Amatuer's logical troubleshoot sequence on "no heat" in legacy heaters


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Old 10-21-14, 03:39 PM
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Amatuer's logical troubleshoot sequence on "no heat" in legacy heaters

I am writing this to share a light to all who lost heat and just wonder what to do before calling 200 bucks for hearing "You need a new xxx" tech saying.

I am a total dumb and still dumber in heating business, who just spent 2 tweeks troubleshooting my old hog, "York Stellar Plus" gas furnace and learned few that I decided not to buy new one, every service companies I called eagerly tried to convince me to do.
So I may be deadly wrong but I just want to share with others and will to learn more. Welcome any comments and corrections.

My furnace now runs like a champ.
Saved 3.5 grands.

So, here we go.

Assumptions:
Circuit breaker is on
Furnace switch is on( if there)
Fuse(if there) is good
Thermostat is good and temp is setup at higher than you have now.
Thermostat's "Fan" switch is at "Auto".

Terminology:
Ventor motor: Commonly mixed with draft, inducer, blower(not correct), Not fan motor definitely! This is a motor sits right in front of you when you uncover the main front panel, with some tubings going in and out.
Fan motor: mixedly used with "blower". This is mostly hidden below or behind the unit.
Circulates the air via the property air ducts.

The most important thing in troubleshooting is analyzing...
"The Sequence!"of accidents.

Of what you see/hear on your unit from the moment you power on the heater.
Follow below going down the sequences if your answer is "Yes" to each steps.

1. Power On/Thermostat heater on: Meaning just you switch to "Heat"
2. Does ventor motor start(You can hear and see)? No
3. After few secs, does ignitor glows(see through windows)? No
4. After few secs, is there s "click" sound? No
5. Does burner fires up? No
6. Does burner fire stays on for at least few minutes? No
7. Is burner fire color in pure blue? No
8. Does burner & ventor motor stops at temp reached as thermostat set at? No
9. Does fans stop after few minutes after burner & ventor stopped? No
10. Does ventor start at next heat cycle? No
11. If your are here, I think you have a working heater!

In this post, I will tell my learnings on setp 2.
I will follow up all the rests one by one later, if welcome.
Opposite "No" follow down rule applies.

2. Ventor motor doesn't start/run at all:
1) Pressure switch shuts the circuit.
Against your imagination, the prseeure switch is NOT governed by "controller" at all. It just does its own by itself.
Main pressure switch may open the circiut between C(common) and NC.
Do not jump on the gun blowing the air tube with your mouth. Do not blame the pressure switch at this point at all. Pressure switch fails if something else fails for your safety. If something is not right, shutting down is its job! So,

a) See if there is water building or any sorts of blockings in all tubings by taking all out and clean them, just tubes, not the pressure switches! Better to know it needs nearly vaccum state within the tubings.
Restart heater and does it start? Yes

b) At this point, you must broaden your thought about air vent/flow domain.
Look at your filter, open and check dirts build ups in blower motor fins, vent pan, ventor motor and the filter. Just vaccume all these and replace/clean filter: Needs some real works here, no jokes.
Restart heater and does it work? Yes

c) Here, you need a multi/volt meter.
While the system is on, check the low voltage(AC) on the "transformer", between "C" and "heat (W mostly)" terminal.
Do you read constant 24+ VAC? If Yes, go to e)

d) The culprit is transformer, get a new one!
If this fails, NOTHING works!

e) OK, 24 VAC is hot via transformer but the pressure switch still close for still some reason(s). But still keep in mind that pressure switch is a "safety monitoring system, may not be the root cause!".
Get or make a jumper cable and connect on pressure switch between "C" and "NC" terminal, with existing connection in tact.
Restart system, does it start? Yes

f) Reluctantly consider replacing the pressure switch...

I will follow up the rest if welcome.
 
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Old 10-22-14, 12:28 AM
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Welcome to the forums.

These are the repair forums. We appreciate your blog but we try to address specific problems here. You seem to have an idea what you are doing but someone following along may be confused.

f) Reluctantly consider replacing the pressure switch...
Yes... be very reluctant as pressure switches very rarely go bad. The pressure switch is an indicator of a problem somewhere else.
 
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Old 10-22-14, 06:27 AM
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Oops. My bad.
Newbie's mistake.
 
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Old 10-22-14, 10:52 PM
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No harm..... no foul.

If you need any help or have a question.... please feel free to ask.
 
 

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