On 4/20/2018 11:13 AM, trader_4 wrote:
On Friday, April 20, 2018 at 12:48:48 PM UTC-4, Bob F wrote:
On 4/19/2018 2:35 PM, wrote:
On Thu, 19 Apr 2018 13:53:48 -0700 (PDT), Robert11
wrote:

Hello,
Have a typical Honeywell Thermostat that controls our home's
gas forced hot water heating system.
Can't find the manual for it, or a model number on it.
Model is probably on the back, and I really don't want to take it off of the wall.
It's a rectangular unit, about 2 years old.
Has a digital display showing the Set Temp., and what it senses as the actual temp.
Runs off of two AAA batteries. Nice green backlighting when the button that sets the Set Temp is pushed.
Would like to have a better understanding of how it works.
a. Question: Do these thermostats, when turning on, merely provide, in effect, a contact
closure for the control box mounted on the furnace ?
And that there is a 24 transformer inside this control box, as well as a relay to control the 110V Circ..
When turning on, therefore, the thermostat just closes its contacts allowing
the voltage from a transformer in this furnace mounted box to then
provide 24 volts to a relay, via the thermostat, also in this control box ?
Is this the way it probably works ?
With only two 1.5V AAA batteries, I cannot see how the thermostat could provide any 24 V.
So, it only closes a set of contacts in its (the thermostat's) case when it is calling for heat ?
b. If the batteries go dead, will the thermostat still function ?
I realize the display won't light up anymore.
Thanks,
Bob


It just pops out of the wall bracket - maybe.

I just had to replace my 8 year old thermostat -
- the touch-screen was failing to adjust certain settings -
including the set-temperarture - it was stuck on 64 F. degrees.
I discovered the 3 AAA batteries had corrosion - no doubt
after being neglected for 8 years ! The other little 3 volt battery
that was well-hidden - seemed fine. I replaced it in an attempt to
reset / revive the unit - to no avail.
I'm not positive that the cause was the batteries but I can't
think of anything else to blame ..

https://yourhome.honeywell.com/en/pr...ostat-rth8500d

John T.



The touch screen contacts may be failing. You could try pushing and
holding the buttons, and see if they start working after a few seconds.
Or take it apart and see if some part between the screen and the switch
it operates is broken.

Say what? The OP said nothing about any problems with it, they only asked
how it worked.

I did not reply to the OP.