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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Janitrol M3UF044SA, it tries to fire up but after a

Customer Question

Customer: I have a Janitrol M3UF044SA, it tries to fire up but after a few seconds it just shuts down and never enights the flame. This has happened before and the guy I had fixed is not returning my calls... I think it's a sensor that controls the flame that has has gone bad
JA: Thanks. Can you give me any more details about your issue?
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Submitted: 11 months ago.
Category: HVAC
Expert:  Phil replied 11 months ago.

Hello,

So far it sounds like a bad igniter module, if you can locate that and unplug it, then check for voltage between the two sockets on the female side we can tell if its getting power and not glowing, in which case the igniter is bad, or if it is not getting power, in that case I need a diagram to continue with a diagnnosis.

Please attach a well focused, close up photo of the wiring diagram glued inside the service panel, the picture needs to be taken from straight on, in very good light.

You can use the paper clip- icon at the right end of the tool bar at the top of this dialog box to attach it here.,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If you have an error code showing, tell me what the code read out is on the wiring diagram or a sticker next to the diagram please.

If there is no paper clip-icon, look for the '+attachfiles'link at left of your send button.

I can mark it up with trouble shooting instructions.

We can go from there.

Customer: replied 11 months ago.
the igniter is good because it does start the flame, the flame stays lit for about 4 sec before it shuts down. So I swapped the two sensors from the other furnace and it stayed lit for about a minute, I put the other sensors into the other furnace that was working and it is still working fine.Maybe it's the blower that pushes the heat up into the house? Something is shutting down the flame so there must be other sensors causing this but so far not finding what one it is.See attached...
Expert:  Phil replied 11 months ago.

http://screencast.com/t/WZXIjjBHSw

I need a shot of the wiring diagram. That is a 10 x 12" sheet of paper glued to the inside of the furnace blower door in most cases.

Please attach a well focused, close up photo of the wiring diagram glued inside the service panel, the picture needs to be taken from straight on, in very good light.

You can use the paper clip- icon at the right end of the tool bar at the top of this dialog box to attach it here.,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

Customer: replied 11 months ago.
Please see attached as requested
Expert:  Phil replied 11 months ago.

Hello again, I saw what looks like a flame roll out switch, with only one wire attached, the picture is taken close up, I can't tell from that if it is a flame roll out switch or not.

In order to help you I need a picture of the wiring diagram.

Customer: replied 11 months ago.
I sent you the wiring diagram twice now, it's a good picture, can't you zoom into the picture so you can see the details better? Or what else can I take a picture of to send you???
Expert:  Phil replied 11 months ago.

No wiring diagram has arrived here so far...just two pictures of a limit switch...but no wiring diagram.

Customer: replied 11 months ago.
This pic: Sensor1.jpg I have the wires attached,just not it the photo. I actually removed the flame roll out switches from the good furnace and installed them in the bad furnace, it worked for a little while but after about a minute I had the same problem again. When I installed the roll out switches from the bad furnace into the good furnace the good furnace worked just fine all night.
Customer: replied 11 months ago.
How about these
Customer: replied 11 months ago.
Here are the same pics in low res, I hope they get threw to you this time
Expert:  Phil replied 11 months ago.

Thanks, ***** ***** wiring diagrams, in good enough light and well focused.

Expert:  Phil replied 11 months ago.

It will take me a few minutes to study them, and mark them up with trouble shooting instructions, 15 minutes maybe.

Expert:  Phil replied 11 months ago.

Clean the flame sensor rod, and its white ceramic base. If that fails you need a multi meter that has micro amps on it (uA)... then use that to measure the micro amp flow in the wire I marked in green, it should read 2 to 5 micro amps... if you have 2 to 5 micro amp current flow and the main gas valve does not open, then check for 24 volts at the gas valve. If you do not have 24 volts there, then the printed circuit board is bad.

Customer: replied 11 months ago.
I not sure you got what the problem is, it IS igniting the flame, the problem is the flame only stays lit for about 4-5 seconds and then the flame shuts down, everything shuts down. And the furnace tries this over and over, same result. So I think there is a sensor telling the furnace to shut down, I don't know what other sensors to look for???Thanks for your help!
Expert:  Phil replied 11 months ago.

I understand, it IS the flame sensor rod that I marked and asked you clean with steel wool that is shutting the burner off after 4 or 5 seconds however.

When that happens the printed circuit card will try 2 or 3 more times.

This will be the next set of tests that we do after you clean the flame sensor rod.

http://screencast.com/t/rZ2nFq61Guq

Expert:  Phil replied 11 months ago.

I mentioned this earlier, but here it is again

http://screencast.com/t/xTCHyValBwsg

The gas valve will not open if it is not getting 24 volts, that voltage has to pass through both flame rool out switches, you have one of them *disconnected*... that is at least one reason why the gas valve is not opening, there is no flame, the flame sensor rod then senses 'no flame'.. and it tries 3 times and then quits.

Customer: replied 11 months ago.
I told you it is not *disconnected* there is a flame! PLEASE READ WHAT I SAID IN THE LAST FEW MESSAGES
Customer: replied 11 months ago.
The ignitor IS igniting the flame, the problem is the flame only stays lit for about 4-5 seconds and then the flame shuts down, everything shuts down. And the furnace tries this over and over, same result. So I think there is a sensor telling the furnace to shut down, I don't know what other sensors to look for???
Expert:  Phil replied 11 months ago.

Hello again, you are basically correct, 100% correct most likely, it IS a Sensor that is shutting the furnace down.

Here is a mark up showing all of the sensors in the system

http://screencast.com/t/6CrT4O8JAik9

98% of the time it is a failure of the flame *sensor rod to detect flame, the other 2% of the time it is a bad printed circuit card, unable to read a valid flame *sensor signal.

First step is clean the flame Sensor rod.

Customer: replied 11 months ago.
Where is the flame sensor located?
What should I use to clean it with?Thank you!
Expert:  Phil replied 11 months ago.

The follow the wire I marked in green on the printed circuit card, it attaches to the back end of the flame sensor. unscrew the one or two screws there and remove the flame sensor rod.

http://screencast.com/t/UtEQc09ANPQE

The sensor will be found within an inch of one of the burners, with its long stainless steel rod poking into the flame area

Expert:  Phil replied 11 months ago.

there is no other item like it in the area.

Customer: replied 11 months ago.
Okay so how do you clean it
Expert:  Phil replied 11 months ago.

Use steel wool or Plumbers sand cloth.

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