Heat Pump doesn't shut off at setpoint temp and aux heat kicks in


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Old 03-20-14, 07:09 AM
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Heat Pump doesn't shut off at setpoint temp and aux heat kicks in

We just recently purchased our first new home and it came equipped with a trane HP and a trane Taystat 540 programmable heat pump thermostat. I have never had a heat pump before so I apologize if I seem ignorant. Currently, I have the temp set at 65 at night and while we are away at work for the day and 68 while we are home and awake. I understand that the aux heat comes on in the mornings to help it get from 65 to 68 quickly. However I wish it would not come on at all and just allow the heat pump to get that house up to setpoint. This morning, the outside temp was only in the low 40s and the aux heat kicked it twice to help the temp reach 68. Well once it did reach 68, the heat pump never cut off and the aux heat continued to come on WHILE the display read 68. As I left for work this morning, it still had not cut off. What can I do to keep aux heat from cutting on at all, and why don't the heat pump cut off once it has reached setpoint and has been at setpoint for 10+ minutes?
 
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Old 03-20-14, 05:42 PM
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Welcome to the forums.

I was looking at the manual for that thermostat and it doesn't say anything about changeover temperature. I believe the electric reheats come on if the temperature increase is three or more degrees. Perhaps a change of thermostats is in order.

A link to your thermostat manual.PDF


The forum pros will stop by and offer their opinions too.
 
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Old 03-21-14, 07:40 AM
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Thanks for the reply. I believe I will keep the thermostat at 65 with no setback. It is not a thermostat that utilizes "adaptive recovery" and will turn on the aux heat for assistance when the room temp and the set temp are only 1 degree apart for a prolonged period of time, according to the trace customer service rep I spoke with.
 
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Old 03-21-14, 08:08 AM
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THe issue may come down to the interpretation of set-point being reached. for example, my thermostat considers set point reached when the temperature just exceeds that temperature, e.g
set point at 68, temperature differential 1 degrees. Call for heat when temperature falls to 67.99999, heat on through 67 (an instant), through 68, off when 69 just reached.
In other words cycle on at 67.99999 , off at 68.9999999;
I think you are expecting on at 67.0000000001 off at 68.0000000000001

I guess different manufacturers have different philosophies about what set point 68 means - is it 68.0001, 68.5, 68.9999999999 it's easy to make an argument for any of these variations being correct ... and for that matter, what a 1 degree differential means precisely...

Assuming your thermostat is ok, then you may have one designed with the 68.99999 philosophy - does the temperature ever indicate 69 for more than a minute when the set point is 68 and the unit cycles off?

As for the AUX coming on when the set-point is more than 3 degrees above room temperature, on my thermostat(and I think most?) this is a parameter that can be changed in the set-up; if so, change it to 5 degrees (say) .
 
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Old 03-22-14, 02:29 PM
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When the outside temp is in the 40s the heat pump should run up to temp and shut off. I would have the HVAC contractor come and check it. Something's wrong.
 
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Old 03-28-14, 09:07 AM
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Thank you so much for your input and to answer your question, no, it the temperature does not indicate higher than the set point for more than a minute. And that makes a lot of since about the parameters as to why the unit continues to run even when the set point is displayed. I think I will call the manufacturer and find out how the thermostats parameters are set up with my particular model. However, they did say that the aux heat will cut on when the heat pump is one degree within the set point and can't seem to reach it after a while. They said there was no way to change this parameter.
 
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Old 03-29-14, 12:31 PM
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It's hard to believe that the temperature differential for activating AUX and/or the "after a while" time are not adjustable - hey, this is supposedly a modern thermostat.
Curious, I went to Trane.com looking for a manual ... and was quickly reminded why I'd never buy anything from Trane: product details unavailable or well hidden.
Searching the internet for " trane Taystat 540 programmable heat pump thermostat" does bring up several sites offering manuals ; maybe worth some surfing, or maybe you'll be able to get manuals from Trane . In the long run you'd certainly like to know how to adjust the thermostat features of(and the rest of the system for that matter) - the very thing manuals usually provide. ... good luck
 
 

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