I get three red flashes from the furnace after an attempt sequence when the t-stat calls for heat. The motor starts, and seems to try to light but after about thirty seconds, it quits and gives the error code.

I have removed both gray tubes from the pressure switch and made sure they are clear of obstructions. I have blown/sucked slightly on them to hear the 'click' from the pressure switch.

I have 'jumped' (?) the pressure switch with a paperclip (having removed both wires and using the exposed contacts) and it won't fire up then either.

I have also removed the burner cover and tried to start it but while it didn't work initially, it did start later (the only time it's worked since initially giving the error) with the cover off, but this could've been due to messing with the wires on the pressure switch?

Does the "jump" experiment indicate a BAD pressure switch and a new one would solve my problem? This is only a 3 year old furnace!

Please help!

The "jumper" test must be performed in a way that matches the operating sequence of the unit; that is, you cannot jumper the wires together until after the inducer starts. If you jumper them before the inducer starts, the unit will assume the pressure switch was stuck closed all along and "fault out".

I did this and it still didn't kick on.
UPDATE: After randomly disconnecting and reconnecting both wires to pressure switch, furnace will end up starting. This must indicate a faulty pressure switch if it's so temperamental, right?

Not a sure thing, but definitely the leading candidate.

I occasionally get 5 flash fault codes. I find that turning the furnace off then back on again (on the unit itself) fixes the problem for now, until I can get my HVAC guys to come look at it.
If you have misplaced, the manual, here are the fault codes with possible problems/solutions below:

SLOW GREEN FLASH: Normal operation.
SLOW AMBER FLASH: Normal operation with call for heat.
RAPID RED FLASH: Twinning error, incorrect 24V phasing. Check
Twinning wiring.
RAPID AMBER FLASH: Flame sense current is below 1.5 microamps.
Check and clean flame sensor. Check for proper gas flow. Verify that
Current is greater than 1.5 microamps at flame current test pad.
4 AMBER FLASHES: The control is receiving a “Y” signal from the
Thermostat without a “G” signal, indicating improper thermostat wiring.
1 RED FLASH: This indicates that flame was sensed when there was
Not a call for heat. The control will turn on both the inducer motor and
Supply air blower. A gas valve that leaks or is slow closing would typically
Cause this fault.
2 RED FLASHES: This indicates that the normally open pressure
Switch contacts are stuck in the closed position. The control confirms
These contacts are open at the beginning of each heat cycle. This would
Indicate a faulty pressure switch or miswiring.
3 RED FLASHES: This indicates the normally open pressure switch
Contact did not close after the inducer was energized. This could be
Caused by a number of problems: faulty inducer, blocked vent pipe, broken
Pressure switch hose or faulty pressure switch.
4 RED FLASHES: This indicates that the main limit switch has opened
Its normally closed contacts. The control will operate the supply air
Blower and inducer. This condition may be caused by: dirty filter,
Improperly sized duct system, incorrect blower speed setting, incorrect
Firing rate or faulty blower motor. Also, this fault code could be caused
By a blown fuse located on the circuit board.
5 RED FLASHES: This fault is indicated if the normally closed contacts
In the rollout switch opens. The rollout control is manually reset. If it has
Opened, check for proper combustion air, proper inducer operation, and
Primary heat exchanger failure or burner problem. Be sure to reset the
Switch and cycle power (24 VAC) to the control after correcting the failure
Condition. Also, this fault code could be caused by a blown fuse
Located on the circuit board.
6 RED FLASHES: This indicates that after the unit was operating, the
Pressure switch opened 4 times during the call for heat. If the main
Blower is in a “Delay on” mode, it will complete it, and any subsequent
Delay off period. The furnace will lock out for one hour and then restart.
7 RED FLASHES: This fault code indicates that the flame could not be
Established. This no-light condition occurred 3 times (2 retries) during
The call for heat before locking out. Low gas pressure, faulty gas valve,
Dirty or faulty flame sensor, faulty hot surface ignitor or burner problem
May cause this. The furnace will lock out for one hour and then restart.
8 RED FLASHES: This fault is indicated if the flame is lost 5 times (4
Recycles) during the heating cycle. This could be caused by low gas
Pressure, dirty or faulty flame sensor or faulty gas valve. The furnace
Will lock out for one hour and then restart.
9 RED FLASHES: Indicates reversed line voltage polarity or grounding
Problem. Both heating and cooling operations will be affected. Check
Polarity at furnace and branch. Check furnace grounding. Check that
Flame probe is not shorted to chassis.
10 RED FLASHES: Flame sensed with no call for heat. Check gas
Valve and gas valve wiring.
11 RED FLASHES: This indicates that a primary or auxiliary limit switch
Has opened its normally-closed contacts and has remained open for
More than five minutes. This condition is usually caused by a failed
Blower motor or blower wheel. Cycle power (24 VAC) to the control to
Reset the hard lockout condition after correcting the failure condition.
12 RED FLASHES: This code indicates an open igniter circuit, which
Could be a disconnected or loose wire or a cracked or broken igniter.
STEADY ON RED: Control failure. Replace control board.
60-MINUTE AUTOMATIC RESET FROM LOCKOUT: This control
Includes a “watchdog” type circuit that will reset from a lockout condition
After 60 minutes. Operational faults 6,7,8 will be reset. This provides
Protection to an unoccupied structure if a temporary condition exists
Causing a furnace malfunction. An example would be a low incoming
Gas supply pressure preventing unit operation. When the gas pressure
Is restored, at some point the “watchdog” would restart the unit and provide
Heat for the house.

Now I'm getting a six-flash code. Time to get the guys out here to look at it. Luckily, it did restart after one hour, just like it is supposed to.
Oh, and I feel really dumb, but I could not find a window in the bottom panel to view the fault codes. I had no idea the Energy Star sticker was placed over the window and all I had to do was lift the sticker. Ooops.

So, what did the guys say was the problem? Just asking since having furnace problem(stupid code says pressure switch stuck on close, but I went to local parts place and they tested the switch and it is operating properly). The draft inducer won't even start, but if I diconnect(did only for a few seconds) the plug from the circuit board that goes into the pressure switch, the draft inducer kicks in.

Thanks,
Ceci