Propane heater fan won't stop running


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Old 10-24-16, 04:31 AM
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Propane heater fan won't stop running

Hello everyone. I've got a problem with my older, modular home heater. This heater uses propane fuel. A few days ago, I noticed the heater fan was running, but cold air was coming out of the registers. Normally, the fan runs about 3 to 5 minutes after the temperature in the room reaches the set degrees on the thermostat, and the thermostat tells the heat to shut off. I think that is a safety feature. First thing I did was turn the thermostat down to it's lowest setting to see if the fan would turn off. It didn't. I then checked to see if the fire in the firebox was out, and it was, but the pilot light was still burning and the fan was still running. As there is a fan switch at the heater itself, I then shut it off manually. This is when I started getting nervous.
Since this heater was designed to use propane normally, when you turn up the thermostat, a "pre-ignition fan" turns on for about a minute. I believe this is a safety feature to remove any accumulation of propane should there be a leak. But I'm no expert. And this is why I'm hesitant to do any tests yet. Although, I did do one test.

I turned up the thermostat, but the fire in the firebox did NOT come on. Nor did this "pre-ignition fan". So, at the risk of an explosion, I then manually turned the furnace fan on. At this point, the fire in the firebox came on as well as the furnace fan. I immediately felt warm air come out the registers.

At that point, I went online to youtube, and viewed every video regarding "heater fan won't shut off". They were helpful, showing the various things that could cause this. Unfortunately, none of the videos delt with PROPANE heaters, nor any info about that "pre ingnition fan" or dangers associated should it not come on.

As for the thermostat, this is the original, Honeywell with a mercury switch, but no other switches, like auto, on/off etc. I understand the various tests shown in the videos, and am fairly competent using a multimeter etc. But, for the reason mentioned above, I felt it behooves me to ask for any other advice regarding any dangers per this "pre-ignition fan". I haven't began visual inspection of the thermostat wires nor any tests yet but I will upon your approval to start. So... that's the problem. Any advice would be appreciated, as the temperature outside dropped to 30 degrees last night. And my wife doesn't like being cold. Hence...I gotta get this thing fixed...pronto. Hahahaha..
 
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Old 10-24-16, 04:36 AM
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Holy moly. I left the heater running when I did that test, which was 5 minutes before I sat down and posted this thread. I just noticed. The fan has STOPPED and the heater shut down when it reached the set temp on the thermostat. I'll wait to see if it comes on as soon as it cools down inside the house. This suggests some kind of intermittent problem with maybe a relay? I'll let you know as soon as it comes on again. IF..it comes on.
 
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Old 10-24-16, 05:33 AM
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Oh for cryin out loud. Getting old sucks. My memory is a fail. I must have turned the fan switch off. It didn't turn off normally. Please excuse my numb skull. Carry on. Same problem remains.

What a moron.
 
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Old 10-24-16, 10:59 AM
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What you call the pre ignition fan is properly called the inducer motor and fan.

The purpose of these parts is to circulate combustion air into the furnace for combustion and then out of the furnace and into the vent to get rid of the combustion products.

Both propane and natural gas furnaces have inducer motors these days.

Your description of what is happening is hard to follow.

Take the cover off the furnace and follow the SEQUENCE of events that occur when the thermostat is turned up. Describe that sequence of events here in order and in detail.

Furnaces don;t just turn on. They follow a sequence of events that produces heat if the sequence is followed all the way. If it stops short, it help identify likely problems is the furnace may have.
 
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Old 10-24-16, 12:36 PM
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Is the unit calling for heat? Do you have and know how to use a meter?
 
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Old 10-27-16, 07:36 AM
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Sorry for the delay getting back here. Too many things to get ready for winter. As it is..it caught me off guard yesterday. It snowed all day. Gak!!

Your description of what is happening is hard to follow.
Gads, ok. I'll try to make it simple. In essence, when I discovered the fan was running, but blowing cold air, I went to the thermostat and checked the setting. I then turned the thermostat down to it's lowest setting. NORMALLY, if I turn the temp down, or the house temp reaches the temperature set on the thermostat, the fire in the heater shuts off, but the fan keeps running for a few minutes. In this case, it just kept running, till I shut it off manually using the fan switch in the heater.

Now, if I turn that switch on, the fan starts running, as well as the fuel ignites immediately and warms the house up to the thermostat setting, at which time, the heat shuts off but the fan keeps running, just as I described. However, I can't tell when the fire shuts off, so if the house is warm, I shut off the fan manually.

Take the cover off the furnace and follow the SEQUENCE of events that occur when the thermostat is turned up. Describe that sequence of events here in order and in detail.
Ok, if the fan is turned off, nothing happens when I turn the thermostat up.
If I turn on the fan, and THEN turn up the thermostat...the fire kicks in. But if I turn the thermostat down, the fire turns off, but the blower fan keeps running until I turn it off manually. However, at no time do I hear that "inducer motor" come on, as NORMALLY, it comes on FIRST when I turn the thermostat up. After a few minutes, the regular fan starts blowing warm air. However, if this so called "inducer fan" runs all the time the regular fan is running, I can't hear it as the blower fan is much louder.


That's the best I can describe. There is NO sequence. Either the fan is on..or it isn't. Like I said..NORMALLY the sequence is..

Turn up the thermostat.
Inducer fan starts
Fuel ignites in fire box
a few minutes later, the blower fan starts.

But not now.

Ok guys, that's what's happening. Btw, I know how to use a multi meter.

For what it's worth, the manufacturer is Miller. However, I can't find a model number anywhere, but here is some pics. I finally opened a panel secured with two screws. Inside, there are some transformers, what looks like a couple of sensors, and wires leading to various places.
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Also, I'm used to fixing things and trouble shooting. In this case, I just need some insight into narrowing down the possible cause. However, from the videos, it appears there's about 4.
Thermostat.
Thermostat wires shorting
Open wires
Sensors.

Unfortunately, I don't have a schematic and don't know which item is the correct sensor, as it appears there are two in that panel.

Now what?

Oh, FWIW, the other day, just prior to discovering the fan running, I heard what i think was a cat in the ductwork. Last year, I had one of the registers off to fix the duct connection. While it was off, one of my wifes cat's, climbed down in that duct, and we couldn't get it out for 2 hours. Finally, we saw the cat outside. My son climbed under the house and found a place where somehow, the cat had disconnected one of the ducts. Don't ask me how. My son fixed that connection, but somehow, a cat tried to get back up in the duct as these are wild cats and they climb up around the insulation around the ducts during winter. I'm guessing they might have broke, or shorted one of the thermostat wires. What I don't understand is how to test for it. Any info would be appreciated.
 
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Old 10-27-16, 07:43 AM
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Is the unit calling for heat?
Hello roughneck77. I don't understand the question. Which unit?
And how does it "call for heat"?

Are you referring to the "thermostat" telling the heater to turn on?

If so, then yeah. I turn up the thermostat to call for heat.

Unfortunately...unless I manually turn the blower fan on.. the heater doesn't listen.
 
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Old 10-27-16, 08:05 AM
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Ok guys. I got down and visually inspected everything in that panel. I identified the two thermostat wires. One tan, one red.
In the panel, there is a transformer, and some kind of what appears to be a relay, although I'm not certain. Up in the upper right corner, there is what I think is a large "thermocouple" or maybe some kind of sensor, and to the left of it, a small sensor of some kind. There are a bunch of wire connections, all of which appear to be good, and I saw no loose or disconnected wires. Right above this panel, right beside the blower, and mounted on the firebox, is another small sensor of some kind, that appears to be connected to the inducer fan motor, although other wires are also connected to other things.
Also, there is a note about replacing a "thermocouple". But it says that one is down on the gas controller, and only hand tighten it.

I've also opened the thermostat, which is an old mercury switch design. If I turn the blower fan on, and THEN turn up the thermostat, the fuel ignites, which tells me the thermostat must be good. No? What i DON'T understand is, in the videos, all the units had a green wire from the thermostat too. But those were the newer digital type thermostats.

Anyway, that's all I can tell you at the moment. If you can tell me how to test or what to test, I'll do it. My multi meter is just an old analog meter, but works for me. Mostly for continuity checks and testing for household AC. Ok guys...I'm all ears.
 
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Old 10-27-16, 08:27 AM
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Hi guys. Well, I did some more online investigation and found a site for Miller heaters. It had a section on my problem. It suggests:

"If the blower does not shut off, shuts off too soon, or not soon enough because it blows cold air at the end of the heating cycle, then the problem is most likely a bad temperature control switch."

Ok, sounds like I should test mine. Unfortunately...I don't know which component is the "temperature control switch". Nor how to test it. Can someone point it out for me and tell me how to test it? At least this will eliminate on possible cause. Thanks
 
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Old 10-27-16, 10:34 AM
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When you say you manually turn off fan, I'm thinking you open the switch on the wall? Which means you turn off power to the furnace. Am I correct or reading something into this that doesn't exist.
 
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Old 10-27-16, 10:44 AM
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hi mbk3. Like I said at the very first post, there is a blower fan rocker switch, right on top of that panel box where all the sensors/transformers etc are. You can barely see it in the close-up pic of that box. It's on the left end of the top, just past those wires that enter the box at the middle.
 
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Old 10-27-16, 10:51 AM
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Sorry I missed that. Post was very long. Ok, looks like that is power disconnect, not a manual fan switch.
 
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Old 10-27-16, 10:54 AM
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Look at the thermostat disc type switches on the face of the furnace. Try and find the one with an F in the number. Like F-140 and give it a tap with a screwdriver handle.
 
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Old 10-27-16, 12:23 PM
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Ok, looks like that is power disconnect, not a manual fan switch.
Oh, it didn't dawn on me. Ok, it works the same though.

As far as those "thermostat disc type switches", are those the ones that look like a "transistor", or a sensor of some kind? They look similar to some I've replaced in dryers. No matter, I'll tap all of them. Thanks... btw, out of curiosity, which one would be the "temperature control switch"?
 
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Old 10-27-16, 12:35 PM
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Try and find the one with an F in the number. Like F-140 and give it a tap with a screwdriver handle.
Ok, I found it. F115-something. Turned the thermostat to lowest setting. With the power switch set to OFF, I tapped on it and then turned the power switch ON. The fan came ON. Apparently, this didn't work. Is there a test for it?
 
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Old 10-27-16, 01:31 PM
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Yes there is, is it a two wire switch. If yes pull one wire off and blower should stop.
 
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Old 10-27-16, 05:34 PM
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My gas furnace has a high limit/ fan control sensor that is located in the exhaust portion of the furnace. The sensor rotates in 1 direction for a heat rise and in the other direction for a heat fall. There are two switches mounted on the fixed portion of the sensor. One switch is used to shut the furnace off on a high limit temperature. The other switch is used to turn the blower (fan) motor off after the thermostat has been satisfied and the sensor has rotated in the heat fall direction to operate the switch that opens the circuit to the fan motor.
Being a mechanical device, the fan control can build up friction which affects rotation. Sometimes just tapping the device will free it up. Some sensors have adjustable setpoints. I would not touch these unless you have the manufacturers operation sheet as there are restrictions between setpoint adjustments that must be followed for the sensor to operate properly. Hope this helps.
 
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Old 10-27-16, 07:09 PM
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Yes there is, is it a two wire switch. If yes pull one wire off and blower should stop.
Well, it's a two TERMINAL switch. With one terminal connected to ONE wire, and the other to TWO wires. Should work the same. I pulled the wire at the single wire terminal off. Nothing happened. The blower fan kept running. Now what?
 
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Old 10-27-16, 08:45 PM
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Those furnaces are made by several different companies. It says Miller. It could be part Coleman or Nordyne. I see a two terminal limit switch in your picture. I'm guessing that's the one that has three wires and you tried disconnecting the single one.

I found a very similar model to yours but it's apparently slightly newer since it uses a control board.
Nordyne Furnace Model M1MB 077A AW (M1MB077AAW)Repair Clinic

The wiring diagram would have likely been on the back of the cover for the control area there.

I can help you with your wiring but I need BIG pictures. Much larger than could be posted here. I see a relay there but I can't see enough definition in the wiring to see how it's connected. If you have the ability to take large pictures.... you could send them directly to me for hosting or host them yourself. http://www.doityourself.com/forum/el...-pictures.html
 
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Old 10-28-16, 04:35 AM
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Hi pjMax. Thanks for chiming in. Well, there is some various labels on the inside of the furnace, and one of them has the term Nordyne on it. The main cover of the furnace has a Miller label on it.
Ok, as far as large pics are concerned, I just opened a Photobucket account and uploaded that closeup pic of the panel box. If this doesn't look big enough, I'll take another pic and upload it. Here is the link...

http://i1249.photobucket.com/albums/...psni0mctjy.jpg

As for the switch, you are correct. It's in the upper right corner of that box. How would I test this? I mean, it's just a switch, but how do you find out if it's supposed to be open, or closed...and when? In the meantime, I'll look at that cover and see if there is a schematic. Anyway, I need to fix this. It's getting really cold now, and I haven't got the funds to call a pro. Thanks for the help. I really appreciate it.
 
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Old 10-28-16, 09:49 AM
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Wouldn't open for me for some reason
 
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Old 10-28-16, 09:53 AM
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photobucket is temporarily having problems.
 
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Old 10-29-16, 02:26 AM
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The picture opened for me this morning. Took about half a minute though.
 
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Old 10-31-16, 10:06 AM
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Ok, photobucket is working again. (hint hint)
 
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Old 11-14-16, 08:34 AM
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Oh....my.....god.

Hi everyone. Sorry it took so long to get back. Too many winter projects to fix. Finally got back to this.

OMG. Problem FIXED!! In fact, all I had to do was look at the schematic. I was just taking a picture of it to post here, when all of a sudden..I noticed something. There was a symbol, for the rocker switch I've been using to turn the heater off/on. However, right below the outline of this panel that encloses all the wiring, there was ANOTHER symbol. This one was labled Auto/Fan ON. BINGO!! I went and looked. Sure enough, there was another switch, mounted right on the flange for the cover. I'd never noticed this switch before. It had somehow been switched to FAN ON. DOH!!! Haven't got a clue how, other than I may have accidentally switched it when the last time I was laying on the floor lighting the pilot. OH WELL. Fixed. Now I know.

Anyway, I just wanted to thank everyone for their help. If you hadn't told me to look for the schematic on the back of the panel cover...I'd never known. THANK YOU.

Ok..now for Project #37 on the list of 82 things to do.

Arrrrrrrrrrrgggggggggggrrrrrrrrrr!
 
 

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