Greetings all. Homeowner learning by research here. I had this furnace stop working properly about a three and a half weeks ago. Thank goodness SE MN is having a relatively mild winter
I'm poking around with it because I like to learn things and I'm just competitive, stubborn, and cheap enough to want to keep going. My skill set revolves around computers, software development and general 'trouble shooting' (sometimes making).
I knew of a few things at the start: 1. the furnace is old (orig install date 12/4/2000). 2. the blower fan had not worked for years (house still heated just fine so I never worried about it). 3. I was never good at changing air filter in a timely manner.
The original problem was that the furnace 'just went out' (of course the day before I left for a week on business). I got home and did the 'normal' operational reset (furnace off, gas off, internal gas switch off, flip breaker to off, turn thermostat off and set it as low as possible). Then turn it all back on and make a call for heat from the Thermostat.
I wasn't aware of the standard startup process, but as I know now..it started as it should. It then ran for about 30-45 minutes and shut down. It threw a code 13. Research showed to check filter. (oh-oh...yup, dirty and changed with 'more expensive' type). Did reset. Ran for awhile and died again with a code 13. Read some more here and found that the ole gal doesn't like those fancy filters so went out and bought another one that looked like the old blue one I removed. Still same issue. So the hunt was on, it wasn't going to be a super simple fix.
What has been done since then: (probably more than this but these are the major areas) ALL with power off and break off (I like to be alive)
- made sure vents were cleared
- checked the white drain (had to clean that previously to make it run)
- made sure the inducer motor was running well
- made sure the hose going into the inducer motor was clear of obstruction
- Reset the rollout switch (ah-ha! found it. Nope. Still getting thrown)
So the thought is now that it's not necessarily a 'breathing' problem, it's getting too hot. Reset switch and restarted everything again. Watched the flame to see if it was bright blue, conical in shape, and wasn't 'blowing back'. All looked good for me. I had some small orange flame between the cones for flashes but not a lot. Nothing looked like the flames were out of control or rolling around or backwards. The 'flame box' felt hot to me when I touched it . Not so hot that I couldn't hold fingers on it for a couple of seconds. But it was warm, pretty warm. Nothing seem discolored on the outside and one of the suggestions was to open the front and see if you could feel the flames coming back at you. They were quite excessive in the videos I watched. Nothing like that for me. The orange flames did happen a bit more frequently like this though. Started thinking that the blower fan should really be pushing some of this heat upstairs instead so found the squirrel fan, motor, and capacitor online and got them installed.
Tested again, fan came on right away, then the inducer fan, then it started. It ran for about an hour then code 13 and shutdown. At this point I did a reset. I left the cover off this time so I could watch it die (I'm an optimist). It didn't. Watched for 15, then 30, then 50. Then I went upstairs, leaving the front cover of furnace off). It ran for about 2 hours and shut off. It never hit the temp that was called for by the thermostat so I went down to inspect. A code 33. More research.
Things that were tried since then:
- use wood match with gas turned off but fan and inducer running to check for any blow back (I guess flame should dance or go out if there is a big enough hole in the secondary heat exchanger)
- cleaned the top and bottom of the a-coil, it was 1/2 covered with "hair"
- checked the continuity of the heat switch (forget it's name...white and to the left of the top part of furnace..not flame sensor or rollout switch, but connected to rollout switch I think)
- Noticed that blower fan didn't shut off when the furnace went into error code.
- Still wonder why the furnace can't heat home to anything over 68 degrees any longer. (That's where I've kept it every winter for four years so maybe 'trained')
- Noticed that the '2nd stage burn' wasn't happening any longer. I thought I always heard the 'after burners' come on and then was observing through the peep hole while the jets were turned up (or at least I perceived them to be).
- No obnoxious odors (gas, whatever comes when secondary heat exchanger has cracks - saw that in a couple videos; checked by furnace, up on first floor, and outside by vents).
- System has decent airflow at the outdoor vents. I know there is air moving, one for sure out, the other feels like a soft vacuum but not enough to stop you from pulling your hand down if you want to take it off.
Still throwing a code 13 then 33 (or vice-versa...I forget now)
Decided to look at filter again and noted that the flimsy cover that went over the top seemed 'warped' a bit. Picked it up while the furnace was blowing cold air and pulled the filter away from blower fan and let go and it got drawn right back quickly. I replaced the cover and set something heavy on top of it as I seem to recall fitting more snugly in the past.
Did the reset procedure. This time I was locked out. The furnace gave me a code 14 and I think it ended with a 34 (that's a lot of flashes to keep track of! Especially when triple checking that you counted correctly).
So, no ignition. So tonight try with a fresh reset and see if I still get the 13/33 code or do I now get the 14/34 combo. I can't believe setting a weight on the cover would have that affect?
So, my bet is that I'm going to get a 13/33 combo meaning heat again. My next step if it is heat is to replace the flame rollout switch and that temp sensor thing...maybe covered with some of that dog hair/lint/whatever that was on the bottom of the a-coil when the filter was not doing its job.
Questions I hope you can help me with given the background:
1. From most of what I've read and watched, I can't believe the flame rollout switch is failing itself. Is that even possible? Can it get so hot, without leaving any scorch marks inside or outside, that it just randomly fails?
2. I don't want to tear the middle of the furnace out to look at the Secondary heat exchanger if I don't have to. I do have an endoscope for my phone that I may send in for a peek. Look for rust, holes, cracks etc? Should it be pristine in something that old or is okay with small patches of rust?
3. Trying to find a rental for a C02 tester to see if there is the proper mix heading out. Those little puppies are expensive! Pro tools usually are though.
4. Do you think the 14/34 could have been thrown because I didn't go upstairs and turn off thermostat and turn heat all the way down before resetting the furnace?
I'd appreciate any other ideas/tips as well. Thank you.