Diagnosing gas furnace

[Oro_O]

The temps were unseasonably low last night, and mama bear turned on the Gas furnace last night because one little cub had some sniffles. No go, nothing at all.

I have spent time trying to sort it out. It worked when last used in the spring. It is entirely dead and no response at all. There is 120v to the control board inside the unit (pic below, via the lowest black wire on the left side of the board.). I thought if you jumpered the red and white wires from the controller, it would switch on? There is a error code button (middle bottom) that is supposed to flash error codes or an "ok" code via light above, but nothing happens when pushing it.

It is a York, nine years old. I last touched it two years ago replacing the inducer motor and cleaning the igniter rods. Has worked perfectly since then until it would not respond last night. I can't find good diagnostic references online.

How can I test the thermostat vs board to ID which is bad? The thermostat is a commn Honeywell, th4110d1007.

 

[dbias]

is the fuse on the top right side of the board good?

 

[Astro14]

Edit - You're certain that it's getting 110v?

 

[Oro_O]

Good point! Yes, it is intact.

 

[Oro_O]

Originally Posted by Astro14
Edit - You're certain that it's getting 110v?

Yes, my multimeter reads 121.5v at that lowest black lead on the left side if I pull it and probe it. I started at the conduit and checked all the way to there. There is a panel switch in the panel lead so the unit cannot run with the access panel removed, I am aware of that and depressd it when I treid to jumper the thermostat leads.

 

[dbias]

Have you checked the roll out switch?

 

[Oro_O]

No, but I will google that and see. I am not expert with these, and have not run into that before.

Edit: appears OK, it has continuity across the two terminals.

 

[MasterSolenoid]

My Furnace is a Heil / 93% efficient
Installed May 2009

In order for any 'newer' Furnace to work, things have to happen in the proper sequence.

My Furnace:
1) Inducer Motor STARTS @ 0 seconds
2) Ignitor 'glows' @ 24 seconds
3) Gas Burners Turn ON @ 38 seconds
4) Fan comes ON @ 1 minute, 24 seconds
*** House heats up to desired temp
5) Gas Burners Turn OFF @ 6 minutes, 39 seconds
6) Fan shuts OFF @ 8 minutes, 19 seconds

Start at the beginning and determine at what sequence you have failure.
Does the Ignitor 'glow' ?
Do you have Gas Pressure ?
Does the Fan come ON ?

Good luck. Last result you call Repairman.

Edit 1) Does your Thermostat have Batteries ? ? ?
Edit 2) My Furnace stop working once because some 'rust' dropped onto the Ignitor and burned it out.
In diagnostic work, start with thinking SIMPLE. It worked last year, no one touched it and it does not work now.

This may not answer your question, I was just throwing some info out there.

 

[Oro_O]

There is zero response to the thermostat - inducer motor/fan does not come on (it is fairly new - I replaced it). Thermostat has new batteries and r/w/g wires are tight at themostat base and on furnace controller board.

 

[MasterSolenoid]

I think I would purchase another Thermostat and see if that's the problem, because
you say you have power inside the Furnace
and you say "There is a error code button (middle bottom) that is supposed to flash error codes or an "ok" code via light above, but nothing happens when pushing it".

But I'm no expert, I look forward to hearing other solutions.

Let us know how you eventually get it fixed.

 

[zzyzzx]

Try bypassing the thermostat first.

The next thermostat I buy is going to be an ICM Controls one. I really hate Honeywell.

 

[CPB]

Here is your manual: https://climate.emerson.com/documents/50a56-956-instructions-en-us-3583550.pdf See pages 7 & 8 for LED codes.

 

[emmett442]

Originally Posted by zzyzzx
Try bypassing the thermostat first.


He did, by jumping the red/whi wires.

You have 120v at the furnace but those are only for the load side of the board's relays to power the equipment (like the induction and blower motors). Control runs on low voltage (24V) supplied by the transformer. Especially since even the error light doesn't respond, I'd start there. Check for voltage from the transformer.

 

[doitmyself]

Do you have a condensate pump and/or float that could be stuck?

Bad pressure switch that controls the inducer motor, dead animal in vent locking inducer fan (happened to me)?

Have you shut off power at your breaker box for a minute or two - possibly reset some type of switch in your control panel ? (you have no green lights at all?).

Diagnostic flowchart: https://arnoldservice.com/wp-content/uploads/2012/12/furnacetroubleshootingflowchart1.jpg

 

[RamFan]

I JUST went through this in my house as well. I used the video below to test the thermostat.

 

[Oro_O]

I have 120v at the black line side wire (lower left) and 26v at the upper right blue load side wire.

Poking around elsewhere, I have 4.4v at the flame sensor, continuity in a switch/sensor above the burners (not sure what it is), and nothing on either of the inducer motor wires.

No drip pan or float.

I apreciate all the help!

 

[Oro_O]

Originally Posted by doitmyself
Do you have a condensate pump and/or float that could be stuck?

Bad pressure switch that controls the inducer motor, dead animal in vent locking inducer fan (happened to me)?

Have you shut off power at your breaker box for a minute or two - possibly reset some type of switch in your control panel ? (you have no green lights at all?).

Diagnostic flowchart: https://arnoldservice.com/wp-content/uploads/2012/12/furnacetroubleshootingflowchart1.jpg


I have flippe the breaker and it has been off a while at times.

Bad switch for inducer motor sounds like a route to check. Tips on how to do that appreciated. Will google and check the flow chart link. Have been looking for a solid diagnostic chart w/o success, everything is superficial. Hope that one helps.

 

[emmett442]

Originally Posted by Or
I have 120v at the black line side wire (lower left) and 26v at the upper right blue load side wire.



OK. Now does the 24V make it to the red t-stat wire?

If not, board is bad. If so, and jumping red/whi seems to do nothing, check for power to the inducer capacitor.

No power to capacitor - board is bad. If power, check inducer motor.

 

[Oro_O]

Yes.

It appears a bad board. If I follow the diagnostic doitmyself posted, that's the call as after that, I have no voltage to the inducer motor on either lead (both are tan). I tried it with the t-stat commanding it as well as jumpering r/w. I have 26v at the red wire at the wall as well as lead on the board.

I checked ed the inducer motor wires and they have continuity, and no v at the board plug for those tan wires.

My suspicion was the board after a little poking (and no diagnostic lights). This helps me feel much better before buying a board.

 

[Oro_O]

Thanks so much!

You know, nine years, and we live in a very temperate climate and the furnace is not heavily used or stressed. Two major breakdowns in that time is not good. To recycle a BITOG specific meme:

York - never again!