Lennox G27M Shutting Down

______________________________________________________________________ Help – my family is freezing the middle of the night! Have a Lennox G27M (6 years old) it has been shutting down following some clicking noises (about 2 seconds long). Sometimes it will start back up but most of the time it will not. When it does not the t-stat is reading the heat is on. The only way I get it back on is to switch the t-stat off and then on again. Any Help would be greatly appreciated! Replies: acefurnacefixer “Re(1):Lennox G27M Shutting Down” , posted Sat 10 Dec 08:23 ______________________________________________________________________ The flame sensor is dirty…….you and your family is cold tonight because you dident have a pre-season check up.Go tell your kids your a bad Dad! Yes! I CAN fix that! moondog “Re(1):Lennox G27M Shutting Down” , posted Sat 10 Dec 03:48 ______________________________________________________________________ Probably be best to have a Lennox dealer look at it. Sometimes it is the boards and sometimes a connection. Since the burners don’t light and then go out, you can rule out flame sensor that may need an upgrade. G27M “Re(2):Lennox G27M Shutting Down” , posted Sat 10 Dec 12:55 ______________________________________________________________________ Moondog – Do you mean a flame sensor upgrage? Didn’t know of such a thing…can you direct me to site I may find more information? I did have a Lennox Tech. look at it a week ago… Got the feeling he didn’t know what was wrong…blammed it on possibly an a required altitude kit? He also thought the exhaust duct might be sized too small? – Overall his guess as good as mine. I just cleaned the flame sensor, problem did not go away. not dave “Re(3):Lennox G27M Shutting Down” , posted Sat 10 Dec 13:02 ______________________________________________________________________ I have had many problems with the g27 and pressure switch codes…left light off and right light slow blink on diagnostic lights. I have not found an answer from Lennox on this. They send me out an updat kit that has a new inducer and pressure switches but does not seem to help. I don’t know if this is related to your problem but just letting you know what I know. Which is just about nothing. I know just enough to be dangerous…heh heh… G27M “Re(4):Lennox G27M Shutting Down” , posted Sat 10 Dec 13:17 ______________________________________________________________________ NotDave- Thank you for the information. Ok – my sequence of failure is as follows; 1) Furnace starts 2) About 10 minutes into heating…flame goes out. (clicking noise) 3) Electronic ignition starts…burners re-light. 4) This will occur about 3 to four times in about 30 to 40 min. time span. 5) On the third or sometimes 4 try the burners do not light back up. 6) The diagnostic code reading is “Watchguard–burners failed to ignite”. Again, I have cleaned the flame sensor – do you all think it could be the pressure switches? not dave “Re(5):Lennox G27M Shutting Down” , posted Sat 10 Dec 13:30 ______________________________________________________________________ It is difficult to say for sure. Getting a reading off the flame sense would be helpful, but I really don’t think thats the proplem, if it runs fine until 10 min later. The 10 min later is the furnace going into high fire, which suggests to be that the two stage control board (the smaller green circuit board) might be bad. I’m starting to woner if this is the problem with all of these… I know just enough to be dangerous…heh heh… not dave “Re(6):Lennox G27M Shutting Down” , posted Sat 10 Dec 13:43 ______________________________________________________________________ Iread your post again, and it sound to me like a relay on the control board is causing the problem. When the furnace goes into high fire, the inducer and blower kick up a notch in speed. If the relay controlling the speed of the inducer causes it to stall briefly, this will cause the pressure switches to momentarilly break their electrical contacts, which will immediately reset the furnace to re-ignition. Five times and the furnace will lock out into watch gard. I am working on a similar issue right now. Its been a real head scratcher. I know just enough to be dangerous…heh heh… G27M “Re(7):Lennox G27M Shutting Down” , posted Sat 10 Dec 14:14 ______________________________________________________________________ NotDave – I think you might be hitting it right on…. The furnace does go into high fire – just before failure… I’m not going to try to install a relay on my own…can you give me more information on the exact relay I should have a technican look at? (I have no idea where it is?) not dave “Re(8):Lennox G27M Shutting Down” , posted Sat 10 Dec 16:55 ______________________________________________________________________ You have to replace the whole board. Its the smaller green board above the larger circuit board. Or you may have the intellignition board, which is all on one board. Just trace the wires from the inducer to the source, and thats the board. You can try something here to see if it will make it work until you can replace it, or possibly discover its a different problem altogether. The board you are looking for has a 9 pin connector on one side, and a 6 pin connector on the opposite side. Its the smaller board, not the one marked ‘Sure Light’. On this board is a jumper block marked ‘Two stage-one stage-w2 timed’. You can try this: shut off power and move the jumper from ‘w2 timed’ which I’m guessing is where its at, and move it to ‘one stage’ and then restore power. This will force the funace to work in high fire only. If you are still having problems, you know what the problem is then. Give that a try. I think the problem is the swith from low fire to high fire. I know just enough to be dangerous…heh heh…

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