Honeywell T8411R Not showing LCD Display.

First, yes, I know LCD Display (Redundent I know but sounds right.) The display stopped working. The settings as follows: Fan: Auto Heat/Cool/Off: OFF
No batteries to change in disply. Checked the fused and the breaker was tripped. Reset breaker. Got back in time to the display to see it vamish. Repeated the process, returned even faster only to find no display. Figured I would call the repair man in the morning and figured wth and set the thing to HEAT. A few minutes later the unit turns on and gives me heat. I get warm and turn it off, not sure if it would do so on it's own. Clueless. Can someone tell me if this is somehting I might can fix (I'm pretty inept) or do I need to call my tech and hope he'll get to me before I need to use the AC. Suggestions anyone? Bonnie P
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On 12/20/2015 11:05 PM, noemail wrote:

So, the thermostat was just acting as a "temperature display"?

!! The breaker was tripped while th ethermostat was in the OFF mode? I.e., it was neither calling for heat NOR cooling?

Suggesting the breaker tripped, again -- in short order (seconds?)

Because it tripped again?

So, it *appears* that the unit is performing its intended function; but the *display* isn't working? The breaker is NOT tripping anymore? Has the display returned while it is providing heat??
You can verify this by using a regular thermometer to measure the indoor temperature AT (nearby) the thermostat and noting when the furnace turns on/off. I.e., if it turns on at 68 and turns off at 69 or 70-ish, then repeats this pattern, chances are the thermostat is set for something "around 69F".
[The difference between the temperature at which it turns on and off is termed the amount of "hystersis" in the control loop. It's rarely "0" as that is inefficient. It's also rarely much more than a few degrees -- as that leads to "comfort" issues. So, if it turns on at 68 and hasn't turned off at 78, it's clearly not working properly!]
If this is observed to be the case, then the device is working properly -- though disheartening that you can't OBSERVE its operation. As such, you'll never kow if it suddenly decides to start operating at 58 degrees -- or 88 degrees! :<
[OTOH, you probably won't FREEZE tonight...]

Are you running a heat-pump, by chance?
Sure sounds like you've got a problem in your furnace/ACbrrr, recirculating valve, etc. How old is the HVAC system? Warranty??
Keep a blanket nearby, just in case :<
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noemail wrote:

Do you have heat pump? Sounds like it is not thermostat problem. Breaker tripping maybe caused by something on the logic control board. 24V AC control transformer maybe suspect. THat 'stat is not battery operated.
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noemail posted for all of us...

It probably has a capacitor as a backup for memory purposes. which is now shot.
--
Tekkie

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On 12/22/2015 1:19 PM, Tekkie® wrote:

--------------------------^^^^^^^^^^^^^^^^^^^^^^

And how does that trip the breaker for the furnace/air handler that is powering the device?
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Don Y posted for all of us...

It is shorted internally.
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Tekkie

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On 12/23/2015 1:38 PM, Tekkie® wrote:

A supercap would never be placed directly across the incoming supply. It represents too low of an impedance. Instead, it would appear "behind" a diode and current limiting resistor -- the resistor chosen to slow the inrush current to the capacitor. The "load" on the capacitor would not need to see any such limitation (though, in reality, the load would be much smaller than the charging current).
Short the capacitor and the "line" won't flinch.
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On Wednesday, December 23, 2015 at 4:08:04 PM UTC-5, Don Y wrote:

now

You could short the secondary on the 24V transformer, which is current limited, and the AC breaker for the furnace would not trip.
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