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So I had some problem with my gas furnace and a technician came by to install a new one but it doesn't have the same rating and only has one tube instead of two. He assures me it's fine but I thought all furnace repairs had to be made with OEM parts? Can anyone let me know if this is safe and if it will affect the life of my furnace?

The furnace is a Lennox ML195 Single stage 95% efficiency furnace. He replaced the whole pressure switch but the new one has only one port whereas the old one has two, so now there is a hose that is unconnected on one end. Also the old pressure switch has a rating of 0.90 PF and the new one says 0.27" WC is that the same?

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    Hello, and welcome to Stack Exchange. My guess is that the exchange will be fine, but we'll need a lot more information to be sure, e.g. the make and model of the furnace, and exactly what was replaced (the whole thing?). – Daniel Griscom Feb 13 '18 at 2:34
  • It's common practice for HVAC technicians to use non-OEM parts. As long as the pressure switch has the same rating, it should be fine. – Tester101 Feb 13 '18 at 3:02
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The documentation for your furnace, calls for a switch rated at 0.90" wc. Using a switch with a lower rating, means that the switch may be closing without the proper inducer air flow.

If you called the tech out because the furnace was not working, you may have a problem that was preventing the switch from closing. By putting in a different switch, the tech might just be ignoring a big problem.

There are three main reasons that a combustion air pressure switch would not close.

  1. Obstruction/restriction of the air intake.
  2. Obstruction/restriction of exhaust.
  3. Backed up condensate.

Pressure switches can go bad. However, they are more often than not an indicator of a problem, not the problem itself.

I'd call the company, tell them your concern, and ask them to send out a different tech to fix the problem.

It's possible that this is a legit remedy, since you say the new switch is only connected to a single port on the unit. This means that, instead of reading the pressure differential across the inducer. The new switch is reading the difference between the pressure inside the unit, and atmospheric pressure. I was not able to find any documentation on this type of substitution from Lennox, so I'm not sure if it's an approved fix or not.

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    This answer is exactly right. That differential pressure switch is the combustion air proving switch, and has two tubes because it compares the exhaust and condensate trap air pressures. If your condensate trap starts leaking, the furnace will still operate if that tube isn't connected and that isn't a fail safe situation. – Dotes Feb 13 '18 at 17:26
  • The company is a one man operation and the guy keeps saying it's fine.. I don't know what to do here guys, I think the guy just scammed for me a quick fix. He came in and with barely any diagnosis says I needed a new pressure switch, and he had one in his car ready without knowing beforehand what furnace I had so I'm thinking he just used one he had laying around. Should I get another technician to install the original pressure switch back? and what can potentially happen if I keep this pressures switch? – wjcmogui Feb 14 '18 at 8:21
  • @wjcmogui Contact a reputable HVAC company in your area, and have them come take a look. Like I said, technicians often use generic parts, because they have limited space in their trucks. However, replacing a part with a generic, is much different than replacing it with the wrong part. It sounds like you got the wrong part, and it should be replaced. If your area has the BBB (Better Business Bureau), you might consider filing a report against the previous technician. – Tester101 Feb 14 '18 at 12:36
  • Is there anything else I can do besides file a BBB report to possibly get a refund? I've already spent over 300 and can't afford to spend more money on this, calling a certified lennox technician would cost me $120 just for a diagnosis, i'm completely bummed out that I let this technician me into thinking it was an acceptable fix, he even showed me all his training certificates and such. Are you certain that its the wrong part and needs to replaced? If so I might just buy the OEM pressure switch and DIY. – wjcmogui Feb 21 '18 at 14:25
  • @wjcmogui Like I said, I couldn't find any documentation from Lennox that stated this was a fix. Probably not much you can do, short of contacting a lawyer. You could always contact the technician that did the work, and ask him to make it right. – Tester101 Feb 21 '18 at 22:11
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Under proper conditions the burner flames could roll out causing a fire and damage to your furnace should the flue become partially clogged. Engineers spent a lot of time and testing to determine the proper switch for the furnace. It is fine to use after market parts but they must have the same rating and design characteristics.

  • The technician put his company sticker on my furnace and he says that is to protect me but i'm skeptical, is that good enough to hold him liable if anything happens? Didn't get a receipt from him – wjcmogui Feb 21 '18 at 14:31

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