I purchased a 90% efficient condensating Concord furnace, model number 95G1UH090CP16 in mid-October of this year with a Honeywell programmable thermostat. When it was installed in October, the weather was mild (in the 50s) and the furnace worked great. However, now that it's December and has gotten quite cold in New England, the furnace is on the fritz despite being brand new. The plumber who installed it (and another guy from the same company) has been out to try to fix it, and cannot figure out what's wrong with it - an HVAC repair guy from a different company was out, and cannot figure out what's wrong with it. The plumber called Concord Tech Support, and they couldn't figure out what was wrong with it - but I haven't had heat for 2 weeks despite temps below freezing, and I have a 1 year old son, so I'm getting a little desperate here. Here's what I know:

- There is 18 feet of piping and 4 elbows (5 elbows allowed with up to 19 feet of piping, so we're below that)
- Everything is properly pitched toward the furnace
- The drain piping etc appears to be installed correctly, and drains into a condensate pump that appears to be functioning properly
- There are no clogs/debris in the intake or exhaust pipes. There is no soot/dirt clogging any parts, it's only been in use for a month and a half
- By all appearances, there is nothing wrong with this furnace except for the fact that it doesn't work

The symptoms:
- If the temps outside are mild, the furnace works fine and keeps my house at the set temperature with no issues. If it gets cold, the following happens:
- Fan turns on, burners ignite, everything works properly for anywhere from 30 secs-3 mins. Then everything shuts down, blower turns on. It doesn't get nearly warm enough to get the house up to temp, but everything turns on and appears to be running properly while it's running
- Sometimes a pressure switch error that indicates the pressure switch trips while the inducer is open (3 blinks) gets thrown. Other times, it's just a solid light, indicating no problem at all (even tho there clearly is one)
- There is water getting into the inducer fan. I do not know where it's coming from. According to the Concord tech support guys, it's not possible. He said the only reason for water in the inducer fan is that the furnace is double trapped (it's not - we did have the drain pipe in the hole of the condensate pump, but it has since been moved to make absolutely sure it's not touching the water when it rises)
- The furnace doesn't drain while it's running, but I believe it should... It drains after the burners go out and everything shuts down
- There is no lock out; if I set the thermostat high (in the mid-70s or 80s) the furnace will kick on and off every half hour or so, but it only runs for a little bit before going out. If I turn the temp down on the thermostat until the request for heat turns off and then turn it back up so the request for heat comes back, it turns the furnace on - I do not need to manually turn power on and off to the furnace, the thermostat does its job, but the furnace only runs for a little while each time
- It is not a thermostat issue, as jumping the wires doesn't solve the problem
- The pressure switch appears to be operating properly, as does the sail switch and the rest of the furnace. There's clearly a drainage issue due to the water in the inducer, but everything appears to be installed properly and the condensate pump is working - also, if it wasn't hooked up properly, it wouldn't work fine in warmer weather

I'm not even looking to DIY this, but I'm not sure what to do at this point - 2 plumbers, an HVAC guy, and the Concord tech support dudes are stumped, and I'm frickin freezing. I have a brand new furnace and no heat - the place I bought it from has a guy who's Concord certified, but he's on vacation for another week (of course). Does anyone maybe have ANY insight that I can pass along to the pros as to what could possibly be wrong with this furnace? Thanks in advance.