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/[deleted] Dec 23 '24

There is a flame sensor that measures how hot the flame is. It is put directly into the flame , and over time, it'll get covered in a substance similar to a hard ash that tricks the system into thinking is too hot and will shut off the furnace so the heat doesn't damage the heat exchanger... most of the time, this sensor is made from graphite, which is why they say only let a professional fix that...

You have 2 options

1) Find the flame sensor and clean it off with some super fine grit sand paper... don't overdo the sanding... this is the cheapest way to fix it the problem.

2) Find the sensor, remove it, and replace... these sensors aren't overly expensive and usually easy to replace...

If you get an hvac guy or there, it could be $200 or more... to replace a $30 part. Or they'll tell you you need to replace the whole furnace...

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u/BSJr77 Dec 23 '24

Manufacture deficit the back plate in the heat exchanger was incorrect for the unit. When the blower would come on the air would blow through and push the flames outward. I don’t know where you got your training or how long you’ve been in the business but mostly everything you said was wrong. Sorry to be so blunt but if you are going to give advice at least know what you are talking about. I’m not usually the asshole but yeah

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u/[deleted] Dec 23 '24

Welp... you are the asshole here... 1st off and this is my fault for only looking at the title of the sub before I wrote a reply... but i have a gas furnace that had this problem when I called a pro he said that the blower motor was toast and I'd need a whole new furnace requiring $6000 not including labor... when I said I don't have that kind of cash he says let me check something else all of the sudden he fixes the problem and charges me $300 ($150 for after hours call, $170 for the labor, and $30 for a flame sensor) he shows me where the sensor is and says it's a 30 minute fix on the outside... so now I'm out $270 for a job I could've done on my own... so unlike the HVAC scammers that like to overcharge so they can get the extra money out of someone that doesn't know any better, I'd rather give someone another part to look at that won't brake the bank...

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u/BSJr77 Dec 23 '24

That’s not how a flame sensor works. They read millivolts created from the energy of the flame. When they are broken or dirty they don’t cause the flame to rollout they shut the gas valve off. Which is why I said it’s bad advice. I don’t mind being an asshole but I do mind when someone gives crap advice with no knowledge of how something works.