First let me give you some history. We have an American Standard 90 two stage propane furnace that is just 4 yrs old. We have been fighting this issue for two years and it has gotten worse this year. We have had the dealer we bought the furnace from out to address the issue multiple times and still nothing resolved. The dealer has
1. Replaced the mother board
2. Checked fuel pressure
3. Cleaned thermo coupler
4. We changed filter monthly (give or take a week or two)
5. Checked the intake plumbing for blockage
6. Checked the exhaust plumbing for blockage
7. changed intake pipe to a 90 on top of furnace and disconnected the external plumbing
8. Changed the heat exchanger
9. tried three different thermostats
10. verified wiring from furnace to thermostat was good
11. Verified amperage to furnace from breaker panel was correct
Here is what is going on….and it is not ALL the time.
The furnace will blow cold air. We notice this about everyday and when it starts we notice that the thermostat is about 1 degree below the set temp. The error code on the furnace is 21 green flashes and 1 red flash repeating. We have also gotten error 2 green 1 red/green and red then green.
We have reset and saw the furnace start up. It will call for the flame then fire up then run 2 – 10 seconds then flame out .Its almost like it thinks it has a live flame and initiates the blower and then blows cold air until we shut unit down or blower times out (assume it times out when were not home) . We have had it blow cold for over 20 minutes.
Our furnace guy has been great but he like us is frustrated because we can not get it fixed. I am told it is still under warranty but that’s only for parts and a different furnace is out of the question. I am at my wits end as to what to do here. The next closest dealer is over 40 miles away so I really have no other warranty options to use. If anyone has any ideas I may present to the dealer please let us know.

The thermostat fan is set on auto and heat only. It is wired with red – white - green

First let me give you some history. We have an American Standard 90 two stage propane furnace that is just 4 yrs old. We have been fighting this issue for two years and it has gotten worse this year. We have had the dealer we bought the furnace from out to address the issue multiple times and still nothing resolved. The dealer has
1. Replaced the mother board
2. Checked fuel pressure
3. Cleaned thermo coupler
4. We changed filter monthly (give or take a week or two)
5. Checked the intake plumbing for blockage
6. Checked the exhaust plumbing for blockage
7. changed intake pipe to a 90 on top of furnace and disconnected the external plumbing
8. Changed the heat exchanger
9. tried three different thermostats
10. verified wiring from furnace to thermostat was good
11. Verified amperage to furnace from breaker panel was correct
Here is what is going on….and it is not ALL the time.
The furnace will blow cold air. We notice this about everyday and when it starts we notice that the thermostat is about 1 degree below the set temp. The error code on the furnace is 21 green flashes and 1 red flash repeating. We have also gotten error 2 green 1 red/green and red then green.
We have reset and saw the furnace start up. It will call for the flame then fire up then run 2 – 10 seconds then flame out .Its almost like it thinks it has a live flame and initiates the blower and then blows cold air until we shut unit down or blower times out (assume it times out when were not home) . we have had it blow cold for over 20 minutes.
Our furnace guy has been great but he like us is frustrated because we can not get it fixed. I am told it is still under warranty but that’s only for parts and a different furnace is out of the question. I am at my wits end as to what to do here. The next closest dealer is over 40 miles away so I really have no other warranty options to use. If anyone has any ideas I may present to the dealer please let us know.

The thermostat fan is set on auto and heat only. It is wired with red – white - green

After all of this I believe a call to the manufacturer is in order. It is possible this has happened to other units besides yours. One possibility that from time to time is overlooked by many is the grounding of the unit both internal ground wiring and from the furnace back to the electric panel. The electronics on the newer units is very sensitive especially on grounding. NOW I am not talking about the neutral (usually white wire) but the green or bare copper wire. What most do not realise is the fact that the white neutral and the black are both current carrying wires. The green wire is for ground only and as mentioned before the circuit board based equipment needs a good ground to make sure all harmonics etc are done with so as not to cause circuit board control problems.

Harmonics (electrical power) - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Harmonics_%28electrical_power%29)