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Discussion Starter #1
I'll preface my question with the fact that I know NOTHING about how this stuff works.

We have two units at house, one for the downstairs and one for the upstairs.

When the upstairs heat kicks on, the outdoor unit turns and everything seems to work fine.

When the downstairs heat turns on, the thermostat's emergency heat light turns on and the display shows "aux heating." Also, the outdoor unit doesn't turn on as it does for the upstairs heat. The downstairs heat has a propane backup. Since the outdoor unit is not turning on, does that mean it's running full-time on the propane backup? SHOULD the outdoor unit be turning on?

I'm just not sure if there's something I need to have fixed or looked at. Don't want to call a repair man just to have them come and tell me it's working fine. From what I can tell online, it doesn't seem like the downstair's unit should be working on emergency heat all the time. And I'm assuming the outdoor unit should be turning on. It's pouring rain right now, but gonna go out in a few and see about a reset button on the outdoor unit that's not turning on.

TIA for considering my dumb questions!
 

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Discussion Starter #3
My thermostat has two heat settings: Heat, and EmHeat which forces the electric heat strips on. Is yours the same?
mine does both heat settings but it’s just on the regular heat setting and the emergency heat is kicking on
 

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Are the outside units both Heat Pumps? Check to make sure the breaker for the down stairs unit is not tripped in your electrical panel.
 

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Do you have two thermostats -- one for upstairs one for downstairs ?

Where are you located ? What has the temperature been lately ?
 

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You seem to have a dual fuel system for the downstairs. Those types of systems lock out the heat pump at a preset outdoor temp, and only use the aux heat, which in your case sounds like propane.

Emergency heat, is a setting on the thermostat that locks out the heat pump no matter what the outdoor temp is. And you have to manually set the thermostat to that setting.
 

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If it’s pouring rain then it must be above freezing. Your heat pump probably isn’t set to lockout at that high of a temperature but if you post your thermostat make and model then we may be able to guide you to find out how it’s programmed.

Confirm the thermostat isn’t locked into Em. Heat setting like Beenthere mentioned. I think you said it was in regular heat but never hurts to double check the simple stuff first.

Did the downstairs unit work the same as the upstairs unit had previously? Or is this how it’s always operated?

Is the upstairs unit propane backup heat also?
 

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Discussion Starter #8
You seem to have a dual fuel system for the downstairs. Those types of systems lock out the heat pump at a preset outdoor temp, and only use the aux heat, which in your case sounds like propane.

Emergency heat, is a setting on the thermostat that locks out the heat pump no matter what the outdoor temp is. And you have to manually set the thermostat to that setting.
If it’s pouring rain then it must be above freezing. Your heat pump probably isn’t set to lockout at that high of a temperature but if you post your thermostat make and model then we may be able to guide you to find out how it’s programmed.

Confirm the thermostat isn’t locked into Em. Heat setting like Beenthere mentioned. I think you said it was in regular heat but never hurts to double check the simple stuff first.

Did the downstairs unit work the same as the upstairs unit had previously? Or is this how it’s always operated?

Is the upstairs unit propane backup heat also?
Thanks for the replies. Yes, the downstairs unit is a dual fuel system. When we purchased the house we were told that the downstairs unit had a propane backup. The indoor portion of that unit down in the basement has a sticker that says it was converted to propane, so I don't know if that means it's actually fully propane or if it is just propane backup.

My thermostat is the Aprilaire 8466. It was not on the emergency heat setting, just regular heat but the red emergency heat light is on and the display shows "aux heating.". From what I can read online, emergency heat usually kicks in at 35 and below, which was about the temperature we were yesterday. It's going to be up in the 40s today, so I will see if the emergency heat setting still kicks in.

The upstairs unit is not propane backup. Straight electric.

The outdoor unit for the downstairs is a Trane XR, model # 4TWR4030D1000AA. The outdoor unit for the upstairs is a Trane XR, model # 4TWR4024D1000AA. Per the Trane website, those are both heat pumps. I read online if you turn the heat on and the outdoor unit turns on, then you likely have a heat pump. So if these are both heat pumps, it doesn't make sense that one is turning on and the other is not.
 

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Discussion Starter #9
It is currently 41 degrees outside and it's still showing emergency heat and aux heating when the heat kicks on.
 

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Discussion Starter #10 (Edited)
Soooo, now it's 43 outside. When the heat kicks on, there is no emergency heat light and no aux heating on the display. And the outdoor unit turns on.

I guess the thermostat is just set to a pretty high temp to have the emergency heat kick in? Is there a way to change that? I've looked up the manual for my thermostat (Aprilaire 8466) and there is nothing about changing the temp at which the emergency heat kicks in.

Should I just get a different thermostat?
 

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Soooo, now it's 43 outside. When the heat kicks on, there is no emergency heat light and no aux heating on the display. And the outdoor unit turns on.

I guess the thermostat is just set to a pretty high temp to have the emergency heat kick in? Is there a way to change that? I've looked up the manual for my thermostat (Aprilaire 8466) and there is nothing about changing the temp at which the emergency heat kicks in.

Should I just get a different thermostat?
Try setting #16

https://www.alpinehomeair.com/related/Aprilaire_8400_Installation_Instructions.pdf
 

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Discussion Starter #12 (Edited)

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Emergency heat. Is only when you turn the thermostat to emergency heat. Other wise it is aux heat. It use to be very common for the thermostat to show a red or yellow light when the aux heat was on.

They may have the lock out temp set high to avoid defrost cycles for the heat pump.
 

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Discussion Starter #14
Emergency heat. Is only when you turn the thermostat to emergency heat. Other wise it is aux heat. It use to be very common for the thermostat to show a red or yellow light when the aux heat was on.

They may have the lock out temp set high to avoid defrost cycles for the heat pump.
Thanks. Would that be the case for a fairly recent thermostat like ours (Aprilaire 8466)?
 

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Not familiar with that model. But if it uses the same terminal for both aux heat, and emergency heat. Then yes the emergency heat indicator will light up when aux heat is on.
 

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Discussion Starter #16
Well, I dropped the low balance point from 35 down to 30 and it seems to not be kicking on the aux heat/emergency heat any longer. It's 32 out and turning on like normal.

So, if the low balance point is what triggers the aux heating to kick in, what does the high balance point do? Our is currently set to 45. With the low balance point at 30, the aux heating will kick in at that point. What happens when the high balance point is reached?

I kind of miss the old analog thermostats!
 

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Well, I dropped the low balance point from 35 down to 30 and it seems to not be kicking on the aux heat/emergency heat any longer. It's 32 out and turning on like normal.

So, if the low balance point is what triggers the aux heating to kick in, what does the high balance point do? Our is currently set to 45. With the low balance point at 30, the aux heating will kick in at that point. What happens when the high balance point is reached?

I kind of miss the old analog thermostats!
High balance point should lock your aux heat out above that temp so it won’t get used.

Your outdoor sensor may be out of calibration if it’s that far off. You can place a thermometer directly beside the sensor to see if they read similar. It could be external influences that are causing the difference so don’t be too quick to make final judgment until placement has been confirmed correct (sunlight, exfiltration, dryer exhaust, etc.)
 

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Aux heat can't run above high lockout temp, heat pump can't run below low lockout temp. Thermostat can switch from heat pump to aux heat when outdoor temp is between high and low, and indoor temp is below set point.

At least on most thermostats that is the way it works.
 
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