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Kdavid · 03-26-2009, 10:40 AM

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.

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.

Thanks for your time,
Dave

kenmac · 03-26-2009, 11:19 AM

The ignitor glows & lights the pilot... I see you have a smart valve

Try cleaning the pilot orifice if everything else works

Kdavid · 03-26-2009, 11:33 AM

Quote:

Originally Posted by kenmac

The ignitor glows & lights the pilot... I see you have a smart valve

Try cleaning the pilot orifice if everything else works

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.

kenmac · 03-26-2009, 12:03 PM

........ You should check ignitor Or the connections

**beenthere** · 03-26-2009, 12:56 PM

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.

Kdavid · 03-26-2009, 01:19 PM

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?

hvaclover · 03-26-2009, 02:08 PM

The ignitor should not be over ten ohms..

There is 24 present but its hard to get meter probes into it for a good read.

If you hear gas than your valve is getting power.

Change the igniter.

Kdavid · 03-26-2009, 03:18 PM

Quote:

Originally Posted by hvaclover

The ignitor should not be over ten ohms..

There is 24 present but its hard to get meter probes into it for a good read.

If you hear gas than your valve is getting power.

Change the igniter.

Thanks for the reply.

I meant the igniter is not getting 24V it's actually getting 0V. Maybe the valve is not switching the 24V to the igniter?

hvaclover · 03-26-2009, 03:49 PM

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?

Kdavid · 03-26-2009, 04:07 PM

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.

hvaclover · 03-26-2009, 04:15 PM

Quote:

Originally Posted by Kdavid

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.

You have no heat for four Days? And it's fifty degrees.

Get a new vlave and igniter. The resistance it too high for the igniter. It won't last much longer.

hvaclover · 03-26-2009, 04:20 PM

here's a link to help you http://www.fwwebb.com/pdf/htgcat03/2...t_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.

Kdavid · 03-26-2009, 04:41 PM

Thank you for that link...I actually just got off the phone with FW Webb and they have the igniter in stock...will have to get it tomorrow.

Ok so it seems I need a new valve as per the troubleshooting instructions (no voltage at HSI element output). Thanks for the info man.

hvaclover · 03-26-2009, 04:56 PM

Like I said, get 'em both.

Kdavid · 03-26-2009, 06:02 PM

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.