Lennox LGA120 Heat lockout

[Eights]

I'm kind of at a loss on this unit...

When I arrived on this call, I diagnosed it with a bad ignition module (Had 24 volts to it with no spark). Changed the ignition module and everything was fine. Burners fired, blower came on etc. As I stood on the roof making sure there was no roll out, checking the filters, belt, etc., the system shut down. Lost lights on the board(s) and nothing ran. Reset the unit (disconect off/on) and everything fired right back up...For about 2 minutes and the thing locked out again. It's not giving me an error code. I haven't dealt much with the L series Lennox units so I'm not just real sure where to go from here. I thought it might have been 2nd stage heat causing the issue but it still locks out with 2nd stage heat disabled. Will this scenario happen if a limit opens?

Any suggestions would be greatly appreciated.

[james mo]

Are you losing ALL of the lights and the led code display or are you just losing the input lights on the lower left of the main control board...??

[Eights]

I'm losing all of the lights and the led code display.

[Octopus]

Is something breaking 24 volts the the control board, or bad control board when you power it back up it should show err for losing power at least and have any others stored under recall. The safety's are on the plug going into the main control board I think plug p1111 or something like that.

[Eights]

Wow...I feel stupid. I went back this morning to take another look and found the problem almost immediately.

Whoever installed this unit hooked up the smoke detector to the 24v terminal strips right off of the transformer. When they did, they drilled a hole right next to the strip and ran the thermostat wiring behind the control panel. With the wiring that was already there, it made it real difficult to see what they had done. I completely missed it when I was there the first time. I made this way more difficult than it was.

The heater hadn't run in a few years (according to the customer) and once I got it going it was burning off years of build up on the heat exchanger and tripping the smoke detector which is why it was only running for a short period of time and then losing voltage at the board.

All is good now. Thank you guys very much for the replies and input. Much appreciated.

[Octopus]

Theres a fire alarm input to stop unit operation and even a dry set of contacts provided on those units if I remember right, they should have never cut into the unit like that.

[tvmanjon]

4k sq ft block building poorly insulated 1 1/2 " poly iso flat rubber membrane roof. Some perilite in block and 1" board under drywall to 8' height dividing into 3 suites with seperated walls. Each unit has typical retail entrance doors with 100 sq ft or less windows. Unit 1. 2000 sq ft 2. 1300 sq ft 3. 800 sq ft Planing on seperate units in each. Unit 1 is going to be a CubWay Restaurant and they are handling HVAC. Unit 2 contractor says 4 ton but choosing 5 in case we decide to H/C suite 3 with it. Contractor prefers Carrier WeatherMaker but gave me choice if I have a preference
.1 Any opinions?
2 Will insulating the duct supply and return be much of a benifit? They wrap with foil faced 1" ?
3 Opinion on spray foam polyurathane for underside roof deck? Open/Closed cell?
4 What else should I ask? Thank you Jon