Author Topic: Lennox modulating furnace  (Read 832 times)

Offline harshal

  • 313D Supporter
  • ****
  • Posts: 118
Lennox modulating furnace
« on: February 12, 2017, 03:58:22 PM »
Working on the Lennox modulating furnace with the communicating thermostat and it been locking up with calibration issue for the low pressure switch.the model number of the unit is SL98UH090v36v-01.checked the vent and air intake both are clear.any thoughts?

Offline Admin

  • Administrator
  • *****
  • Posts: 2226
Re: Lennox modulating furnace
« Reply #1 on: February 12, 2017, 05:50:54 PM »
How does the drainage system look?

Lennox has had their share of pressure switch problems.  I would try replacing that.

The manual says for upflow installations the P-Trap can be installed on either side of the furnace, but I have read where installing it on the left side can cause problems.

Offline walker

  • Pro Tech™
  • *****
  • Posts: 515
Re: Lennox modulating furnace
« Reply #2 on: February 12, 2017, 07:10:21 PM »
check the pressure ports themselves, had more than a fair share of those plug up with crap, I usually take my tiny screwdriver and poke it through the port a few times to clear up any crap in there.  I have also had an instance where the board itself was just giving that false error and changing the board fixed it

Offline Sergroum

  • Pro Tech™
  • *****
  • Posts: 111
Re: Lennox modulating furnace
« Reply #3 on: February 17, 2017, 03:48:17 AM »
Dont forget that on this furnace there are actually two holes behind the Ventor Motor on the collector box. There is the big huge hole that you cant miss and a tiny one that can be missed easily and can get plugged up with crap.

SLP98 is pretty known for having very crappy pressure switches. They've released a (hopefully) improved version. I think they just changed the location of the port for one of the tubings there.