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Tempstar pilot not lighting after draft inducer replacement

14K views 53 replies 5 participants last post by  kenmac 
#1 ·
Hello,

furnace: Tempstar NUG9075FGB1 about 13 years old
smart valve: SV9500M 2674

The draft inducer broke so I ordered a new one. The furnace has been off for four days as I was waiting for the new draft inducer to come in and install it.

So I installed it...



I go through the sequence of turning the furnace back on and the pilot won't light. The draft inducer starts, but that's where it ends. No spark or glowing from the igniter.

So I take the cover off to the pilot chamber...



When I start the furnace I can hear the pilot gas coming out after the draft inducer starts. So when I light the pilot manually and put the cover on quickly the flame goes out as if there was too much of a draft or not enough oxygen.:wink:

So my question is...is the igniter supposed to glow to keep the flame going or does it just spark to light it once? If it's supposed to be glowing then that's my problem, but either way I don't see it spark or glow. I'm going to test it with an ohm meter when I get home.

So the furnace has been off for four days and all of a sudden something else is broken...what the hell. :thumbsup:

Thanks for your time,
Dave
 
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#3 ·
Thanks for the reply. Yes I hear the smart valves are actually called dumb valves. I can hear the gas coming out of the pilot pretty good so I think it's ok, but i will clean it.

There is never any sparking or glowing, that i can see, from the igniter.
 
#5 ·
You disturbed the dumb valve when you changed the inducer.
Dumb valves don't like to be disturbed.

It messes up the wire connections, in the molex plug/connector.

Reseat them.

Maybe your dumb valve will forgive you. Some do, some don't.
 
#6 · (Edited)
I tried reseating the connector to no avail.

I did some measurements...

I get 13 Ohms across the igniter (blue wires) so it seems shorted. There is also 0 Volts to the igniter.

I heard the igniter should be around 80 Ohms so it leads me to believe the igniter is bad. The replacement part number is Q3400A 1024.

If indeed the igniter should be low resistance then the valve is not giving voltage. Should be 24v correct?
 
#9 ·
You said you heard gas and lit the pilot by hand that means the valve is passing gas to be lit by the igniter. There is 24 V available if this happens.

Granted, the valve could be operating intermittently, but the igniter would have heated up in the scenario described above.

Possible to have bad valve and igniter? Yeah, but doubtful. You are doing something wrong.


Your furnace has been out for four days; what are you doing for heat?
 
#10 ·
Yes yes I agree that there is 24V to the valve, but the igniter is seeing 0V at all times. I hear some people wedge something between the molex connector to the igniter, but in my case wiggling or reseating the connector does not help. Shouldn't the ignitor see some voltage even if its resistance is higher now?

No heat at all...the house has been a constant 50 degrees...waking up in the morning sucks.
 
#12 · (Edited)
here's a link to help you http://www.fwwebb.com/pdf/htgcat03/2003htgcat_p207-208.pdf

From Honeywell:

AA. - The resistance of a Norton silicon igniter used in the Q3450 or Q 3480 pilot assemblies, when new and cold, will be between 3 and 4 Ohms (average 3.7 Ohms) as the igniter ages the resistance will increase. When its resistance reaches 10 Ohms the igniter should be replaced


You have 13 ohms.
 
#15 · (Edited)
Oh man this troubleshooting is going to go forever haha.

I just checked the control harness voltages and here's the new deal...

24v common to 24v hot = 29V

24v common to 24v thermostat or pressure switch = 0V

So that looks like the problem.

The pressure switch is functioning ok since it closes when the inducer goes on. When the switch is closed I read 29V across it.
 
#18 ·
sounds like it's the ignitor or the electrical portion that feeds power to the ignitor..Like hvclover said .If it were the vaccum/pressure switch you wouldn't have gotten pilot gas.....I hate those dumb valves..Over the years honeywell has made several changes to the valve ..It's still dumb
 
#26 ·
You said this was kindergarten stuff.

I am beginning to think you are deliberately posting misleading info. The inducer would have to be running to check continuity and you did not say that the wire were disconnected. You would have blown the fuse in your meter checking that system live.

Five days no heat.

I am beginning to smell a troll.
 
#28 · (Edited)
It's true no heat since Sunday. The house never got below 49 and I travel a lot so hasn't been a big deal. It's supposed to be 63 today and that is good news. It actually feels colder inside and outside.

Gents, I deal with high speed surface mount electronics hence my kindergarten comment. I still appreciate your help. The only reason I didn't call a pro is because I can get all these parts on Ebay for 1/10th of what a pro would charge me and I could go without heat for a while.

So please help me out man.

I checked the pressure switch with its wires plugged in and not plugged in.

With the wires plugged in:
The switch closes when the induction motor turns on and is open when the induction motor is off.

With wires pulled out:
The pressure switch is open all the time.
 
#31 ·
It's true no heat since Sunday. The house never got below 49 and I travel a lot so hasn't been a big deal. It's supposed to be 63 today and that is good news. It actually feels colder inside and outside.

Gents, I deal with high speed surface mount electronics hence my kindergarten comment. I still appreciate your help. The only reason I didn't call a pro is because I can get all these parts on Ebay for 1/10th of what a pro would charge me.

So please help me out man.

I checked the pressure switch with its wires plugged in and not plugged in.

With the wires plugged in:
The switch closes when the induction motor turns on and is open when the induction motor is off.

With wires pulled out:
The pressure switch is open all the time.
With all due respect I am bowing out of this thread because either one; the guy is tring to prank us. Or two, he does not follow instruction and second guesses the answers given.
 
#42 ·
..knew too much about the system
I will take that as a compliment. Check out my new signature!!!

I will admit I may have been inebriated a few times when posting.

A switch in theory is not supposed to read a voltage across it when closed....I know this, but at the same time it was confusing the hell out of me. See...if I had experience like you guys I would've shorted the switch four days ago.

It is true that you learn more on the job than in school.

Cheers....opens a beer.
 
#50 ·
You seem like a good person hvaclover, someone that cares, as I have noticed here. You took time out of your day to help a fellow human in need and I greatly appreciate your help and everyone that chimed in. If you felt disrespected by any of my posts than I apologize for that. Due to your lack of knowledge about me I will also brush off the insult to my intelligence as I have nothing to prove to you. My work in the business world speaks for itself...it saves lives.



You sir are a gentleman and a scholar. Very good info...thanks for posting.

You just ain't hit the right button for Been to set you straight.

He gets gets compliments all day which are well deserved.

You just happen to it my button and you got what you deserved.

Where i live had I made a house call to your residence and found you blotto and messing with a gas appliance I would have had you arrested
for reckless endangerment to life and property.
 
#45 ·
The pressure switch is a safety device.

Buy passing it, doesn't mean its the problem.

It may have been doing its job.

If you install a new switch and it doesn't work. Your right back at step step 2.
 
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