've not had a problem with the heater prior to this.

So it's finally getting cold here in WA. We use the RV so it's not winterized, It's plugged in, water heater on, and furnace on, cabinets open etc.. all has been fine until these past few days of extreme cold. Not sure if this is coincidence, but for the first time in a long time temps are dropping into the 20's. We've never had an issue with the heater before. I have a remote thermometer in the house to keep an "eye" on things in the RV and the past couple of days, the furnace at some point stops heating.

Like I just did, as it was down to 46 inside the RV, I ran out, turned the system off at the thermostat. Went over and lit the stove just to be sure there was plenty of gas at a decent pressure. All was fine. Turned thermostat back on.... the normal short pause... fan comes on... 15 seconds later a click (the ignitor), and we have heat.

I went through every troubleshooting guide I could find. I can't really tell if the fan runs continuously after it stops heating. I know once it gets up to temp it cycles down as it should, but a couple of times when I've gone out when it hasn't been heating anymore, the fan was running. However, once it wasn't so I don't know if it's a timing thing on my part.

Any thoughts from the IRV2 hive mind on this? I'm thinking that somehow maybe it's over-heating cause the safety to kick in, but then I'm not sure why it's not restarting once it's cooled unless that is a safety feature as well. I'm not really sure how it would be overheating either, I'm just grasping at straws because as I said... if I just turn the system off and back on... it starts working just fine.
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Old 02-11-2019, 12:07 AM   #2
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I have had a similar problem. In my case it was plugged return vents which caused the furnace to turn off on high temp. Cleared the block in the return vent and the problem went away. This can also happen if a bird or bugs build a nest in the exhaust pipe or all the hot air vents are blocked.. If the furnace turns off on high temp. It will run the fan until it cools down then it will not restart until the power is cycled. Hope this helps.
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Old 02-11-2019, 12:15 AM   #3
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If the furnace turns off on high temp. It will run the fan until it cools down then it will not restart until the power is cycled. Hope this helps.
Hmmm.. I will check the vents in detail although I periodically put my hand over the exhaust to feel if heat is coming out, and can feel the suction of the return, but I haven't actually looked in with light since this nonsense started.

However, it would appear the "high temp" is the reason it's shutting down based on how I have to just cycle the power to restart. I wonder if the over-temp sensor is going bad and triggering too soon.
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Old 02-11-2019, 12:35 AM   #4
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Yes, if the high temp switch gets activated several times it will fail and could trigger too soon. I had that problem as well. My original problem was caused by a manufacturing defect. I assume yours worked at one time. If not look to see if the return path through the floor is blocked like mine was. During manufacture someone noticed they could save about 50 ft of electrical wire if they swapped the electrical panel under the stove with the return vent under the refrigerator. It was a great move, but they never cut an opening between the two spaces. This blocked the furnace return vent and caused the problem. Took me months to figure it out and even then it was by accident.

On a suburban furnace the high temp switch is on the back top. You must remove the furnace to get to it.

Hope you find your problem soon.
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Old 02-11-2019, 12:55 AM   #5
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Originally Posted by APhotoWizard View Post
Yes, if the high temp switch gets activated several times it will fail and could trigger too soon. I had that problem as well. My original problem was caused by a manufacturing defect. I assume yours worked at one time. If not look to see if the return path through the floor is blocked like mine was. During manufacture someone noticed they could save about 50 ft of electrical wire if they swapped the electrical panel under the stove with the return vent under the refrigerator. It was a great move, but they never cut an opening between the two spaces. This blocked the furnace return vent and caused the problem. Took me months to figure it out and even then it was by accident.

On a suburban furnace, the high temp switch is on the back top. You must remove the furnace to get to it.

Hope you find your problem soon.
Thanks... I'm going to order the sensor. On this model, it's actually on the front. The "return" is the entire top rear of the furnace and yes it was working fine up until about a week ago when it started getting really cold.

I actually had the unit out about a month ago just to check it out as I assumed maintenance was never done. The whole unit looked pretty unused inside and out so I just cleaned, adjusted and reinstalled. And yes, it worked fine after I had it out too. It's ok... I was thinking that too.

I'm pretty sure it's the high-temp sensor at this point. You guys pretty much confirmed my suspicion.
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Old 02-18-2019, 01:00 AM   #6
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So the plot thickens. I'm hoping someone can review this and I'm open to any other possibilities.

The intermittent problem was not the limit switch after all. Today I got really intimate with the Furnace and it turns out Gas isn't getting into the chamber. Now I'm thinking I need to replace the valve, but... I'm not positive because the valve still "works". By "works" I mean I pulled the valve out and using air and a 12v source triggered the solenoids and blew air through the line and it went all the way through. I also tested the tubes on both sides and there is flow all the way into the chamber.

There is plenty of ignitor spark, but I don't even smell the slightest amount of gas while it's attempting to ignite... and based on everything I have done, there should be something.

To be clear before I got the point of pulling the valve I tested all the normal culprits and everything seems to be working just fine. The ignitor spark is a nice blue spark. But with the furnace out of it's case, as it's going through the three spark sequence, I should get some faint hint of propane gas smell, and I'm not. As I said, the individual components seem to work, and I can get air all the way through the line, through the valve into the chamber... the ignitor works, just no ignition. FWIW, I was also testing with a separate tank and regulator when attempting to use actual propane and not air.

I'm looking for any input as far as agreement on the replacement valve? The reason I'm hesitant is after I decided it was the valve, I took the valve apart. It seemed like one side, the little puck with the spring on top, was sticking. So I unstuck it. I thought I solved the problem, put everything back together, re-tested for flow, was sure I fixed the furnace... but it doesn't lite and there is still no smell of gas during the lighting cycle. So I want to say it's the valve, but the valve seems to work fine. I just can't test the actual amount/rate of flow. There was no sludge or anything in the valve.

Am I missing something? Could maybe a needle or port be worn enough to allow gas, but not enough gas to pass? Has anyone else had such an issue?
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Old 02-18-2019, 05:06 AM   #7
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Sounds like your lp regulator might be freezing up at night.
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Old 02-18-2019, 12:41 PM   #8
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Sounds like your lp regulator might be freezing up at night.
That was my original thought, but my testing is with a different regulator on my workbench.
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Old 02-19-2019, 04:51 AM   #9
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You need to check for voltage at the solnoids on the LP valves. If 12 volts is there then check the ohms on the solenoids. Voltage not there then replace the board. Ohms to low on ether side replace the valve. Be careful if you take them apart (lp valve) and don’t put it back right they will explode.
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Old 02-19-2019, 06:10 AM   #10
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I am having a similar if not the same exact problem. (See my post). It is completely intermittent! For instance in November the furnace stopped working at about 19°F, woke up cold when the inside temp hit 35° last night I let it run here at the house because I'm trying to diagnose it, it got down to 3°F....went out to the rig this morning and it's 75° inside!

We have replaced, both tanks, both lines from tank to regulator, regulator/change over, entire furnace...yes you read that correct...we replaced the old 8525-II, with a new 8525-IV and continue to have the same problem!

The only things we have not replaced is the thermostat and the hard line under the rig. I'm working on trying to retrofit a digital thermostat now.
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Old 02-20-2019, 12:49 AM   #11
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You need to check for voltage at the solnoids on the LP valves. If 12 volts is there then check the ohms on the solenoids. Voltage not there then replace the board. Ohms to low on ether side replace the valve. Be careful if you take them apart (lp valve) and don’t put it back right they will explode.

As stated above, the LP valve seems to be working fine, but I ordered a replacement anyway as it's the only part stopping gas from getting into the chamber. The tube is clear, sail and sensor are getting voltage and acting normal...

By working, I mean the board sends 12volts, and it trips it open and on the bench when it trips open I can push air through.
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Old 02-20-2019, 04:17 AM   #12
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As stated above, the LP valve seems to be working fine, but I ordered a replacement anyway as it's the only part stopping gas from getting into the chamber. The tube is clear, sail and sensor are getting voltage and acting normal...

By working, I mean the board sends 12volts, and it trips it open and on the bench when it trips open I can push air through.
Is there 12 volts on the LP Valve continuously? or is that dropping out?
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Old 02-20-2019, 04:22 AM   #13
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Originally Posted by jduffey5 View Post
I am having a similar if not the same exact problem. (See my post). It is completely intermittent! For instance in November the furnace stopped working at about 19°F, woke up cold when the inside temp hit 35° last night I let it run here at the house because I'm trying to diagnose it, it got down to 3°F....went out to the rig this morning and it's 75° inside!

We have replaced, both tanks, both lines from tank to regulator, regulator/change over, entire furnace...yes you read that correct...we replaced the old 8525-II, with a new 8525-IV and continue to have the same problem!

The only things we have not replaced is the thermostat and the hard line under the rig. I'm working on trying to retrofit a digital thermostat now.



Classic case where you should have called someone that knows what they are doing. You've spent all that money and it is still not fixed. It is ether a $40 dollar t/stat or a relay in the AC $89. easy to find. You start at A testing not at Z.
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Old 02-20-2019, 02:22 PM   #14
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Is there 12 volts on the LP Valve continuously? or is that dropping out?
THAT is a good question. I was sure I tested that and initially posted that it stays at 12v, but just hooked everything up, and it ONLY stays at 12V for a few seconds each time the ignitor engages.

What should give it the signal that ignition has occured and it should continue to keep the valve open?
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