Lennox EL296V error 229

I would not worry about it. Years ago most furnaces started in high fire to get a good flame established and then dropped to low after 30 seconds. That is not uncommon practice. My sister's new 2 stage Rheem is programmed for that. Low fire pressure switches are set very low and are sensitive to venting etc. Lennox just wants to start the furnace is a safe condition with enough draft/venting and once it fires/warms up the draft changes anyway so it is fine. Newer furnaces are very sensitive to draft and to get 95% and higher efficiency and the small physical size of the heat exchanger compromises have to be made. Check the venting outside for obstructions. I would not try start a furnace on low fire as the gas pressure/manifold pressure is so low that getting a good stable flame quickly is hard but I suspect they are trying to do that to make the furnace quieter for advertising purposes. No problem starting it on high fire.

Thanks, that's very insightful, you are right, the noise level between high & low fire is huge, and that's why I got a bit concerned / annoyed.

Could be the venting is too long, or not big enough for the low fire pressure switch to close when the inducer is running in low speed to start the heating cycle.

if you have the install manual find the venting table chart and measure the venting length and add the equivalent feet of pipe due to the elbows to make sure they installed it properly. easy to understand in the manual.

The installer used 3" pipe for my 90K BTU model, according to the chart, either the intake or the exhaust can go as far as 73 ft (standard termination) with ten 90 degree elbows, I measured my furnace's intake and exhaust pipe length, they are about 20 ft each with 4 elbows, way below the allowable limit. Thanks,

Check for a restricted trap.