Power outage and thermostats

Had a power outage recently…

My Alarm.com thermostats were working flawlessly for about two years since installation.

Then, I was getting a low battery indicator. After removing the “backup” batteries I noticed that the thermostats were no longer powered?

I originally set them up with the common wire to power the thermostats without powers. Worked perfectly with no problems.

Looking for some insight…I’m guessing it has something to do with the power outage in my home.

However, I have no clue…

test the power wire…see if you’re getting a voltage reading–probably 24V.

Hey Alvin,

Just tested power wire with multimeter…getting 24v…so everything is good there.

what is the model of the thermostat(s)?

Model: B36-T10 RB

i have to ask…where you ever able to verify, before the power outages, if the T-stats would power on without the batteries? Reason I ask is to be sure the wires are landing on the correct terminals.

Also, could you supply a pic of the wiring?

Good morning Alvin.

Absolutely. The thermostats were working perfectly without batteries.

I do remember, about two years ago, when the Tech at Alarm.com navigated me through the set up and we had to “tell” the thermostat how to use the common wire for thermostat power. It worked perfectly?

See attached photo of wiring. The green wire leads to the common at the boiler. I don’t have central AC…just heat.

I do remember, about two years ago, when the Tech at Alarm.com navigated me through the set up and we had to “tell” the thermostat how to use the common wire for thermostat power. It worked perfectly?

During setup you would need to learn the thermostat into the alarm panel while it is powered via AC in order for it to act as a Z-wave repeater and operate on full power mode, otherwise it would go into power save mode and not act as a repeater if learned in while running on battery power.

That doesn’t affect whether or not the Tstat will power on, just how the Z-wave radio behaves.

So you have tested the AC power between RH and C? To be sure, set your multimeter to test AC, then test with the leads connected to RH and C wires. Is it 24VAC?

From the description it really sounds like the common wire may be loose or damaged at the boiler end.

Hello Jason.

So, here is what I did:

  1. Tested by RH and C wires to see if there was an voltage. My first test, I got nothing.

  2. I disconnected the common wires from the boiler and reconnected.

  3. Did a retest and bam…I got 25.7v for my first zone. I pulled the batteries from zone 1 thermostat - works well without batteries.

  4. Tested zone 2 - RH and C…no voltage?

You are correct…it appears that something is up with the common wire.

Weird…how can a common wire go bad?

Thanks again J

I did some more testing because my second thermostat doesn’t recognize the common wire.

Here is what I did:

  1. Used new wire - still no power to the 2nd thermostat

  2. Use wires from the 1st thermostat (which uses the common perfectly) - still no power

I’ve tried every possible configuration and it leads me to the actual thermostat?

Does this sort of thing happen to thermostats? It’s been very reliable for the past two years…

Use wires from the 1st thermostat (which uses the common perfectly) - still no power

By no power, do you mean the thermostat did not power on when attached to the wires?

Are you cutting power to the Boiler before making wiring changes? Attaching live wires to the thermostat terminals can cause shorts to occur.

When the 2nd Tstat is wired to the circuit that was previously delivering voltage, did you test to make sure voltage was being delivered at the time? Switching live wires might also throw breakers or blow fuses depending.

I always shut down power because swapping wires around.

I need to figure out a way to absolutely be sure that it’s not the Tstat.

One is working perfectly on the common and the other isn’t.

TSTAT 1 works on C wire 1 but when you swap the TSTAT to TSTAT 2, that one does not work, then its likely that TSTAT 2 is damaged.

It’s driving me crazy TG!

I need to run a few more tests…before I pull out the sledgehammer on either the boiler or the TSTAT :rage: :laughing: