Lennox

[wesgarrison]

First time poster, I'm hoping someone can give me a hand.

I've got a gas furnace that ignites, but won't stay lit. 

It's a Lennox 80MGF3-75A-5 .  See pics for details.

Here's the sequence of events:

• thermostat sends ON signal
• small blower above starts
• ~10 seconds elapse
• ignitor spark starts clicking
• gas turns on and I can see flame on all five burners
• ignitor keeps clicking
• burners run for 10 seconds-ish (with the ignitor still on)
• burners and ignitor shut off
• repeat, total of five times
• fan shuts off
• circuit board shows alternating LEDs

The message on the panel for the alternating LEDs is:

Watchguard - burner failed to ignite

I had a service call and he wants to replace everything for $1000 or sell me a new furnace.  Seems to me that everything is working, it just won't stay on.  Perhaps this is a common issue with this brand?

Any advice much appreciated.

EDIT:

Sorry, I meant to put more info in the title.  If a mod sees this and wants to update the title appropriately, that'd be nice.  I can't find where to do it.

[RegUS_PatOff]

I'm no expert, but how's the Flame Sensor ?

80MGF Service Manual

 

[wesgarrison]

Dirty, dirty sensor. Thanks for the link to the manual, it helps to know what all the parts are!

I pulled apart the five burners, cleaned both the flame sensor and the ignitor, got all the dust out of the burner cones, and put it all back together.

It's started up several times in a row just fine.

Thanks a bunch!