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Old 11-02-2010, 10:06 AM   #1
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Tempstar NTC5075BFC1 No fire.


Hey HVAC guys, I could use some help with this old Tempstar 80% furnace. Model #NTC5075BFC1.

On a call for heat, the inducer runs, HSI glows and lights the pilot, and the burner never fires. It sits for probably 15-30 minutes with the pilot lit and inducer running, and eventually gives up for a while.

No diagnostic LED on this model.

Any pointers on where to start? It's an intermittent problem, but getting worse.

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Old 11-02-2010, 05:13 PM   #2
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Tempstar NTC5075BFC1 No fire.


Does it have a gas valve with the numbers SV8500 or close to that?

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Old 11-02-2010, 05:25 PM   #3
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Tempstar NTC5075BFC1 No fire.


That seems familiar. I know it's one of the Honeywell smart valves. I can't remember the exact number on it, but I'll take a look if it acts up again.

We had a tech come out, and naturally couldn't reproduce the problem while he was here. He couldn't really figure out what the problem could possibly be. I let him replace the pilot assembly, thinking that either the flame sensor signal is occasionally too weak, or the gas valve is occasionally not reacting to the flame sensor signal. The pilot assembly seemed like a good starting point, since it's the cheaper of the two parts. Does that seem like a reasonable course of action?

Now I'll just be waiting to see if it happens again.
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Old 11-02-2010, 05:34 PM   #4
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Tempstar NTC5075BFC1 No fire.


Pretty sure it has the infamous dumb valve. Heat exchangers cracking are another common problem with those units. I would invest my $$ in a new high efficiency furnace. That valve is noted for intermittent problems.
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Old 11-02-2010, 05:46 PM   #5
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Tempstar NTC5075BFC1 No fire.


Indeed. I've heard of the problems with these valves. The tech did indicate that the heat exchanger appeared to be fine. He said the valve is not from the first generation which was particularly prone to cracked solder joints on the pilot connector.

Money is tight here, so the plan right now is to see if it runs right with a new pilot assembly, and if it acts up again, use the home equity loan for a new 90% furnace. I figure there's no sense in paying for a new gas valve in this thing.
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Old 11-02-2010, 05:56 PM   #6
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Tempstar NTC5075BFC1 No fire.


Your fed govt apparently has some rebates until Dec or the end of the year for high eff units and I would check your local govt and utility co. No point missing out on them. That valve will get progressively worse and we do service calls on XMAS day and every other day so it may go then. Gets pretty cold in Minnesota and the Dakotas I hear.

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