This is Just Weird - Lennox Gas Heater

[Edjamacator]

I've looked for help on other posts, but haven't found anyone with the
same symptoms.

Hopefully someone can help me out. I'd appreciate it if you could.

Anyway, I have a Lennox G51MP gas furnace converted to LP gas. It's about
eight years old. Since last winter, it will sometimes kick on and work and
other times (which accounts for most of the time) won't. It tries 5 times
and then goes into Watchguard mode.

Here's what happens: The "first" burner all the way to the right where the
hot surface igniter is will come on, push out a blue flame, and then turn
off a few seconds later. There is a "click" when this occurs. Neither of
the other two burners come on. This is attempted five times and then
Watchguard mode is on for an hour.

When it does work, which is the weird part, it looks like the "first"
burner isn't on, but the other two are burning brightly. The flame sensor
is red hot and heat actually comes out of the vents. The furnace stays on
when this occurs.

Now, I've emptied the condensate trap, replaced the surface igniter
(without touching it with my skin), and tried it with the burner box lid
(where the little circular window is) off. It still acts the same way. In
fact, it came on right before I emptied the condensate but not after, and
this was all after replacing the igniter. Nothing I've done seems to alter
its cycle of sometimes working, sometimes not.

If something was clogged, wouldn't it always clog? I can't figure out why
burners would sometimes work and then not the other times, and why the
"first" one would appear NOT to work when the others do, seeing as how the
igniter is in front of that one. I tried taking off the top cap to try and
remove the burners for cleaning, but it doesn't appear to come off. I can
rock it side to side with the screws removed, but I don't want to put a
bunch of force on it to take it off. Maybe it's just jammed? It looks like
it should be able to slide off.

Sorry so long, but I wanted to make sure as many details were present as I
could provide. If anyone has any ideas, I'd love to hear them. Thanks.

[j***@gmail.com]

Post by Edjamacator
I've looked for help on other posts, but haven't found anyone with the
same symptoms.
Hopefully someone can help me out. I'd appreciate it if you could.
Anyway, I have a Lennox G51MP gas furnace converted to LP gas. It's about
eight years old. Since last winter, it will sometimes kick on and work and
other times (which accounts for most of the time) won't. It tries 5 times
and then goes into Watchguard mode.
Here's what happens: The "first" burner all the way to the right where the
hot surface igniter is will come on, push out a blue flame, and then turn
off a few seconds later. There is a "click" when this occurs. Neither of
the other two burners come on. This is attempted five times and then
Watchguard mode is on for an hour.
When it does work, which is the weird part, it looks like the "first"
burner isn't on, but the other two are burning brightly. The flame sensor
is red hot and heat actually comes out of the vents. The furnace stays on
when this occurs.
Now, I've emptied the condensate trap, replaced the surface igniter
(without touching it with my skin), and tried it with the burner box lid
(where the little circular window is) off. It still acts the same way. In
fact, it came on right before I emptied the condensate but not after, and
this was all after replacing the igniter. Nothing I've done seems to alter
its cycle of sometimes working, sometimes not.
If something was clogged, wouldn't it always clog? I can't figure out why
burners would sometimes work and then not the other times, and why the
"first" one would appear NOT to work when the others do, seeing as how the
igniter is in front of that one. I tried taking off the top cap to try and
remove the burners for cleaning, but it doesn't appear to come off. I can
rock it side to side with the screws removed, but I don't want to put a
bunch of force on it to take it off. Maybe it's just jammed? It looks like
it should be able to slide off.
Sorry so long, but I wanted to make sure as many details were present as I
could provide. If anyone has any ideas, I'd love to hear them. Thanks.
--
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Normally the burners are arranged so that once the first one lights it ignites the rest of them. Typically that's a mechanical flame path. Look for that and make sure it's in the gas/air stream. Inconsistent is not that surprising. Sometimes the subsequent burners are igniting before the flame sensor shuts it down and sometimes they aren't. I'm skeptical about the first burner really being out. Watch it with the lights off, it's easier to see the flame and flame travel in the dark. It's remotely possible that a delay in igniting the subsequent burners is causing a small "explosion" when they do ignite that is blowing out the first one. That would be a pretty dangerous situation as you then have unburned gas entering the exhaust stream. It's fortunate it's a high efficiency as it's less likely to ignite in the exhaust. Still a really bad thing.

The burners usually all remove as a unit and typically you have to take off some other stuff to get them out. Possibly including the gas valve. That's usually reasonably obvious if you look it over. If it's not (nothing personal) maybe you shouldn't be working on it. Gas furnaces are not exactly the best thing to repair via trial and error.

Sounds like you really need to observe the burners going through the cycle a few times to really see what's going on. Again, low light helps.

[Tony Hwang]

Post by Edjamacator
I've looked for help on other posts, but haven't found anyone with the
same symptoms.
Hopefully someone can help me out. I'd appreciate it if you could.
Anyway, I have a Lennox G51MP gas furnace converted to LP gas. It's about
eight years old. Since last winter, it will sometimes kick on and work and
other times (which accounts for most of the time) won't. It tries 5 times
and then goes into Watchguard mode.
Here's what happens: The "first" burner all the way to the right where the
hot surface igniter is will come on, push out a blue flame, and then turn
off a few seconds later. There is a "click" when this occurs. Neither of
the other two burners come on. This is attempted five times and then
Watchguard mode is on for an hour.
When it does work, which is the weird part, it looks like the "first"
burner isn't on, but the other two are burning brightly. The flame sensor
is red hot and heat actually comes out of the vents. The furnace stays on
when this occurs.
Now, I've emptied the condensate trap, replaced the surface igniter
(without touching it with my skin), and tried it with the burner box lid
(where the little circular window is) off. It still acts the same way. In
fact, it came on right before I emptied the condensate but not after, and
this was all after replacing the igniter. Nothing I've done seems to alter
its cycle of sometimes working, sometimes not.
If something was clogged, wouldn't it always clog? I can't figure out why
burners would sometimes work and then not the other times, and why the
"first" one would appear NOT to work when the others do, seeing as how the
igniter is in front of that one. I tried taking off the top cap to try and
remove the burners for cleaning, but it doesn't appear to come off. I can
rock it side to side with the screws removed, but I don't want to put a
bunch of force on it to take it off. Maybe it's just jammed? It looks like
it should be able to slide off.
Sorry so long, but I wanted to make sure as many details were present as I
could provide. If anyone has any ideas, I'd love to hear them. Thanks.

Hi,
Logical sequence is after burner lights up - flame sensor - blower fan
and so on. Flame sensor rarely goes bad, just wipe it clean with emery
cloth or fine sand paper gently. Burner is coming on and how come
ignitor is replaced? No trouble code?

[Congoleum Breckenridge]

Post by Edjamacator
I've looked for help on other posts, but haven't found anyone with the
same symptoms.
Hopefully someone can help me out. I'd appreciate it if you could.

Have you read this:
http://0190acd.netsolhost.com/manuals/G51MP_Series.pdf

[Greg mrg]

I really hope that you still use an email associated with this account and somehow you will get notification about my response. I registered here hopping that you found a solution for your problem and you could share it with me. I am having same issue (with exception of having the right burner not working properly) and this is the only similar case I found all over the internet. It takes 3-4 times for my G51MP to properly ignite all burners. Only the right one usually starts (and then of course shutdowns right away because the flame sensor is on the far left one) . Sometimes it just gives up after 5 times.
I had the burner replaced, sensor cleaned, gas valve replaced ... I am starting to think that there is too much air sucked in and it blows the gas away ... I am clueless and so are the 2 technicians I had here

[Tekkie©]

On Tue, 13 Oct 2020 20:15:02 +0000, Greg mrg posted for all of us to digest...

I really hope that you still use an email associated with this account and somehow you will get notification about my response. I registered here hopping that you found a solution for your problem and you could share it with me. I am having same issue (with exception of having the right burner not working properly) and this is the only similar case I found all over the internet. It takes 3-4 times for my G51MP to properly ignite all burners. Only the right one usually >
starts (and then of course shutdowns right away because the flame sensor is on the far left one) . Sometimes it just gives up after 5 times.
I had the burner replaced, sensor cleaned, gas valve replaced ... I am starting to think that there is too much air sucked in and it blows the gas away ... I am clueless and so are the 2 technicians I had here.

Did they clean the orifices? Roll out switch?