[Ferdy]

Furnace under 5 years old and in warranty and with a maintenance contract. Since install over the past few years, there has been an intermittent issue of the blower continuing to run after system reaches temp set by stat. Blower continues to run for 60 - 80 minutes continuously after burner goes out. Technicians have never been able to get here in time to see the blower running before it switches off after 80 minutes. They have run numerous diagnostics and cannot replicate the fault and we get billed for each visit with no elimination of the fault. Issue has worsened over the past 10 days where this has happened 7 times and often in the early morning hours, but not always at this time. Switching off main circuit breaker is the only way to shut it down as the state control will not do this. Circuit board has been replaced as they had no idea what else to do. I have just seen the red light flash code on the board - 2 blinks.
What is the remedy to rectify this as they keep going round in circles?

 

[beenthere]

System lock out. Either the burners are not lighting after 3 tries. Or its tripping on the high limit 3 times in one heat call.

Is the air coming out of the closest register to the furnace real warm/hot when it works.

 

[yuri]

The unit is cycling on the high temp limit control. If the furnace sees an open limit control it thinks the furnace is overheated and will continuos run the fan. They need to do a temp rise check on it to see if it is running too hot. Due to a dirty AC coil, undersized ducts or too many registers closed. Reason it does it in the AM is that it is colder and needs to run longer.

 

[Ferdy]

Air temp

The registers are all open and the heat level of the air from them is warm, it is never what I would consider as being hot.

 

[beenthere]

What air filter are you using.

 

[Ferdy]

Trane XB80

Trane Clean Effects Whole House Air Cleaner

 

[beenthere]

Those are nice filters. You probably have low air flow. Because the contractor probably didn't size your return ducts big enough for the air cleaner.

 

[yuri]

The limit control on some Tranes is 170 deg F and can be as low as 150 deg F. This temp is measured INSIDE the furnace by the heat exchanger. Beenthere is correct. They did not check the temp rise and it has been short cycling on the limit control for 5 yrs. It is now weak and WILL fail soon. I would want the temp rise checked and fan speed increased if possible and more than likely that control is next to shot. Of course they will deny it but that is the problem and needs to be taken care of and will decrease the life of the furnace heat exchanger as well.