Hi,
I have Nordyne downflow gas furnace FG6RK series

Here's sequence and symptoms
- Inducer motor turn on fine
- Then HSI turns on.. then gas.. also all three burners turn on.. flame sensor recognizes flame
- Few seconds later main fan turns on fine..and i get hot air.
- There are two LED's RED and YELLOW... Both statys solid as it should be (according to troubleshooting lable)

However.. after 2-3 minute of HOT air..
- i hear one click.. then after 5-10 seconds i hear 3 to 4 back to back clicking sound and after 5+ seconds gas turns off.
- I monitored RED and YELLOW LEDS during that clicking time and in summary neither of them shows any blinking.. basically RED statys solid and YELLOW turns OFF when gas turns off.

I originally thought may be flame sensor even through YELLOW did not blink to show its flame sensor not recognizing flame .. So i replace flame sensor.

I also have new filter.. all ducts/vendors are very clean.

When furnace turns off unexpectedly.. i go to thermostage to verify and it is sending 'system on' status.. meaning furnace should be ON.

But problem continues and repeats.. appreciate any help or suggestions i can get.

Thanks.

 

Welcome to the forums!! Based on your observations, it does sound like a flame sensor issue. You stated you replaced the flame sensor and the issue continued. Are you sure you positioned the flame sensor properly when replacing it? It might only require a slight adjustment to ensure proper flame impingement.

Here is a link to the installation manual for your furnace:

http://enora.nordyne.com/Literature/708291b.pdf

 

yeah, i did position flame sensor and its right in middle of last flame.

If not then i was thinking it would blink YELLOW light and normally it wouldnt even give hot air for few minute.

 

The control board should be indicating a flash code when the furnace shuts down. Have you bypassed the thermostat to eliminate that as the cause of the problem? I suggest you place a jumper between R and W terminals at the furnace control board to see if the furnace starts up and operates properly without the thermostat in play.

 

Control board did not indicate any flashing led to report problem.

I will try bypass thermostat...when jumping R and W, should i leave thermostat connected? Or just remove batteries?

 

Alright i disconnected battery from thermostat and connected R and W, system came on with hot air for few minutes and then shuts off with same symptoms. Again no trouble codes from leds, Red solid on all time and YELLOW solid on when flame present.

Something to add in symptoms (before R to W connection), after unexpected stop system trys to start again and after 3-4 retry like this system does stop normally meaning when it hits right temperature.

 

Remove the filter & try running the furnace. If the furnace is overheating the board should give you a code but not always.

 

When the furnace shuts down unexpectedly does the inducer and blower continue to operate?

 

May be issue has gone bad to worse..

in middle of night i woke up and notice system going in cycle... i go to furnace and no LED indicator. So i turned off thermostate and furnace for two minutes and started again.. and as soon as termostate sends signal to turn on furnace.. inducer fan turns ON then ignitor turns ON and then after 1-2 seconds.. ignitor turns OFF.. i see RED LED blink twice. According to panel - it means 'pressure switch is open with inducer ON'

Now does that mean its pressure switch gone bad or still could be something else?

 

It is actually rare for a pressure switch to fail. Check all the tubing and the nipples to tubing attaches to for free passages. You may need to take a series of drill bits to clear the passages in the nipples.

 

was doing some checks on pressure switch and types etc..

Anyway so this pressure switch only has 1 tube.. i tried to look at tube for any issues.. as i was inspecting tube end connecting inducer motor side...light pull took broke tube .. leaving portion on inducer section pipe.

I took those remaining parts out and cleaned and reinserted tube back in.

restarted furnace and it started fine.. ran for about 15 minute without shutting down.. however i still noticed two things after 7-8 minute of successful run..
- at one point lot of clicking sounds.. like relay switching on/off
- just right around those clicking sound... all three gas turned off for less than half a second and turned back on... its like "puff' (hope it makes sense)

Also no LED blinking when that happened.. all showed normal operation.

 

It sounds like you are narrowing down the cause of your issue. I suggest you double check the nipple where the pressure switch hose attaches to the inducer. The hole in there is very small and has to be clear all the way through. As Furd stated, a small drill bit is a great tool to ream out that port.

 

That might be a flame sensor problem shutting down the gas valve momentarily because of a perceived loss of flame. Remove the sensor (generally only one screw) and thoroughly clean the rod with a Scotchbrite pad and then replace.

 

Update.. So far it's been running fine after fixing that pipe. Cold weather is coming next week so will keep an eye on it.

Thanks everyone for your help.

 

Glad to hear it is still working for you and thanks for the update!

 

What are the parameters by which the flame sensor works? i.e. If the flame sensor is super dirty, for example, does that prevent the gas from lighting (no flame) in the first place, or does the gas always flame and then the dirty flame sensor would make the gas turn off because no flame is sensed by the sensor. I'm assuming it's the latter (because you'd need to have a flame in the first place for the sensor to be able to sense a flame if the rod is clean enough to sense one) yes?

 

The flame sensor works by a process called flame rectification (Google that for more information). It has no bearing on the initial lighting of the main burner but most systems have a four second timing from the time the gas valve opens and the flame must be sensed. If no flame is sensed within this timed period then the main gas valve closes. Some systems will then "lockout" any further attempts to light where others will attempt ONE relight sequence.

In operation the sensor will have a tendency to oxidize on the surface. This oxide can seriously reduce the already tiny current that flows through the flame causing a "no flame" signal. Scrubbing the sensor rod with a Scotchbrite pad will remove this oxide. Some people advocate sandpaper, emery cloth or steel wool but all of these will severely scratch the rod making it much more likely to oxidize to the point of not working in the future.

For what it's worth, my furnace was installed in the spring of 2006, serviced in 2007 and the flame sensor has not been touched since. It HAS had a problem with the pressure switch connection on the induced draft fan clogging but no problem whatsoever from the flame sensor.

 

Alright guys.. i am back.

its been very cold last few days and I started having same symptoms again...

Basically furnace turn ON with hot air.. runs for 4-5 min then several back to back clicking sound and system turns OFF. As usual NO LED indicators to show any problems. RED power LED stays solid and yellow flame sensor LED stays ON while system is ON.

When system stops unexpectedly inducer motor turns off and main blower fan stays on for 3+ min then turns OFF (that i think is normal as before but correct me)

So far i have replaced flame sensor, cleaned and reconnected pipe to pressure switch. All vents are clean and have new filter as well.

Any thoughts?

 

It sounds like the furnace limit switch is possibly opening due to high temperature condition. However, the inducer motor is supposed to operate along with the blower until the unit is cooled off sufficiently. Are you sure the inducer does not run for awhile after burners turn off. The service manual linked in post #2 explains the sequence in paragraph #12 on page 34. I suggest you make sure the air filter is clean, all of the air registers are open, the vent pipe is clear of obstructions, the a/c coil (if equipped) is clean, the return air ducts are not blocked by furniture or other objects. These things are the common causes of the limit switch to open.

 

I do have clean filter and intake/outtake vents. I just cleaned all vents couple days ago as well. I even tried running system without filter and same issue.

About inducer.. yes it does turn off when system turns off..in 30+ seconds. About circuits inside.. infact i just video taped that failure operation.. not sure how to share with you guys other than youtube.

 

The control board usually will show a fault code (see attached) when it shuts down. The fact that it does not give a code might be a thermostat related issue. Is the thermostat battery operated? If so, are the batteries weak as low batteries will cause erratic behavior of the thermostatic and cause operational issues? To troubleshoot, you will need to use a voltmeter to test voltages to see if you can find the issue. Probably the best method to share a video is to upload it to youtube and then post the link.

 

Here's video link - https://www.youtube.com/watch?v=QIxiLTO9MTk

at 20 sec - random clicking
at 1:20 min - inducer tuns off..
on middle right - you may notice 2 LED's - RED on top and YELLOW on bottom

I just uploaded it, so let me know if any issues viewing it..

 

The video worked fine. To me it sounds like there is water inside the inducer motor assembly.

 

what could be cause of it or how to fix it?

 

I am not positive it is water in the inducer since it is a video and taped sounds can be deceiving. Does it sound like water in the motor to you. Do you have a condensate drain? If so, you will need to check the collector box and ensure drain hose/pipe is not clogged up and is draining freely.

 

From furnace i do have drain pipe going to near by drain but i thought that's normally during AC operation and it does work during that time. Should inducer be usiing same drain? If not then i dont have any other pipe going to drain.

i listed to inducer sound again and doesnt sound like ther is any water but i guess i never heard one with so hard to tell. But question.. if that's the case i am guessing limit switch will or pressure switch should trip too..isn't it?

 

If it doesn't sound like water is in it then there probably is not. My next suggestion is to see if the thermostat may be the issue. You can bypass the thermostat by placing a jumper wire between the R and W terminals at the control board and see if the issue still continues. A short piece of wire or a paper clip will work. After you install the jumper wire press in the door switch and the furnace should go through the ignition sequence. If the furnace behaves properly with the jumper then you have a thermostat issue or a wiring issue between the furnace and the thermostat. If you do the use R-W jumper only use it for testing purposes.

 

i had tried R and W jumper earlier but at thermostate end but i will try again tomorrow at control board end.

so when i jump those system starts but when does it stop using that process?

 

I am not sure I understand your question. If you are asking how long the furnace will operate, it will run until you remove the R-W jumper or it shuts down on it's own due to an unusual condition.

I watched your video again. It is difficult to tell what the LEDs are doing. I look at the reflection on the back of the cabinet and I can only see one light being reflected and at one point there appears to be a red flash. Can you make another video concentrating only on the LEDs and where they clearly can seen?

 

About bypassing thermostat - i remove thermostat complete.. disconnected all wires as well then connected jumper as you mentioned. In summary same issue.. runs for couple minutes and several clicking sound and turns off.. then same repeats.

About LED's.. i can assure you it worked as manual said.. RED stays solid all time and yellow/organge turns on with flame and turns off when system shuts down.

 

another thing.. i unplugged pressure switch and flame sensor one by one to make sure control board lights up with LED error codes and it did.. so may be that one looks fine.. at least from LED error point of view.

Could there be any possibility of gas valve being bad? is there any test i could do?

 

The way to test the gas valve is to measure for 24V at the terminals right after the igniter powers up. I believe the wires are yellow and brown going to your gas valve and those are the two terminals where you will test. You will need to have the voltmeter set to volts AC and have the meter leads in place on the terminals. If the control board is sending 24V to the gas valve and it doesn't open then the gas valve is bad. If the control board doesn't send 24V to the gas valve when the ignitor is powered up there may be a limit control open or it could be a bad control board.

 

My water heater was doing similar things as to what you are describing and it turned out to be they put a screen under the burner that was getting clogged with dust and causing the fire chamber to overheat and shut down the burner. All I did was stuck a hose from my air compressor in the chamber and blow out the dust and hey, it works again. I hope that this is all that your problem is. Let me know if this helped.

Lonnie

 

Maybe it is my eyes. but in the video I see a light go out at :25.

 

at :25 bottom yellow light turns OFF. that's flame sensor.. at that time flame went out so light turned off.. i think that's normal.

About gas valve you mentioned to check 25V at terminal and if not then its bad. Now looking closely...since gas is starting i am thinking board is sending 25v otherwise it would not turn on at all, isn't it?

beside i am open to any other troubleshooting you suggest, i do have multimeter at home.

 

If the gas valve is opening, the control board is sending 24V. These types of issues can be a bear to figure out. I suggest you call for heat and with voltmeter set to volts AC test across the W and C terminals on the control board and see if 24V is continuous all the way until the time the furnace shuts off.

 

Three things i did

Gas valve - i disconnected two cables connecting to valve and connected volt meter to AC setting. when heat was not called i was getting 13.5V constant and when heat was called in after HSI came on.. i got 27V.. after few second it went back to 13 because i think system didnt recognize flame.

Limit switch - I removed cables from limit switch and connected jumpers in between. basically bypass switch.. (for 2-3 min).. and furnace came on with hot air for 3+ min and same symptoms.

Connected AC volt meter between W and C - i got contact 25.5 volt.. when furnace stopped unexpectedly i still continue to receive 25.5 volt (thermostat was calling for heat)

 

Next I would test to see if the pressure switch is closing and staying closed. To test to see if it is closes and stays closed with the inducer running use your voltmeter set to volts AC and see if you have 24V to ground on either terminal. Across the terminals it will read 24V if open and 0V if closed. You will need to monitor the pressure switch voltage all the way up until the furnace shuts down.

Then you perform the same test on the high limit switch to see if it may be opening during operating causing the furnace to shut down.

During the series of tests you did, when it operated for 3+ minutes did the blower come on 30 seconds after the gas valve opened?

 

Video attached - http://youtu.be/mp4q-Sq7vjw

I connected AC volt meter between one connector of pressure switch connector to ground. So when inducer motor came ON i saw 26+V but looks like just around lot of clicking sound (@30 second in video)... for 2 seconds.. that voltage dropped to almost in single digit and came back to 26+V again... but by that split second gas was turned OFF.

In summary looks like pressure switch gets open for unknown reason then furnace shuts off.. then switch is closed back again.. not giving any LED indicators on board.

Does that mean its bad pressure switch or what do you think?

 

Pressure switches rarely fail but sometimes the contacts get weak. As a test I suggest you remove one wire from the pressure switch and call for heat. As soon as the in inducer gets up to speed place a jumper wire between the two pressure switch wires and monitor operation of the furnace.