Exploding Zone Valve windings

MacPHJr

Got a no heat call today from another plumber. He originally got the call from the customer on Friday. It is a steam boiler with two hot water zones. The steam works. The problems is with the hot water zones.



Each zone has a taco zone valve and a relay to control the pump. The first plumber changes the pump, a zone valve head, and the old honeywell relay to a taco sr 501. System works for a couple hours and then it stops. Then I get a call.



The zone valve head looks likes the windings exploded . I tested voltage to the zone valve. 24v from a single transformer.



I blew up another zone valve head just trying to figure out whats going on.



Before it blew up it seemed to work for a few minutes.



I dont know whats going on.

Slimpickins

Might be time

I think it might be time to call in a professional

icesailor

Exploding windings?

None of us know it all.

The only stupid question is the one not asked.

You may have checked the voltage but did you check it when the thermostrat was calling and the boiler and all the controls were working? I think that when the new 501R control was installed, it caused a phasing/voltage problem. I think you may be seeing more than 24 volts. Like maybe 48 volts. If the 5** Taco zone valves are wired the "old" way and have their own 24 volt transformer, the transformer could be bad. If you have a "Amp Mate" that will tell you the amp draw through the thermostat, it should be .9 amps. I usually wire or see them wired with three wire T stat wire with the red, white and green going to 1, 3, and 3 terminals. Take the red top #1 terminal off and connect the AmpChamp. With the thermostat calling, it should read .9 amps. Put the red wire back and try the #2, middle white wire. It should show .9 amps. Try the #3 wire/terminal the same way. The wires to the thermostat should come from the stand alone transformer. #2 and #3 should go to the TT terminals on the 501 relay. There's two sets of TT terminals on that relay because it will replace a Honeywell R832 or an R845. Because that relay will replace any relay made, it is probably wired for the wrong application and you are getting the wrong voltage.

Be EXTREMELY careful when TS'ing the power head. It's a "Wax Motor Valve" and if it overheats, and the full open switch doesn't open, the expanding wax can blow through the side of the cylinder. The only thing containing it is the coil windings around it. If the wax gets on you when it blows, it can cause serious burns.

Also, while you have the head off, take a big pair of water pump pliers and manipilate them so you can squeeze the valve open. It should open easily. It should pop closed easily. Squirt some Kroil on it if you have any. If there is any rust  around the top metal plate where the piston comes through, the piston may be sticking and causing excessive pressure to open the valve, Though, usually, it is the other way around. It sticks open.

The problem started when the relay was changed to a 502R? Look there.

Tim McElwain

It could be possible that

you have two secondaries of transformers wired in series giving 48 volts to the heads.The best thing to do is separate the transformers.  That is not a phasing problem, phasing problems with transformers do not damage zone valves they burn out transformers.



Wiring as follows:



Off the "R" terminal on the transformer to the thermostat, out of the thermostat to terminal 1 on the zone valve. Terminal 2 on the ZV goes back to the other side "C" on the transformer. Then wire from 2 to T on the relay and 3 to the other T on the relay.



TACO zone valves rarely draw .9 they are usually around 1 amp to 1.1 so set the anticipator on the thermostat to 1.2, it will work a lot better.



When you think you have it wired correctly instead of powering the head and losing another one connect your multimeter on the # 1 wire and #2 wire on the zone valve and see what you get for voltage. Should be around 24 volts if not then something is wired incorrectly.

icesailor

Phasing:

Sorry, I used the wrong term, "phasing". Same thing though. If the system worked until the 501R was installed, I would be looking for a wiring issue.

I'm not an electrician and only self taught from needing to resolve problems "others" couldn't. Terminals #1 and #2 have another transformer load. #2 and #3 have a transformer load. Where and how they meet is where the problems may arise. They meet at Terminal #2.

I've never seen a Taco 5** zone valve head do that in 40 years of using them. If the motor can't "push" the plunger down, and can't switch the power off, maybe it could do this. But you didn't say that the valve didn't work after changing the head. So, something else is causing it.

Loose connections can cause things like this.

Joe Mattiello

zonevalves proper wiring



Operation of the 571 Taco, zonevalve.

 

The motor (actuator) of the 571 is a heat motor. There is an electric heater wrapped around a wax filled chamber, and a thermostat calls for heat, 24 volts is applied to the 22 ohm heater.

 

When the valve has opened .125 to .150 thousands of an inch " the heater is turned off.  However, if any system debris hinders the piston from extending the full throw, the heater stays engaged ultimately resulting in a failed actuator.  After working on the system it’s entirely possible something became lodged in the valve cavity.  Another consideration is iron oxide buildup, which can limit the pistons full range of motion. 

 

Taco offers the replacement actuator, and valve seat assemblies in addition to the entire valve.  (See replacement parts list attached).  I also included a technical bulletin with a comprehensive explanation of the valves functionality.   

 

Hopefully, this information helps.  If you have any questions or concerns I encourage you to call Taco tech support where we have technicians ready to assist you.   

Joe Mattiello

zonevalves proper wiring