Thermostat controlling two zones using TACO contorller

[Nanker]

I just plumbed in a third zone on what used to be a two zone system. I live out in the sticks and won't be able to pick up a third thermometer for a week or two. I have everything wired through a 3 zone TACO controller controlling three honeywell zone valves. I want to run two of my zones (operate two zone valves) from one thermostat by wiring the new zone's thermo termination points parellel with one of the other two zones' thermostat wiring. Of course I don't want to risk burning out either the thermostat or controller (not sure which one is powering the zone valve) if the current draw operating two valves simultaneously will be too large of a load. Can anyone advise? Thanks.

 

[WorthFlorida]

Exactly which TACO three zone unit model number. They are two different ways to control the circulator pumps. If the 120vac is wired to the TACO and each circulator 120vac connection is wired to the TACO, the TACO splits the power. If the TACO unit doesn't have this 120v connection, it sends 24vac to the circulator that switches the 120v's.
https://inspectapedia.com/heat/Taco-SR503-4-Switching-Relay-Instructions.pdf.

You can bridge two zones at the TACO unit on the thermostat side. Bridge over the W lead to Zone 3 from Zone 1 or 2. When there is a call for heat all the thermostat does is operate operate a micro relay on the TACO unit that takes very little current. The circulators are controlled by the TACO unit. It switches the 120v to the circulator motors through a relay.

The R lead gets the 24vac from the TACO transformer and it feeds the 24vac to the thermostat. When the thermostat calls for heat, it switches the 24vac to the W lead (white wire) that operates a relay.

 

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[Fitter30]

Parallel two thermostats normally doesn't bother the other thermostat. Taco control are you using dhw priority? Full model number of taco control and brands and model of t stats.