Anyone else having trouble with Taco 555-050RP Zone Valve heads?

Steamhead

Had a customer this afternoon where the end switch on one of these stuck closed, causing terminal 3 to constantly output 24-volts and keep the boiler running. We had a couple new ones in stock- which both had the same problem. These units have always served well so this was quite a shock.

There's nothing wrong with the wiring.

I'll probably head over to R.E.Michel on Monday with my voltmeter to see if the ones they have in stock are showing the same problem.

Anyone else run into this?

Big Ed_4

Normally the end switch goes bad on no contact . It breaks up the monotony....

dko

Are the heads being tested without the valve body or wired before installed on the body? If so, the heater switch's lever will get stuck above the piston preventing the piston from retracting and hitting the microswitch tab. The valve body prevents the piston from overextending

HVACNUT

Steamhead said:

Had a customer this afternoon where the end switch on one of these stuck closed, causing terminal 3 to constantly output 24-volts and keep the boiler running. 

If there's no call for that zone coming in on terminal 2, how is there 24 volts at terminal 3? 
Common is terminal 1, W from the thermostat is terminal 2, where does the 2-3 end switch go?

Steamhead

dko said:

Are the heads being tested without the valve body or wired before installed on the body? If so, the heater switch's lever will get stuck above the piston preventing the piston from retracting and hitting the microswitch tab. The valve body prevents the piston from overextending

No. They were on the valve body. I tested between terminals 2-3 with the voltmeter before hooking up power.

Steamhead

HVACNUT said:

Steamhead said:

Had a customer this afternoon where the end switch on one of these stuck closed, causing terminal 3 to constantly output 24-volts and keep the boiler running. 

If there's no call for that zone coming in on terminal 2, how is there 24 volts at terminal 3? 
Common is terminal 1, W from the thermostat is terminal 2, where does the 2-3 end switch go?



That must be for a different model. On these, common is 2 and comes from the transformer's R terminal. 1 is the other side of the heat motor coil from 2, and this goes to the thermostat. The other side of the thermostat goes back to C on the transformer.

The end switch on these is between 2 and 3, and makes contact when the motor opens the valve. Especially when working with electronic boiler controls, I run this to an isolation relay, which takes the 24 volts coming from 3 to close a contact which starts the boiler.

CTOilHeat

Did you try the heads on a different valve body?

I've seen the valve body stuck open making the end switch close and sending 24v off terminal 3.

You can usually free it up with a pair of channel-locks temporarily until you can change the valve.

Joe Mattiello

Hi
im assuming thermostat terminals 1, and 2 are not connected to thermostat to make sure it’s not a thermostat issue.
Are you checking continuity across 2, and 3 without wires to T, T terminals on boiler relay?
if this continues, after validating what I’ve asked, please contact Taco Tech support at 401-942-8000 and ask for tech support. 

JimP

Hello.

I’m very curious what you’ve learned about the cause of this phenomenon that you were called about. I’ve had situations where I suspected that a valve was “stuck “ and keeping the boiler and circulating pump on when none were calling for heat. The situation seemed to go away before it was a problem that would require some difficult diagnostics. These valves are in difficult to access locations. The twenty four valves and transformers are in three locations 50’ apart, 9’ high and above a drop ceiling. Years ago I custom made three indicator boxes showing the calling for heat status for each zone but not the #3 terminal status for each valve. This has allowed me to see potential problems.

This initiated a project to move the valves down from the ceiling into cabinets and upgrade the controls to the new Taco panels which show a call for heat along with the open/ closed status of each zone valve. That and the much cleaner wiring will allow easier diagnostics! Everything is installed and I plan to make the piping switch this summer.

Please let us (me) know what you learned.

mattmia2

something clearly built by someone who has never serviced anything

mattmia2

although i have run in to av installers that do this sort of thing and keep having what should be a 15 minute problem become a 4 month problem they had to fix yet still don't see a problem with not locating things where they can quickly troubleshoot them.

Steamhead

Will do. Haven't been back. For now I disconnected the trigger terminal #3 on that zone so it won't fire the boiler.

HomerJSmith

...causing terminal 3 to constantly output 24-volts and keep the boiler running.

You are always going to get 24V between terminal 2 & 3. This zone valve has two transformers. One transformer between terminals 1 & 2 and the aquastat transformer between terminals 2 & 3. The way to test for a stuck valve is to disconnect the TT connection to terminals 2 & 3 and test for continuity across 2 & 3. If for any reason the thermostat is calling for heat, the other transformer will cause the heat motor to move to a position closing the circuit between 2 & 3 turning on the TT. If you disconnect the wire to terminal 1, the valve should close breaking the continuity between terminals 2 & 3. If it doesn't you have a stuck valve.

Big Ed_4

The End switch is stuck closed . Could be too much amps though the burner control and fried the end switch points ..

HomerJSmith

Of course it could be pitting because of excessive current drain on closing. A small capacitor across the points would help with that. I wonder if putting a small disc cap across terminal 2 & 3 would help that. Hmmm

mattmia2

not so much with ac power

HomerJSmith

mattmia2, good point!