Author Topic: Lennox Whisper Heat starts to work after reset  (Read 12206 times)

Offline starmount

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Lennox Whisper Heat starts to work after reset
« on: March 17, 2008, 08:37:02 PM »
Hi Guys,
I have 15 years old Lennox Whisper Heat gas furnace installed in my house. Fall last year we had the furnace serviced - cleaned and checked. After a month or so it stopped working. The technician came and found that the ignition control broke. He replaced it with new electronic one: Honeywell S8610U.
It had a problem to start after a long delay (if there was a sunny and not cold day). The technician came again and checked everything (cleaned pilot assembly again, wiring, etc.) Then I think because it was very cold and the furnace had to work all the time, it worked fine, only sometimes did not start from the first attempt - the module has retry and from the second/third attempt it was starting.
Now it is time when furnace does not start too mach during the day, so in the evening it doesn't start at all. The only thing that helps is SHUT OFF THE MAIN POWER SWITCH AND ON AGAIN.
If it doesn't start the sequence is:
1. Call for heat;
2. The ignition spark starts;
3. Pilot lit;
4. Spark stops;
5. The pilot burns for some more and then there is a click of the valve and the pilot shuts off.

Once reset the furnice will work until the next long pause before the call for heat.
According to the troubleshooting guide of the ignition control unit it looks like the problem is in the gas valve, but why the heck reset helps then?
The technician cannot say and offers to try and replace valve, pilot assembly, sensor or the entire furnice...
Thank you in advance!

Offline TECH X

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Re: Lennox Whisper Heat starts to work after reset
« Reply #1 on: March 17, 2008, 09:37:48 PM »
If the module fails 3 times at lighting it goes into a lockout.  Resetting the power is what resets the module from this lockout.  You're right, the gas valve itself does not need to be reset.  The module sends 24V to the gas valve's PV terminal and that sends gas to the pilot, then the module sends 24V to the MV terminal and that sends gas to the burners.

You hear a click at the valve after the pilot is lit...then do you hear a second click before the pilot goes out?  How long after the first click is the second click?
You have to verify there's a constant 24V to the gas valve, long enough for it to open and fire.  An intermittent gas valve problem would be rare for that model.

You can only guess until you get readings with a multimeter.

Offline HVACJOE

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Re: Lennox Whisper Heat starts to work after reset
« Reply #2 on: March 18, 2008, 07:34:04 PM »
You definatly need a multimeter reading, often you will find a voltage drop through your limits ( be it ventor air proving, high limit, rollout etc..) and this will cause a lower voltage to the valve resulting in intermittent operation. However without more information to diagnose the problem, its very difficult to provide you with a soloution

Offline starmount

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Re: Lennox Whisper Heat starts to work after reset
« Reply #3 on: March 18, 2008, 08:46:50 PM »
If the module fails 3 times at lighting it goes into a lockout.  Resetting the power is what resets the module from this lockout. 

Thanks for the reply.
It doesn't go into lockout, because the ignition module has been marked as: "Continues Retry", so it tries forewer...
I checked it again today - it doesn't do the second valve click, so main gas stream doesn't start. And then I hear last click of the valve - closing of the pilot.
It looks like flame sensor problem. I think I'll look into the replacing of the pilot assembly... The only thing that makes me hesitate  is - the fact that the spark stops once the pilot flame starts to burn, so something sends the signal about it to the ignition control unit. And it is dome by the sensor.
Do you know if the flame sensor has levels of signal? Or it is Yes/No type of thing?
Thanks

Offline Admin

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Re: Lennox Whisper Heat starts to work after reset
« Reply #4 on: March 19, 2008, 03:43:30 PM »
That's what I thought as well.  You probably have the newer S86IOU1003 or S86IOU3009 module.  The 3009 will actually have a yellow LED light that will indicate whether the flame signal is sufficient or not.  BTW the 3009 module is about $100 cheaper then the 1003, and is better in my opinion.  If you have the 1003 you'll have to measure your flame signal with a multimeter that can measure Ua (micro amps).  Disconnect the flame sensor wire from the module.  Connect 1 meter lead to the wire and the other to the module "SENSE" terminal.  You should have at least 1.0 Ua when the pilot lights, then after the burner fires it can go higher around 3.0 Ua.

The easy thing to do is just clean the flame sensor, and see if that helps correct your problem.  It should be done yearly.

Offline starmount

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Re: Lennox Whisper Heat starts to work after reset
« Reply #5 on: March 21, 2008, 01:18:26 PM »
The module has the amber light, but I dod not understand how it should light... It is kind of blinking, but not with constant pace when the pilot starts to burn... and if the main burner starts it blinks with the heart beat pace.
Unfortunately I don't have any microampermeter... mine is milli only, but I tried to remove the pilot assembly to clean the sensor. One of the screws of the assembly got stuck, so I removed the sensor only. It looked perfectly clean, but I still cleaned it including the contacts and put it back. The first start was OK. I will watch it longer to know if it helped.
Thank you so much for the help!

Offline IdealHomeComfort

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Re: Lennox Whisper Heat starts to work after reset
« Reply #6 on: March 30, 2008, 02:01:53 PM »
Before anything else you should have the heat exchanger checked for cracks, the heat exchanger is the same as the G8 but usually the whisper cracks around the 13 year old mark and