Honeywell T9 power interruptions with Taco ZVC404

fiveightandten

I just installed some Honeywell T9 smart stats to my HW boiler system and one of them is hiccuping. Every few hours, the clock will reset, so I'm assuming it's seeing power interruption. I'm hoping for some suggestions as to how to get things running reliably.

SYSTEM SUMMARY:
-Burnham HW boiler
-Taco ZVC404 controller powered by a 40va Tx
-4 Taco zone valves (3 floors + water heater) @ 0.9A each
-Added a second 40va to run the new stats, but Zone 2 is 3 wire cable, leaving me without enough connections to run it off this new Tx.
-Honeywell T9s are said to draw 3va. I'm not running Wifi, remote sensors only.

Thermostats:
-Z1 Basement - 4 wire cable, I haven't swapped out the old 2 wire stat yet.
-Z3 First Floor - 4 wire cable, Honeywell T9 is running fine, powered by a dedicated 40va Tx.
-Z2 Second Floor - 3 wire cable, Honeywell T9 is hiccuping at this location, powered off the 40va Tx that's running the controller / valves.

Questions:
-Is my 40va Tx being overworked? I'm assuming the controller wouldn't actuate 4 valves at once, but 2 of them will technically over run the Tx.
-Is there a way to run Z2 off the new dedicated Tx, given the 3 wire cable?
-If I can't get Z2 on the new Tx, will upgrading the original Tx to a 75va or 100va solve my problem (assuming it even is power starvation)?

STEVEusaPA

Your transformers may be out of phase. To what is the aqua blue line wire running to t-stats 1 & 2 connected?

fiveightandten

STEVEusaPA said:

Your transformers may be out of phase. To what is the aqua blue line wire running to t-stats 1 & 2 connected?

Hey Steve, the blue line is running from C on stats 1 and 3 (not 2) directly to the "C" secondary terminal on the new Tx (dedicated for stats only).

The original Tx powering the board and Zone 2 stat has 2 yellow secondary leads with no labels on them.

Zone 1 (Basement):
This is not hooked up yet (still running 2 wire stat)

Zone 2 (2nd Floor):
R switch set to 1 wire position
W to W on controller
R to R on controller
C to right side "power in" terminal on controller (unlabelled Tx secondary, opposite "R" on the controller)

Zone 3 (1st Floor):
R switch set to 2 wire position
W to W on controller
Rc to new Tx "R" secondary terminal
C to new Tx "C" secondary terminal

HVACNUT

You're butting transformers. You need to install isolation relays for each zone.
Use the separate transformer to power the thermostats R and C.
W off the thermostat to the relay coil.
Common from the separate transformer to the other side of the relay coil.
The Normally Open contacts on the relay to R and W on the zone panel. 
Half my life is spent correcting these issues.

fiveightandten

HVACNUT said:

You're butting transformers. You need to install isolation relays for each zone.
Use the separate transformer to power the thermostats R and C.
W off the thermostat to the relay coil.
Common from the separate transformer to the other side of the relay coil.
The Normally Open contacts on the relay to R and W on the zone panel. 
Half my life is spent correcting these issues.

Thanks for the info. Before I dive into that level of complexity, is there a reason I couldn't just run everything off a single 75va or 100va Tx and ditch the dedicated transformer? It would be adding the one T9 stat (3va), as I don’t really need another for the basement.

fiveightandten

So, as a follow up to this. I moved everything on one transformer and was still having power interruptions. I caught it happening and it looks like it was concurrent with the Zone 4 (water heater) priority switching on the controller.

I turned off Zone 4 priority and the problem seems to have gone away. Any issues with this that I'm overlooking? I upgraded the transformer to a 75VA.

HVACNUT

The issue is with zone 2 only?
If R on the zone panel is connected to R on the thermostat, and C to C, then power to the thermostat shouldn't be interrupted with a domestic priority call.