Lenox Elite Series - flame out

bhamberg

Hoping for an easy solution (yea, right :O)). Dewinterizing a large home with 4 (Lenox) split units. 2 (vertical) units in basement fired up and are working normally. 2 (horizonal) units in the attic fire but will not stay lit (seems to start normally but flame shuts off after 3-5 seconds). LED flash normal on restart then LED 1 & 2-alternating, slow flashing (flame failure).

(EDIT: both attic units are doing the exact same thing!?)

House sat vacant for long time with gas off - I bled out the lines prior to restarting. Anyone have a simple test or answer from past experiences?

EBEBRATT-Ed

Clean the flame sensors or replace if HSI

bhamberg

Cleaned the flame sensor, restarted and the exact same thing happens. I removed the inlet (2" PVC) from the manifold and the unit fired and ran normally.

Any ideas on next steps troubleshooting?

EBEBRATT-Ed

So if i understand you comments cleaning the flame sensor didn't help but removing the air intake pipe did?

If so either the intake is blocked, birds nest etc or you have an issue with the pressure switch. Take the tubing off the pressure switch and make sure it is clean

bhamberg

EBEBRATT-Ed said:

...or you have an issue with the pressure switch. Take the tubing off the pressure switch and make sure it is clean

@EBEBRATT-Ed - thanks, no blockage in the air intake and the rubber tubes blow-through. Tried jumpering the pressure switch but the unit didn't fire - guessing there is a procedure I'm missing? Is there a resistance test? (not normally about replacing to test, and would do, but they are very proud (expensive) of their pressure switches - hate to buy without first isolating the switch.

EDIT: if relevant, there are 2 units both doing the exact same thing and both sat in a vacant home for 1-2 years

JUGHNE

Condensing furnaces in the attic for 2 years of freezing.
Possibly some part of the drain system froze and cracked giving you a small air leak on the suction side of the fan. Just enough to keep the switch from closing.
Removing the inlet pipe drops the inlet resistance enough to close switch.

Some pressure switches are checked that they are in NO position before the sequence begins. Then after fan starts they move to NC. to go for ignition.

bhamberg

JUGHNE said:

...Possibly some part of the drain system froze and cracked giving you a small air leak on the suction side of the fan...

@JUGHNE - I'd agree on one unit but both are doing the exact same thing?? (still possible I know) Got 2nd hand info there is a specific procedure for testing the Lennox pressure valve (think they call it an Air Prove Switch?) but can't find any details on the procedure.

mattmia2

You should be able to find the manual with the troubleshooting procedures.

If both had condensate in the traps that was not drained out, both are very likely to have cracked. Be prepared for that assembly to cost like 1/4 the cost of the furnace.

bhamberg

mattmia2 said:

...If both had condensate in the traps that was not drained out, both are very likely to have cracked. Be prepared for that assembly to cost like 1/4 the cost of the furnace.

@mattmia2 how can I confirm for sure (short of a complete disassemble)?

mattmia2

Look and feel with a mirror or a phone around where the condensate pipe connects for cracks or condensate dripping out.If it looks or doesn't look like they removed the plug to drain the condensate might also be a clue.

EBEBRATT-Ed

@bhamberg

Most furnaces the pressure switch is open when the furnace is off. The circuit boar "looks at" the pressure switch and won't let the furnace start if the pressure switch is closed. That's why it wouldn't start when jumpered


Try this

Put you air intake back on.

Remove the two wires from the pressure switch. Put you ohm meter or continunity tester on the pressure switch terminals.

Start the furnace and as soon as the draft inducer starts jump the two wire you took off the pressure switch

Watch your meter/continunity tester . It should close when the inducer starts.

bhamberg

EBEBRATT-Ed said:

Try this

Put you air intake back on.

Remove the two wires from the pressure switch. Put you ohm meter or continunity tester on the pressure switch terminals.

Start the furnace and as soon as the draft inducer starts jump the two wire you took off the pressure switch

Watch your meter/continunity tester . It should close when the inducer starts.

Heading back out there on Friday - will keep you posted!

bhamberg

EBEBRATT-Ed said:

@bhamberg
Put you air intake back on.

Remove the two wires from the pressure switch. Put you ohm meter or continunity tester on the pressure switch terminals.

Start the furnace and as soon as the draft inducer starts jump the two wire you took off the pressure switch

Watch your meter/continunity tester . It should close when the inducer starts.

Update and some thoughts on logic (or not).

• Intake was back on
  
• Unit switched off - continuity tester is open
  
• Unit on - continuity tester closed (see video for readings)
  
• Switch is jumpered and unit flames out at 5-7 seconds
  

Video: Meter video

In my (feeble) mind this would indicate the switch (as it was jumped) is working?

(edit: I'd go back to a Flame Sensor issue but again the unit works with the air intake off, which, indicates a pressure problem somewhere which loops us back to the pressure switch which was jumped and the unit still flamed out...)

JUGHNE

Is there another pressure switch, on the exhaust for example?

Is the exhaust pipe clear?
Would the exhaust piping/inlet piping exceed the specs for length/fittings?

bhamberg

JUGHNE said:

Is there another pressure switch, on the exhaust for example?

Is the exhaust pipe clear?
Would the exhaust piping/inlet piping exceed the specs for length/fittings?

@JUGHNE - only one on these units (2 units doing the exact same thing) and no, they had been in service for 10+ years.

HVACNUT

bhamberg said:

@JUGHNE - only one on these units (2 units doing the exact same thing) and no, they had been in service for 10+ years.

More like 20+ years.
What are the model numbers?
Can you post a pic of the wiring diagram?
Nat gas or LP?
Dirty orifices and/ or burners, flame not getting across to the sensors?
Because of the age of the equipment, and because they sat neglected for a couple years, it would be wise to have them (all 4) checked by a qualified tech. Even if you can get them running, it doesn't mean they're running safely and efficiently. Testing the heat exchangers on the attic units would be my main focus.
 

bhamberg

More like 20+ years.
What are the model numbers?
Can you post a pic of the wiring diagram?
Nat gas or LP?
Dirty orifices and/ or burners, flame not getting across to the sensors?
Because of the age of the equipment, and because they sat neglected for a couple years, it would be wise to have them (all 4) checked by a qualified tech. Even if you can get them running, it doesn't mean they're running safely and efficiently. Testing the heat exchangers on the attic units would be my main focus.
 

@HVACNUT :

• 21.5 to be exact! (**99G**)
  
• 50K units GHR26's Q2/3-50-4 horizonal mount.
  
• No pics of wiring - sorry
  
• NAT
  
• I can watch it ignite, flame amount & color is good
  

And, yes, if it comes to it they will get a "qualified" tech out but - and this is more for my edification at this point - I'm responsible for qualifying their findings.

The part I'm having trouble with is, it lights and works properly* with the intake off.

Correct me if I'm not thinking right (my wife does constantly!) but, doesn't that eliminate the flame sensor? AND, if the pressure switch is "jumped", is open on start and closed after the blower starts, that eliminates the switch? So why do BOTH UNIT work with the intake(s) off??

EBEBRATT-Ed

@bhamberg
You have to make sure that the flue and more important the intake is clear. You could have a wasp nest, birds nest or something in there. The intake pipe could have a sag and be partially full of rainwater/condensate.

Does the control board have any lights that blink to show codes.?

Is this standing pilot, flame rod hot surface ignition or what??

I would also check any wiring particularlly any ground wires between the ignition module/control board and the burner/flame sensor

bhamberg

EBEBRATT-Ed said:

@bhamberg
You have to make sure that the flue and more important the intake is clear. You could have a wasp nest, birds nest or something in there. The intake pipe could have a sag and be partially full of rainwater/condensate.

Does the control board have any lights that blink to show codes.?

Is this standing pilot, flame rod hot surface ignition or what??

I would also check any wiring particularlly any ground wires between the ignition module/control board and the burner/flame sensor

• Both units use a 3" concentric (roof) termination. What is the best way to verify they are clear, WITHOUT "ME" getting on the roof - not a fan of heights!!! Plus it's easily a 16/12 pitch!

  1st unit is maybe 15' to the roof.

  Unit 2 is 30'

• 2-led's alternating slow blink (burners fail to ignite.)
  
• It's electronic ignition
  

SuperTech

I'm betting that the intake or flue pipes,  possibly both are blocked by something.  Birds nest, wasp nest, dead animal or something similar.  Get some couplings, glue and primer and cut them open and find out. PVC glue and primer plus a few couplings is a cheap investment that could solve this problem or eliminate the possibility of blockage. Or just take the piping off and see if anything changes.  

bhamberg

SuperTech said:

...Or just take the piping off and see if anything changes.

@SuperTech - exactly what I did and if the intake is disconnected at the manifold, the unit fires and runs as normal.

(EDIT: 2 units doing the exact same thing!)

SuperTech

Then you know what the problem is! Intake is blocked somewhere.  Use a sawzall,  hacksaw or PVC cutters and open it up close to where it goes outside.  Thats most likely where the blockage is. Since its the intake pipe using glue and primer isn't critical when putting it back together. (But it's the right way). You could also use a rubber Fernco coupling that utilizes large hose clamps to keep the piping together.  

It could be blocked at the concentric fitting itself,  then you have to go to the roof if the blockage can't be cleared from indoors.

bhamberg

@SuperTech heading back today, seems peculiar both would have the exact same problem but I'm up for a step-by-step trouble shoot. WKYP