I had a York TM9X Furnace installed by a friend (this is what he does for a living) back in November of 2011. It ran great until last December when it started intermittently not starting & Flashing 3 Red Codes (2 or 3 times it flashed 6)
When it does this, I turn it off at the Thermostat and try and restart it several hours later. Eventually it always restarts and it runs for 5 - 14 days without a problem and then it start doing the same thing again.
My friend (the installer) has over and cleaned the flame sensor, cleaned the internal hose, even slopped the exhaust pipe more towards the outside. He suspected it was a condensation problem but he's at a loss at what could be effecting the Furnace.
I'm not looking for DIY instructions, just some ideas that I could pass along to him.
Thank you for your time and suggestions.