You gotta respect this troubleshooting log - http://www.hvacmechanic.com/ Forums
Original message
| justice
 |  "You gotta respect this troubleshooting log"
, posted Sat 9 Feb 23:01  
OK I still need your generous help please - you see I'm really at my wit's end here. And I still can't get a furnace guy until next week. The flame would not ignite anymore after ever 30 clicks. So I got on the roof and got a sweep - swept the soot down the chimney into a shop-vac plumbed outside - i verified the air intake was also indeed free and clear with a mirror - i then sucked up all the soot from the top of the furnace heat exchanger that i could get at - blew compressed air down out through the heat exchanger to the combustion chamber below with the shop vac waiting there to evacuate the soot there -I verified the heat exchanger got a good vacuum seal too. I also wiped clean the LP orifice.
next i pulled off the blower and its face plate and to my shock found that the insulation wrap on inside of the furnace had been pushed down by a careless furnace/duct cleaner man years earlier covering a good 30-40% of the top of my combustion chamber.(that explains the aggressive scratch marks all over the insulation and my high propane bill thank God) Fixed this (wasn't me) damaged insulation foil with some proper foil tape - I also used a mirror to inspect the combustion chamber's top from inside. everything looked good and finally very clean. the only thing I could not do was actually remove the whole unit to get into the four individual heat exchanger pipes themselves.
after replacing the igniter that I may have arced out at the beginning with some over zealous tap tap tapping – still no go. I even bought a new 2nd replacement igniter after I was chastised for touching the sacred element on the first one. I got disheartened when it failed to start the igniter even though a definite click came from the control board. So I think I verified indeed that both igniter's worked by manually wiring them 120v and by plugging them in from 15ft. away just in case :) So then i educated myself with this amazing web about $30 switches and verified the contacts on my old 24V coil double throw read the same as my new one.
Then after I was finally forced to – I found 1 of 3 remaining $200 M1M controller units left in central Alberta
i swear i phoned all day – you guys really shouldn't switch the numbers on them units and keep that info in your exclusive books you know – it's not like the Nordyne man can't afford it and all* Someday all us self-empowered web-monkeys will take rise up against the likes of you stifflers and eat your first-born you know.<---See – I'm ranting – it's called low-level CO exposure here guys – MONOXYGEN.<----Help me.
When I went to swap the Controller out – i found that my igniter arcing incident had actually blown a strip of 120 conductor off the back of my old controller board so yup – i even hacked up a wire bypass soldered to the two affected terminals choosing to keep the new one for spare parts. So I fired it up and to no suprise – flawless cycling and a glorious blue-orange (not yellow-orange) flame. I had my wife pick up a CO/LP/NG detector and for 4 days we have had a toasty home ---->UNTIL TODAY.
Code 4 Flame Failure Lockout again . So begrudgingly I put the new Control Board in there - to no help whatsoever either. I popped the pipes from the top and found the sides of the top of the exchanger are sooting up again. Now this stronger flame won't stay on versus in the beginning it had a weak flame.
I appreciate and took direction from here that it was a combustion issue most likely air – I've pretty much proven my ability to act accordingly with your advice here and now I'm offering a guess that its 1 of two things – a faulty gas valve or a temporarily unblocked heat exchanger manifold(s) that are now being restricted again.
Im opting for gas valve malfunction for 2 reasons (past few years it has been over actuating at start up due to poor air conditions) but im also worried that's due to a couple heat-exchanger manifolds being blocked somehow due to that sloughed off insulative wrap. Is the solution nothing short of a full-blown furnace colonoscopy here?
I verified 45% tank volume and 11 pounds line pressure. And FWIW i did hear that furnace gas valve whistling at actuation earlier today - but i attributed that to -30 - not imminent failure.
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Replies:
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| justice
| "Re(1):You gotta respect this troubleshooting" , posted Wed 22 Oct 23:44
Just a follow up on what was wrong with the furnace. After 2 ignitors and a new controller didn't fix and all multi-meter readings didn't seem wrong - I was completely troubleshot to my wits end.
With a 2 to 3 week wait for a furnace guy in desperation I removed the blower assembly and found all the scratch evidence needed to conclude that the insulation wrap had been carelessly poked and pushed down to cover at least 1/3 of the heat exchanger by an overzealous "furnace and duct cleaning" serviceman.
I completely vacuumed out the heat exchanger vacuum sealed from the base and I blew compressed air down inside from the top of the unit (Warning: exhaust your shop vac through a drywall air-filter OUTSIDE your home and seal any entry points for that nasty soot - before you begin)
After confirming the heat-exchanger was clean - i put it all back together and fired it up. It all worked flawlessly with a bright blue-orange flame. To confirm my fix was the source of the elusive problem - I had previously used $700 in 30-40 days and this last top up finished the winter and I still have $200 in the tank 9 months later.
PS- If your replacing the ignitor with a universal one - make sure to measure the gap between it and the burner or it may arc out on you and cost you a new controller. PSS- You can resolder a wire onto the backside of your blown controller to bridge any missing conductor - Yup - I truly hacked my furnace - but I am so much better prepared for next time by doing so. thx
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| static
| "Re(1):You gotta respect this troubleshooting " , posted Sat 9 Feb 23:10
Got a volt meter?
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| | justice
| "Re(2):You gotta respect this troubleshooting" , posted Sat 9 Feb 23:24
I can run to the shop and get one - why?
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| | static
| "Re(3):You gotta respect this troubleshooting" , posted Sun 10 Feb 01:46
You'll need to verify that the gas valve and all controls leading up to it are receiving and passing voltage.
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| | justice
| "Re(4):You gotta respect this troubleshooting" , posted Sun 10 Feb 13:27
This makes sense - but im not sure what terminals you feel I should be measuring at what time. would it be best to post a pic some how?
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| | marchvac
| "Re(4):You gotta respect this troubleshooting" , posted Sun 10 Feb 08:48
You should also verify manifold pressure. If this is propane like I think it is, you should have 11" of gas to the valve and 10" after the valve. In my opinion those tank gages are only good for plugging a hole. If the propane is not burning corectly then it will soot up quickly. It will also make your flame sensor dirty.
Be careful sometimes you don't get a second chance
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| | justice
| "Re(5):You gotta respect this troubleshooting" , posted Sun 10 Feb 13:21
Thanks- Ive often wondered if the propane delivery from the tank to the trailer itself was to blame. So do you use a manometer to verify line pressure both before/after the gas valve? If the propane vendor does come out to verify line pressure - doesn't he only check up to the valve on the exterior of my trailer?
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| | tom446
| "Re(4):You gotta respect this troubleshooting" , posted Sun 10 Feb 08:47
Is this a mobile home unit ?
If in doubt call a pro !
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| | justice
| "Re(5):You gotta respect this troubleshooting" , posted Sun 10 Feb 13:28
Yes it's a 1999 mobile home with a 1998 model Intertherm furnace.
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| | tom446
| "Re(6):You gotta respect this troubleshooting" , posted Sun 10 Feb 17:26
Sooting is caused from incomplete combustion. As Marchvac says one thing that can cause it is gas pressure. You should see 11 in. w.c. coming into the valve. Most gas valves in mobile home equiptment are non adjustable. They have 2 settings... Natural gas or LP. When set for LP, Manifold pressure will normally run 9 1/2 to 10 in.w.c. If incoming pressure is ok and the manifold is not, the only fix is to replace the gas valve,
Lack of primary air is another frequent cause for sooting. I believe your furnace has a double pipe going to the roof, The inner pipe is the exhaust and the outer pipe is the primary air for the burner. Pull the cap off the chimney and inspect the inner pipe, I find a dozen or so per year where a hole or some pinholes rot through the exhaust pipe. When this happens the burners pull exhaust fumes back to the burner rather than air from outside. Exhaust fumes has no oxygen which the fire needs and results in sooting.
Another cause of sooting is crack in heat exchanger.
If in doubt call a pro !
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