Any HVAC techs out there? Gas furnace help please...

Jody Treadway

Jody Treadway

Croc wearing fool
Moderator
Joined
Mar 20, 2005
Location
Hendersonville, NC
Of course it's supposed to be 23 here tonight and the gas furnace crapped out. Our remote controlled gas log solenoid failed last month so I need a little help here!

2002ish gas furnace, fan runs but no heat. The inducer motor works and there is exhaust out of the side exit of the unit. I get a code 4, pressure switch stuck open code.

I tested the following:
tube from inducer to pressure switch is good, no holes and not clogged
inducer "nipple" is not clogged all the way into the inducer housing
the pressure switch "clicks" when vacuum is applied
The thermostat in the house is set high enough to turn the unit on

Same thing happened earlier this year (January) and I replaced the pressure switch and it has worked fine ever since. Until tonight.

I wonder if I got a crappy switch or if something else is causing it?



IMG_20141102_173858_970.jpg
 
Our pressure switch crapped out last year too, if I remember correctly (and this is 10 months of cobwebs so maybe not) I confirmed it by jumpering past the switch, essentially hot-wiring it.
 
Did you put a continuity meter on the switch and put vacuum to it/suck on the nipple? Is it getting voltage when the heater is on? Probably 12 or 24v. Did you try hitting it?
 
If u do not have a meter yes you can just jump the two wires together to test. I would not recommend leaving this way, cause if inducer was to fail unit wouldn't know and could possibly fill heat exchanger with gas and then if it lit could go boom. But if you know inducer working be a good way to test and to run a little to get house warm.
 
DVOM is at the shop...not much help there.

I tapped on the switch with no change. I'm about to go out and jump it with a paper clip and see what happens.
 
Check for blocked flue pipe. If pvc flue pipe check hoses off bottom of inducer, could be full of water or froze. Check drain trap coming off inducer could be stopped up or froze also. If metal flue then water problems don't apply.
 
braxton357 said:
I have a pullout sofa and a pair of snuggies if you two get too cold.
Click to expand...

Dude you better jump on this offer
(regardless of the turnout on the switch)
 
Nope...
New pressure switch (warranted from January), removed inducer, thoroughly cleaned the flue, new hose, verified the circuitry is good. Appears to be a bad circuit board.
Reinforcements have been called in and they'll be at the house at 4 to diagnose.

Talked to Rory last night BTW. Thank you for having him call me.
 
Thought I'd update this since it is way too cold to be in the shop today!

After a ton of head scratching, I found out the manual that I *thought* was for my furnace was for the ORIGINAL furnace and as such the code numbers didn't match up.
My code 4 indicated an ignition failure. I tested the ignitor and found it to be open. Replaced it and good to go.
Big thanks to @sammi_davis for having his bro in law (HVAC tech) call me. I appreciate that
 
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