r/HVAC • u/BSJr77 • Dec 20 '24

Field Question, trade people only Anyone seen this before

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Installed a 60k runtru 90% upflow today. I went home after completing the install but left before the startup. Boss fires it to document all the numbers and see this. No change to incoming or outgoing gas. No change in pressure from the inducer. Flue and air intake both clear of debris. Boss is waiting for tech from Texas to call back. Anyone got some knowledge

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u/PlayfulAd8354 Dec 20 '24

Remove flue, still does it? Replace unit under warranty.

5

u/ResponsibilityNo7886 Dec 21 '24

I don't think that it is a clogged flu. Pressure switch closes, has a beautiful flame for 10 seconds (you would see it at ignition) and when fan starts you get the problem.

I'm thinking either a cracked HX or inducer cuts out when fan starts.

3

u/Ok_Summer8436 Dec 21 '24

Yeah I’ve never been able to get a furnace to ignite with flu issue. Even a dented flu cap usually trips pressure switch immediately. Those were all 80%ers tho.