Taco 571 zone valve opens but boiler does not fire

vandelaycorr

I have 4 zones and only one does not trigger the heat. If another zone fires the boiler I do get heat in the troublesome zone. I found some old threads on here so apologies if this is repetitive. A previous discussion stated the end switch was likely bad. I used a voltmeter to test the three terminals and the voltage and continuity were as expected.

Would trying a replacement head be the next step?

Some posts indicated jumping the wires for the end switch but I am not confident in doing that due to a "rat's nest" of connections in the ceiling (the wires are from the 60's but the boiler is 2 years old). The pros I have hired lately have made many mistakes so I thought I would try troubleshooting first. All other zones work as expected. Thanks!

EBEBRATT-Ed

REV3_HeatMotorZoneValves_Catalog_100-3_070620.pdf

The attached brochure explains the wiring and there is a wiring diagram. Taco valves intermingle the 24 volt valve power wiring and the end switch wiring which is different from other valves which makes it confusing to trouble shoot. Even for some professionals

Find the two "End switch wires". One wire should be on valve terminal #2 and the other on #3.

I would shut the power off. Disconnect and mark the wires on terminals #1, #2, #3. You may have more than 1 wire on a terminal.

Then lift the manual opening lever to open the valve. #2 & #3 should be closed (continuity) with the valve open and they should be open when you close the valve.

Keep in mind when you power the valve open under normal operation they take 90 sec to open.

If the end sw seems not to work you need a new actuator.

EBEBRATT-Ed

REV3_HeatMotorZoneValves_Catalog_100-3_070620.pdf

HydronicMike

I would add, when you shut the power off to the boiler, make sure the power is off to the transformer. Many times it’s wired in front of the shut off switch at the boiler, meaning you may have to turn it off at the emergency switch at the top of the steps, or even flip the breaker. You shouldn’t rewire them hot.

109A_5

If the actual zone valve is not fully opening it may not properly activate the End Switch.

Another test, with all other zones disabled (thermostats turned down) and the problematic zone thermostat active you can jumper terminals 2 and 3 (ONLY) on the zone valve to see if the boiler starts.