Not the usual flame failure - Lennox G71MPP-60-090.

[BobOfMN]

Hello HVAC-Talk,

My background is electrical control, automation, and networks - the drive guy on commercial and industrial jobs.

This is not the usual flame failure problem.

I installed a G71MPP-60-090. Met all the specs for venting, condensate trap, return and supply air. Set the control board board for a single stage thermostat and started-up.

It ran perfectly for the first day as I buttoned up misc. things.

Day 2, it started to have flame failure -Error Code 273. Day 3 no successful starts - again flame failure.

According to the flow chart when calling for heat, observation of the flame and timing, it goes through start-up calibrations, ignites and is statisfied there is a flame. The flame is robust.

I think it also properly goes through the stabilzation delay but not sure. I think it flames-out when it goes to low firing rate.

I've turned all other gas using appliances to possibly mimic day 1 - no help. I toggle the dip switch 1, back and forth to recognize a single stage thermostat. I checked the vents for obstruct. Today the outside temperature and wind are almost like day 1. I'm still having flame failure.

I'd appreciate and suggestions.

Thanks
-BobOfMN

[jtrammel]

Proper grounding is critical on high efficiency furnaces. No DIY get your post count up and apply for pro membership

[Joehvac25]

I've seen that before, read the manual, without giving advise I'd say its in the setup instructions maybe.


Sent from my iPhone using Tapatalk

[Joehvac25]

S

[BobOfMN]

Thanks jtrammel,

Ground, neutal, and the gas pipe are the same potential. No current in ground.

I'll watch the site now that I'm semi-retired and have time. I'm not sure if I can be of that much help in residential, but maybe there is some cross-over from my old commerical and industrial days.

-BobOfMN

[syndicated]

Make sure the flame sensor wire isn't cut or grounding out to the frame.
Make sure the sensor itself isn't touching the burner, that its screwed in sercurly and its clean.

That can't be a new furnace since Lennox hasn't made them in 2 years.

[t527ed]

what size venting and how close to max allowed length? had 1 090 that was under chart limits but was doing same thing you described, had to go up to the larger size venting and issue was resolved.

[BobOfMN]

Thanks syndicated,

The sensor and wire is clean and proper. It is a new furnace. I got it in its orginal unopened box. It is a long story of a office/warehouse project
that had money problems.

-BobOfMN

[BobOfMN]

Thanks t527ed,

After a couple of 90 degress I had not planned on in the beginning, it is within a couple of feet of the max for the vent sizing. I was sort of concerned it. I can replace most of horizontal and the first 90 to vertical at the furnace with out too much problem.

-BobOfMN

[Joehvac25]

I have seen when gas pressure is to low on 1st stage furnace cuts out. How's gas pressure?


Sent from my iPhone using Tapatalk

[syndicated]

I have seen when gas pressure is to low on 1st stage furnace cuts out. How's gas pressure?


Sent from my iPhone using Tapatalk

Check gas supply pressure as well. That will be the first thing Lennox will ask you when you call in.
Those boards aren't known to be particularly bad, but you never know!
I believe on that board you can go into the config settings and see the signal the board is actually getting, although that might be hard to do since they do a vent calibration after power is cut.
Have you checked the actual uA signal from the sensor with your meter?
If the signal is good, gas supply pressure is good, and you know you have good ground back to the panel, I'd point my finger at the board.

[t527ed]

Thanks t527ed,

After a couple of 90 degress I had not planned on in the beginning, it is within a couple of feet of the max for the vent sizing. I was sort of concerned it. I can replace most of horizontal and the first 90 to vertical at the furnace with out too much problem.

-BobOfMN

what size pipe?