Digital Heat Thermostat: If Batteries Run-Down, What happens ?


R

Robert11

Hello:

Have a gas, forced hot water heating system.
Was about to order a Honeywell thermostat over the web, but had the
following concern which
just dawned on me.

Am interested in their digital model RTH 5100 which is non-programmable.

It says on their ad sheet that it maintains the set-point if there is a
power outage.
O.K., that's great.

But even if there is house power--

These units require a battery or two.

What happens if the battery runs down while you are away ?
I know, use new, fresh, batteries, etc. But-

Will the furnace shut off if battery runs down ?

Or, is the battery only for the display, and the circuitry still works ? If
so, how, as there's no current when
the circuit is calling for no heat thru the 2 wires.

e.g., with no thermostat battery voltage, does the curcuitry default to a
circuit closed condition, which would
keep the furnace active, or... ?

A bit worried about this.

Thanks,
Bob
 
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E

Edwin Pawlowski

Robert11 said:
What happens if the battery runs down while you are away ?
I know, use new, fresh, batteries, etc. But-> A bit worried about this.
Replace the batteries once a year. I've had programmable state for about 20
years and never had a problem from battery failure.
 
T

trader4

Edwin said:
Replace the batteries once a year. I've had programmable state for about 20
years and never had a problem from battery failure.
Some of the digital models have a failsafe mechanical backup that will
kick in at a fixed low temp like 45. You'd have to pull up the specs
to see if this one has it.

For digital thermostats, I like the Honeywell LCD touchscreen. Not
sure of the model, 8600?. Two key features I like are adaptive
recovery, where you just set it for the time you want the new temp to
be reached, eg 70 at 7AM. Based on experience, the thermostat gets
the furnace going at whatever time prior to 7am that it figures out it
needs to. It also has vacation hold mode, where you can set a temp to
be held for X days before it resumes it's regular schedule.
 
K

Ken

Robert11 said:
Hello:

Have a gas, forced hot water heating system.
Was about to order a Honeywell thermostat over the web, but had the
following concern which
just dawned on me.

Am interested in their digital model RTH 5100 which is non-programmable.

It says on their ad sheet that it maintains the set-point if there is a
power outage.
O.K., that's great.

But even if there is house power--

These units require a battery or two.

What happens if the battery runs down while you are away ?
I know, use new, fresh, batteries, etc. But-

Will the furnace shut off if battery runs down ?

Or, is the battery only for the display, and the circuitry still works ? If
so, how, as there's no current when
the circuit is calling for no heat thru the 2 wires.

e.g., with no thermostat battery voltage, does the curcuitry default to a
circuit closed condition, which would
keep the furnace active, or... ?

A bit worried about this.

Thanks,
Bob
As Edwin stated, if you replace the batteries occasionally you will
never have a problem. But I believe the settings (day, time, and temp)
are lost if the battery gets too low. There is however a default
setting I believe the thermostat will revert to, and that is somewhere
around 70 degrees. So even if you lost your settings, it would not heat
or cool the home excessively. Again, I believe that is what most would
do and that is what mine do.
 
H

hallerb

I added a regular thermostat set at 50 degrees, just in case the
electronic one flakes out.

Cheap insurance if you ask me:)
 
J

Joe

I am not sure of your concern but I went and read the manual to this
thermostat and it is entirely digital as it has no manual switch. It does
not say what it defaults to in case of no power battery or otherwise. My
guess would be off but that is just my guess. In any case if you do not
think you can remember to put new batteries in it or may be away from it for
extended periods of time this may not be the thermostat for you.
You may be better of with one like I have. I have a Robertshaw 9520. It
is a digital thermostat that requires no batteries. I has a manual switch
though for Heat, Cool and Off. With mine If the switch is in the Heat
position and the power fails it comes back on with the heat set at 60, if
the switch is in the Cool position it comes back on with the air set at 80,
if the switch is in the off position it simply stays off.

Joe
 
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B

bowgus

I added a regular thermostat set at 50 degrees, just in case the
electronic one flakes out.

Cheap insurance if you ask me:)
Provided that the electronic one does not fail to say ... 110 degrees
:) Many years ago a buddy came home after a weekend away .. to a
temperature of 90 degrees or so (I don't recall the exact temperature).
I use the trusty old manual thermostats. I have a screwnail stop point
at about 64 degrees ... and I turn it down a 1/2 " when I go out and at
night, or a 1/4 " if I'm working around the house ... and to about a
1/8" of the stop point for sitting around. And I have a wall
thermometer beside it for the reference. Those electronic thermostats
are just not flexible enough for me ... or maybe it's the going to get
my frikken glasses every time I need to access anything electronic
these days :).
 
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G

Guest

Ken said:
As Edwin stated, if you replace the batteries occasionally you will never
have a problem. But I believe the settings (day, time, and temp) are lost
if the battery gets too low. There is however a default setting I believe
the thermostat will revert to, and that is somewhere around 70 degrees.
So even if you lost your settings, it would not heat or cool the home
excessively. Again, I believe that is what most would do and that is what
mine do.
That is what my Honeywell did, too,

aem sends...
 

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