Friend has furnace problems

Messages
968
Location
Battle Creek, MI
A buddy of mine has been battling problems with a furnace not lighting and has figured a way around it (safely) and a repairman has been out 3 times but still not 100% fixed. It's a Payne 74k BTU furnace from 2002, not sure of the exact model. It is a condensing style furnace. What happens is he will turn it on from the thermostat, starts up and works fine. On the next cycle it will not light, tries three times, then won't try anymore. He can turn the furnace off and restart it and works fine for one cycle, then back to the same problem. The service technician has replaced the ignitor and cleaned the flame detector. My buddy has vacuumed the condensate lines and has made sure the P trap is full of water. Voltages from the circuit board were also checked. Based on some research my buddy thought maybe there wasn't enough air for combustion and removed a side panel and now the furnace starts up every cycle. The flame burns a lot stronger and air coming out of the vents is warmer. On the last trip from the technician they both inspected the air inlet pipe from outside the house and couldn't find any blockages. He thinks that maybe the inlet pipe is undersized, which is 2". I found a sizing chart for another brand and 2" seems to be plenty big for a 74k BTU unit. Any ideas on what the problem is? My only thoughts are either there is still a partially blocked inlet pipe or maybe the blower motor is a little weak.
 
Messages
1,281
Location
canada
the inducer motor may be going on it, does the furnace not throw and error code, there are many safety shut offs on these furnaces i suspect one or more are coming in to play to lock out ignition.
 
Messages
2,806
Location
Michigan
Check draw on the air supply motor (inducer motor??? not sure of the term sorry). Check for physical restrictions on the air intake, my neighbor had snow bank covering his and furnace would not light.
 

SVTCobra

Thread starter
Messages
968
Location
Battle Creek, MI
Only codes are 34 and then 14 [Linked Image] Earlier post I said blower motor, referring to the inducer motor that pulls fresh air in and exhausts out the combustion gases.
 
Messages
1,281
Location
canada
hopefully the tech did all the required trouble shooting but from what your saying i don't think he tested to much ,( pretty hard to fix a problem over the internet ) A good tech should have been able to fix this on the first visit. First clue for me on questioning the techs abilities ( not knowing that two inch pipe was the proper vent size ..)
 
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Messages
440
Location
Peace valley, Missouri
Igniter board locks out after three tries thats normal. The red light flashing on board is the fault code. Flame rod/ sensor should be replaced also check pressure switch tubing for water in the from condensate. We need the code.
 
Messages
2,304
Location
Seattle-ish, WA
We had a very similar problem (almost the same IIRC) a few years ago. As mentioned, Inducer motor. Usually one of the first suspects here; would have expected a tech to address that.
 
Messages
3,173
Location
USA
First the inducer fan comes on which alters the pressure in the burner chamber, closing the pressure switch. If that does not work, you get a code 31 not a code 34. Once the inducer proves OK it then goes to the ignition phase. Code 34 means that the initial "pilot" flame did not light off, or it did but the flame was not detected. That is often an airflow problem but also look at general cleanliness and the ignition and flame detection systems. There is usually a view port where you can watch the flame to differentiate the problem between not lighting and not detecting. If the intake pipe is very long, the diameter might need to be increased. That would be in the installation instructions.
 
Messages
171
Location
NV
I had this problem on a newly installed Bryant unit once. Only occurred intermittently. After replacing numerous components, local heat and cool called upon Carrier Corp. ace troubleshooter. He pegged it as an bad ground. Sure enough, he was right. Ground wire in subpanel had never been properly tightened.
 

SVTCobra

Thread starter
Messages
968
Location
Battle Creek, MI
Originally Posted by mk378
First the inducer fan comes on which alters the pressure in the burner chamber, closing the pressure switch. If that does not work, you get a code 31 not a code 34. Once the inducer proves OK it then goes to the ignition phase. Code 34 means that the initial "pilot" flame did not light off, or it did but the flame was not detected. That is often an airflow problem but also look at general cleanliness and the ignition and flame detection systems. There is usually a view port where you can watch the flame to differentiate the problem between not lighting and not detecting. If the intake pipe is very long, the diameter might need to be increased. That would be in the installation instructions.
That's where the tech left my buddy to research the installation instructions. He thinks it's too small of an inlet pipe at 2" diameter. Only thing that puzzles me is it's been working for 17 years in it's current setup.
 

SVTCobra

Thread starter
Messages
968
Location
Battle Creek, MI
Buddy found the installation manual and the inlet ducting is installed properly. He has a run of less than 30 feet and three elbows. 35' is the max for an 80k BTU unit and 2" piping. [Linked Image]
 
Messages
6,101
Location
Texas Hill Country
Me being a non furnace tech, would throw a flame sensor and a hot surface igniter at it. They are both dirt cheap parts and easy for the DIY to install. I have done both these parts in a few furnace apartments when I owned rental properties, I think they are 40 bucks in parts for both.
 
Messages
7,421
Location
California
My parents had something similar happen to their Trane XV95 that was made in 2010 - it was parts cannnoned by the same HVAC company who installed it and the problem was mostly the control board. Same symptoms - the furnace would go through its startup routine by kicking on the inducer motor and ignition sequence only to shut down a minute later. Check the igniter to see if it's not broken or burned out, check the flame sensor. See if the inducer motor spins healthy without shorts in the windings(easy to check with a DMM set on the ohms scale, you should get continuity).
 

SVTCobra

Thread starter
Messages
968
Location
Battle Creek, MI
He has it rigged up now where the inlet pipe has a Y, one pipe is the inlet and goes outside of the house, the other side terminated in his mechanical room with a cap. He took the cap off and reinstalled the side panel and everything is good. He has also run a plumber snake through the inlet pipe and found nothing. Since it runs fine with the cap off and has the right size inlet pipe according to the manufacturer's installation manual there is a restriction somewhere. Neither a visual inspection nor a plumber's snake has found it though.
 
The inducer motor has to work harder to pull air through the longer pipe and elbows. Any way to check it under load? What about trying a shop vac from both ends of the inlet pipe instead of a snake? You could try vacuum and blowing through it.
 
Messages
342
Location
Michigan
Feel inside of the inlet pipe. The exact right conditions of cold/humidity/snow can cause a thin layer of ice to form just inside the inlet pipe. It may not be easily noticeable but can narrow the diameter of the pipe just enough to cause inadequate air flow. This happened to me once in 22 years in the same house.
 
Messages
7,980
Location
MI
When I re-read all of SVTCobra's description of symptoms, is sure does seem like maybe he has a "tired" inducer motor that is giving intermittent problems based on how long it operates (warms up, bearing or brushes affected?). The fact that the furnace runs o.k. when he opens up the air inlets also seems to be very telling (less load on the inducer motor)... the ice buildup just mentioned or some other odd restriction? If not that, maybe the control board is malfunctioning and not reading the sensors correctly? Don't ignore the simple things like the ground wire mentioned above - maybe the warming/cooling is affecting contact . Sometimes we miss the obvious. I just helped my son replace his Goodman inducer motor. $180 through Johnstone and about $325 through an appliance repair shop. $150 +/- seems average at online vendors.
 
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