Taco 571-2

[jdelena]

I have a crown hot water furnace with two Taco 571-2 zone valves and two Honeywell T-Stats. The system has worked well for the last 8 years.

Today I noticed the upstairs was cold. The T-Stat was calling for heat but the furnace was not running. When the downstairs T-stat calls for heat the furnace comes on.

I disconnected the #1 wire on the upstairs zone valve and switched it to open thinking both floors would heat up when the first floor needed heat.

The furnace started running with the upstairs t-stat off and the downstairs t-stat not calling for heat. I had to disconnect the zone valves and connect one t-stat to the control box.

question #1 how do I figure out if the upstairs zone valve or t-stat is bad

#2 why did the furnace run with the #1 wire disconnected from the second floor zone valve

Thanks

[NJ Trooper]

If you swap the two zone valve powerheads, and the problem follows the powerhead, you know it's not the t'stat...

If the valves are close to each other, you can just swap the wire from the #1 terminal between the valves. If the upstairs thermometer operates the downstairs valve, you know the t'stat is good.

But 99% of the time, it's the powerhead.

The reason the boiler fired up when you removed #1 and switched to manual open is because you removed the wrong wire.

#1 is the wire from the thermostat to the heatmotor that opens the valve.

#2 is the 'common' wire to both the heat motor and the endswitch.

#3 is the endswitch wire that fires up the boiler. If you remove this wire, the boiler will not start when you manually open the valve.