I checked all the breakers and they are not tripped.
The unit has a switch with a pilot light and it is on.
I did try to turn the switch off. When I did that a barely noticeable
hum stopped. I turned the switch back on and the hum is back.
I took a voltage tester and got 10V -5V 9V 1V. I don't see too well
and the lighting at the thermostat is low, but I assumed the terminal
that was the last wire on the block was the common.

What next? Buy another thermostat?

On Wed, 21 Feb 2018 18:15:37 -0500, Seymore4Head
wrote:

I checked all the breakers and they are not tripped.
The unit has a switch with a pilot light and it is on.
I did try to turn the switch off. When I did that a barely noticeable
hum stopped. I turned the switch back on and the hum is back.
I took a voltage tester and got 10V -5V 9V 1V. I don't see too well
and the lighting at the thermostat is low, but I assumed the terminal
that was the last wire on the block was the common.
What next? Buy another thermostat?


I had to replace mine this year - after discovering the batteries
were badly corroded - my neglect - forgot that it had batteries ..
John T.

On Wed, 21 Feb 2018 18:37:06 -0500, wrote:

On Wed, 21 Feb 2018 18:15:37 -0500, Seymore4Head
wrote:

I checked all the breakers and they are not tripped.
The unit has a switch with a pilot light and it is on.
I did try to turn the switch off. When I did that a barely noticeable
hum stopped. I turned the switch back on and the hum is back.
I took a voltage tester and got 10V -5V 9V 1V. I don't see too well
and the lighting at the thermostat is low, but I assumed the terminal
that was the last wire on the block was the common.
What next? Buy another thermostat?


I had to replace mine this year - after discovering the batteries
were badly corroded - my neglect - forgot that it had batteries ..
John T.

I was wondering about batteries. Mine swings open to the terminal
compartment. Were the batteries in the same compartment as the
terminals? I hope there are not batteries on the opposite side of the
printed circuit board. I haven't tried to take that apart yet.

On 2/21/2018 7:12 PM, Seymore4Head wrote:
On Wed, 21 Feb 2018 18:37:06 -0500, wrote:

On Wed, 21 Feb 2018 18:15:37 -0500, Seymore4Head
wrote:

I checked all the breakers and they are not tripped.
The unit has a switch with a pilot light and it is on.
I did try to turn the switch off. When I did that a barely noticeable
hum stopped. I turned the switch back on and the hum is back.
I took a voltage tester and got 10V -5V 9V 1V. I don't see too well
and the lighting at the thermostat is low, but I assumed the terminal
that was the last wire on the block was the common.
What next? Buy another thermostat?


I had to replace mine this year - after discovering the batteries
were badly corroded - my neglect - forgot that it had batteries ..
John T.

I was wondering about batteries. Mine swings open to the terminal
compartment. Were the batteries in the same compartment as the
terminals? I hope there are not batteries on the opposite side of the
printed circuit board. I haven't tried to take that apart yet.


I've had this problem and part of mine swings open with just the
batteries. Maybe google up your model and see how it works.

On Wed, 21 Feb 2018 18:15:37 -0500, Seymore4Head
wrote:

I checked all the breakers and they are not tripped.
The unit has a switch with a pilot light and it is on.
I did try to turn the switch off. When I did that a barely noticeable
hum stopped. I turned the switch back on and the hum is back.
I took a voltage tester and got 10V -5V 9V 1V. I don't see too well
and the lighting at the thermostat is low, but I assumed the terminal
that was the last wire on the block was the common.

What next? Buy another thermostat?

I got a copy of the user manual and it looks like all the thermostats
operate at 24V. The drawings all say that the common terminal is
labeled C and the hot is labeled R.

I took a tester and I get almost 12V.

On Thursday, February 22, 2018 at 3:59:53 PM UTC-5, Seymore4Head wrote:
On Wed, 21 Feb 2018 18:15:37 -0500, Seymore4Head
wrote:

I checked all the breakers and they are not tripped.
The unit has a switch with a pilot light and it is on.
I did try to turn the switch off. When I did that a barely noticeable
hum stopped. I turned the switch back on and the hum is back.
I took a voltage tester and got 10V -5V 9V 1V. I don't see too well
and the lighting at the thermostat is low, but I assumed the terminal
that was the last wire on the block was the common.

What next? Buy another thermostat?

I got a copy of the user manual and it looks like all the thermostats
operate at 24V. The drawings all say that the common terminal is
labeled C and the hot is labeled R.

That's right. Assuming there is a common wire, minimal installation
there is only the R wire.



I took a tester and I get almost 12V.

If you have 12V instead of 24V, you may have a failing transformer or
a partial short. Was that 12V measured as AC and with the thermostat
disconnected? Some thermostats use the 24V to power the thermostat
light, others use the battery. The ones that are powered off the
furnace generally have the backlight on all the time, the battery
powered ones only when you're adjusting it.