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I have a York TG9S080B12MP11A up-flow configured natural gas furnace. We have had the furnace since 2007. I am having an issue where the furnace is not starting correctly.

  1. When I power up the blower motor starts up
  2. If I activate the thermostat (I'm using Nest) the indicator light will blink 3 orange pulses.

Now if I turn off the thermostat, unplug one of the cross connectors between the two pressure switches, turn on the thermostat. The fan turns on, and if I reconnect the cross connector the furnace will sit for about 5 seconds with the blower and the fan running. Then the igniters will start to glow and then the gas will kick on.

The furnace will then run until it comes to temperature and then the furnace will shut down but the blower will stay on.

Last year I replaced the switches, the control board. Last week I replaced the condensate pan (original clear model had cracks in it), the blower motor, put in new switches.

Any ideas?

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    Why did you replace the pressure switches? Has it worked properly since you've done the most recent replacements? This sounds like there is an abnormal pressure situation, have you checked the tubing to the pressure switches, your condensate trap, intake and exhaust piping for blockages? – PhilippNagel Dec 19 '18 at 20:36
  • Phillipp I think nailed it. It's also hard for anyone to post the answer to this since we can only guess given the information you provided. But educated guess it is, Philipp is right. The pressure switches are safety mechanisms, you are "bypassing" or tricking the start cycle. Take them off, clean them, check resistances, make sure they are the EXACT same as orig values, and check all plumbing work for them. Its probably physical blockages. – noybman Dec 21 '18 at 21:24
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To the OP, please edit your question and add answers to the questions asked by @PhilippNagel and more answers can be given that are more helpful and less guesswork.

If everything you have replaced is still good, was replaced properly, then you've limited yourself to replacing more parts (shot gunning) which it seems you have been doing all along and wasting money. Ideally what you would do is test the parts, read furnace error codes, and troubleshoot the fault.

You may have a dirty/clogged heat exchanger, since you've mentioned it can be tricked into running until it gets up to temp. I literally just had my Heat Exchanger replaced under warranty today (irony), and my unit was installed in 2010. I just called the installers the previous owner used and they were wonderful. Didn't cost me much and my furnace is working again.

I suggest you do the same unless you have the tools and know how to troubleshoot instead of replacing parts repeatedly.

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