Emergency heat stops working

I have a heat pump with resistance backup heat and a Honeywell TH5220D 2H/1C thermostat. The same resistance heater serves as the auxiliary heat to supplement the heat pump or by itself as emergency heat (a setting on the thermostat).

Recently, I found out that if I set it to emergency hear on my thermostat, I do not get any heat, only the fan blowing the air. But the auxiliary heat still works as I can see the display from the thermostat as well as felling the heat from the vent (since auxiliary heat delivers much warmer air than the heat pump). This behavior was verified with the built-in system test.

I have not changed anything recently, and I know emergency heat was working before. So there is nothing wrong with the wiring. I also made sure that the wire that marked for emergency heat in the thermostat still firmly connected in its place and is not broken or anything.

Where should I start to check to see what went wrong?

 

Please tell us the make/model of your heat pump.

 

The electric heat will come on anytime the room temperature is three or more degrees below the set point temperature.

If you stat has an emergency heat position.... then there would most likely be a jumper on the back of the stat from W or AUX to E.

 

I have a Trane XL 1200 with TWV064 air handler and TWX042 outdoor unit, with BAY96X1514 backup heat package.

 

Pjmax,

Yes, it does switch to aux heat when the temp is differ more.

I cannot find jumper between Aux and E, not on the back either. The only jumper is between Rc and R. But this is the same wiring I had with this thermostat (3-4 yrs?), and it worked before.

My installation guide says, "install field jumper between Aux and E if no emergency heat relay." So I guess I must have emergency heat relay. Could it be that's where went wrong? But where is this replay?

 

One more question, what temperature should the air comes out of emergency heat be?