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Old 11-18-2012, 08:27 AM   #1
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Lennox SLP98 pressure switch issues


Hi -

We have a two-year old SLP98 furnace that will not light. I have had HVAC techs out three days in a row (at $160/visit) and still they really don't know what is wrong with our furnace. Each time they come out, they try a bunch of different things (mostly the same things the other guy tried), read the error codes and after a bunch of trial and error, the furnace lights again and we have heat for approximately 12 hours.

After the furnace stops lighting, it keeps trying to calibrate when heat is called for by the thermostat. The inducer comes on and then the pressure switch clicks, then it keeps ramping up, the pressure switch(es) click a few more times, it keeps ramping up and then shuts down, giving error code 228.

All of the venting has been checked and is clear, all of the hoses leading into the pressure switch have been blown out and are clear. All the wiring is intact.

Seems like the furnace just happens to come back on once in a hundred or more tries by the service tech. Once they get it on, they leave and tell us to call again if it goes off. The latest senior service tech said he thought the pressure switch might be bad, so we are waiting for them to order us a new switch. Of course, they can't get one on the weekend.

Anyone else had this problem? The service tech said he thought that he remembered something about the pressure switches for this unit having a problem. Has there been a recall of them?

Thanks for all replies.

Becky Snider


Last edited by beenthere; 03-18-2013 at 04:06 PM. Reason: Removed reference to her company
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Old 11-18-2012, 08:40 AM   #2
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Lennox SLP98 pressure switch issues


There have been a few failures of those switches but no more than average. The inducer needs to ramp DOWN to its lowest speed to calibrate the high and low aspects of the switch/venting. If it does not ramp down then it usually is the switch AND it is the dual pkg of switches unless you got the latest series which does not have a 3rd pressure switch. Have not had any problems with the latest version of it. THey also should be clearing the error codes off the board B4 they leave.

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Old 01-24-2013, 09:56 AM   #3
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Lennox SLP98 pressure switch issues


I am having the same problem with my SLP98. I was able to get it fired up last night for about 3 hours, but the unit was off again this morning. There is no drainage issue and the vents are clear. The manual says to check the wiring for the pressure switch after clearing the vents. Is there anything else I can do before a tech arrives to eliminate everything besides a bad pressure switch?
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Old 03-18-2013, 01:49 PM   #4
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Lennox SLP98 pressure switch issues


My slp98 behaves in a similar way: upon heat request the inducer spins up, and I can hear a click in the pressure switch. Then it spins for may be 20 sec, and slows down. When it slows down I can hear another click in the pressure switch. Then it stops and nothing happens. What can I do to fix this? The furnace is 14 months old. The furnace shows E228 error code on the thermostat.

Last edited by petyanca; 03-18-2013 at 01:52 PM.
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Old 03-18-2013, 04:15 PM   #5
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Lennox SLP98 pressure switch issues


call the installer or a certified Lennox dealer. parts should have a 10 yr warranty and there is nothing you can DIY with that furnace except check the vent pipes outside for blockage.
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Old 03-20-2013, 11:45 PM   #6
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Lennox SLP98 pressure switch issues


Sounds like a bad pressure switch, they are finnicky things. Wouldve been two weeks ago now we installed a new carrier 60k btu furnace in a place ans the next day got a call saying it wont light. Was the pressure switch. Im surprised it took two different guys to figure it out though

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