Taco hydronic heating thermostat not working

Lowmiler

Our home has a Taco controlled hydronic system that covers the bathing/kitchen water, the heating of the home, and a bathroom radiant floor.

Suddenly the bathroom radiant floor thermostat, a Honeywell low voltage type, has stopped working. No display. All other water heating in the house is working fine.

The Honeywell thermostat has a red and white supply wire, connected to R and W, and I get 30V AC when bridging those wires. I get the same 30V at the other end of those wires at the Taco controller. To me, that suggested a bad Honeywell thermostat. I installed a new one, and that, too, won't power up.

Kind of lost on next steps in troubleshooting. Any guidance appreciated.

Todd

Alan (California Radiant) Forbes

With only two wires, your thermostats needs batteries. The 30 volts that you're reading is from only one leg of the transformer and won't power the thermostat.

SteveSan

What is the part# of the Taco control? SR or ZVC? Is the green LED power light on? If you jump the R-W to one of the zones, does this turn your system on? Please give us a call 401-942-8000 and ask for Tech Support. We are here from 8am-5pm EST Mon-Fri.

Lowmiler

Alan (California Radiant) Forbes said:

With only two wires, your thermostats needs batteries. The 30 volts that you're reading is from only one leg of the transformer and won't power the thermostat.

Well, I guess the first set of batteries I put in were “brand new duds”, because I got home and tried another set and bingo, we’re back online.

Thanks for the help!

STEVEusaPA

Lowmiler said:

Well, I guess the first set of batteries I put in were “brand new duds”, because I got home and tried another set and bingo, we’re back online.

Thanks for the help!

That actually happens often. Customer replaces batteries and it doesn’t work. I put in my batteries, it works.
Another common issue is not locking it back on the base properly, and/or bending a pin.