Nothing like waking up to 40 degree temps in your own house (20 outside, and -1 predicted for this weekend). Went to check the thermostat and it was dead (or at least appeared to be). No display nor any response from the buttons. Popped it off and it was missing the batteries (which its never needed before, as its powered from the furnace). I inserted some and the display was restored, but no matter what I did the furnace did not ignite.
Checked and reset the breakers, the gas stove, fireplace, and the hot water heater just to make sure everything tied to gas was still functioning properly.
Now down to the furnace which is in the basement, removed the panels, checked the filter, the status led was green and blinking properly, the only oddity was about 2" of water below the furnace in the drip pan.
There is a pump in the pan that should be pumping this water out but its apparently not...if yours is in the attic or a closet you shouldn't have this drain problem as there will simply be a down grade of your drain to get rid of the water automatically. The rust build up had been unseen by me during my many trips in this area because its in the rear of the furnace.
After some fiddling around, checking the transformer and conductivity from the thermostat (if you check the 'C' and 'R' contacts they should register 24v) with a multimeter, and verified that the furnace was still operating.
Down near the pump was a small piece of equipment attached to the side of the pan, it said AquaGuard. OK...thats a good lead. a little more fiddling and googling, and this is apparently the safety cut off switch for the furnace. When the water gets too high in the pan, it actually disables the furnace to keep it from producing more water and flooding your basement. So now panic mode was subsiding, as this was definitely the culprit. I pulled it off of the pan and the furnace cranked right up.
The only problem now is that the pump is supposed to get rid of the water BEFORE the monitor needs to disable the furnace. There is no switch on the pump to start it, it is engaged with a water float, like the type you find in your toilet tank and when the float piece hits a certain angle from being raised by water in its tank, it should start the condensate pump and everyone should be happy.
So, I emptied the drip pan with a wet/dry vac, replaced the pump, and sprayed the pan with a rubber sealant.. Happily I saved $500, not needing a service call and of course Im outside of the warranty period. Luckily a replacement pump runs anywhere from $40-$80 and is a simple install.
While I waited for the replacement pump, it looks like it takes about 2-3 days for the drip pan to refill with water, so thats the only buffer of time you have to get this taken care of before you need to wet vac it again.
A common maintenance step for your high efficiency furnace (which you should have been instructed to do by your PM or HVAC installer) is to dump approximately a liter of a bleach/water mix into an inlet tube that feeds the pump every 6 months or making a service change (changing cold to heat or vice versa), it should be capped like this...that feeds directly into your pump to keep it from getting clogged with algae and dirt particles.