Lennox G50UH... Everything working but burner not???

nick_8

I have a G50UH I am working on and am stumped. It is only one year old. Everything is running fine( fans etc) but the burner wont ignite. The gas and all intakes/out flows are in working order. I have read about it could be the limit switch. it has a honeywell VR8205 gas valve. Please help if you can. This house has kids and it is near 0 degrees here in Michigan.

Nickk

Is the rollout switch tripped, you said the blower was running. Usually the newer models have a rollout switch w/ a reset button, try depressing it. Also, if that is the case, is the intake or exhaust plugged?

nick_8

thanks for the quick reply!!!!!!

My guy is getting a new air filter right now. old was pretty cloged. I am looking for a reset switch but there doesnt seem to be one on this model. atleast not one that is labeled. Thank you for your help again.

Nickk

is it a sealed combustion unit? i would guess that it is. it won't be labeled, it is similar in size and shape to an overheat snapdisc, probably the size of a quarter, check the side of the burner

nick_8

http://www.davelennox.com/pdfs/manuals/Lennox G50UH Manual.pdf

here is a link to the manual for the product. I am working on finding the switch but even the limit switch doesnt have any reset on it like most manuals say. Your advice has helped a ton so far. I will keep you posted.

nick_8

conceled unit

it says its a concieled unit and i couldnt find any switch on the bunner. there are two smaller disks(nickel sized) on top of the burner with short red things sticking out but they dont depress like buttons.

Nickk

if u tried depessing both of them, and that didn't work, follow the directions in the manual and shut it off in the same manner as they describe, wait more than the 5 min, the follow the instructions to relight to the letter.

nick_8

sweet man

sweet will do!!

Wayne_14

ignition failure

Did you check the air flow switch ?

nick_8

doh!!!!!!!!

new air filter. Follow directions for restarting. turned of gas etc. the self diagnostic still says "primary/secondary limit switch is open". I am checking the out tube but getting stumped here. everything else runs fine.

nick_8

air flow switch ????

I am not finding many switch in this unit. do you mean the combustion air proving pressure switch??

Wayne_14

yes

nick_8

Wayne??

How do I rest that switch. there is no info on it and there is no reset switch on the part??

Jared M

Limit Switches

That code indicates that one of two limit switches is open. The primary limit is located on the front panel, above the main burners. If this switch is open you will need a new one...they are not resettable in the field. The secondary limit is harder to get to and is usually a manual reset switch. If the furnace is installed horizontal and had a dirty filter it may be tripped. It is located on the back side of the main blower, you have to open the blower door to access it, just follow the two wires that lead to it, they are usually blue in color. Press in the small red button to reset that switch.

Hope that helps,
Jared

Wayne_14

Check that the blower door switch is made as well as the combustion blower switch. Of course make sure you have the gas valve turned on.

Wayne_14

You will need a meter to test it, or temporarily jump it for test only

don_12

Jared

got you going in the right direction.Check the secdonary
limit that attached to the blower housing.

But usally the main limit will lock out the burner and bring on the fan before the sec limit trip.Most time the
sec limit would onlt trip if the unit power was turn off
while the hx was still hot.

Turn off power and take us thru the squence all over again
and let us know if the burner try or if the fan come on
as soon as you turn on the power.

nick_8

Sequence

When i throw the switch there are a few clicks, then the combustion air inducer fan spins a few times then stops. Then the main blower engages blowing cold air throughout the house. I found the main limit switch. It was in the lower blower pannel attached to the blower acces pannel( i followed the blue wire from the limit switch to this spot. The switch doesnt apear to be blown but let me describe it. It is a black vertical switch. the top side is pushed in and the bottom is poping out. the bottom portion seems to have a ridge to you from pushing it down(I guess) The secondary limit swictch i am still trying to follow the other blue wire to but the filter was very very dirty especially to the side closest to the blower. I think we are close thanks to all your help. thank you all again

nick_8

Second Blue wire???????

The first blue wire runs from the limit switch to behind the blower. do i have to take off the whole body??

nick_8

wireing Diagram

here is a picture to help with the info. The wire is are labeled and drawn exactly how they run in the box. I hope this helps

nick_8

secondary switch......

I followed the wires by laying down. then run behind the blower then up into it. should this be where that switch is at. If so i will take off back cover and investigate.