Taco 570 ZV fail

kcopp

I ran into an issue today w/ a Taco gold head zv. Customer complained about over heating in one zone.
Thermostat was off... still got heat.
Arrived and found the 2nd fl zone valve not open but the boiler running and the circulator on... dead heading in effect.
Pulled the thermostat off the wall...still runs.
Changed out the Zone valve head problem solved...
I have seen plenty of failures where nothing works...but this?
Valve was older early 90's
The really odd thing is that the "ghost flow" was on the return side backing up to the 2nd fl.
Anyone had this one before?

STEVEusaPA

Did you autopsy the head? Were 2 & 3 closed despite being de-energized?

Tinman

Failed part autopsies are the best.

Joe Mattiello

hi
sorry to hear about your zonevalve issue. apparently the end switch terminals 2, and 3 were forced closed for perpetual demand. normally, it's a thermostat issue with a closed switch causing the demand, but if end switch interfaced with pump relay, and boiler forced closed, yes everything down stream will operate. did anyone remove the head and bench test it when not attached to base? If yes, that will result in the shaft over extending and it might not correct itself. these valves are not designed for bench testing without a positive stop; valve body.
sounds like you were able to replace the valve head which was approximately 30 years old, so it's not under warranty; joking of course. it's really a well engineered product that works with thermal expansion of the bees wax to push down on the piston with it's conical shape to trip the paddle switch after approx 1.5 minutes. not sure if I can help further, and if you do need additional support, please reach out to the lonely tech support team at Taco 401-942-8000 they are always ready to answer these difficult technical questions.

EdTheHeaterMan

To answer your Ghost Flow Query... if there is a higher temperature in a pipe that is lower (like in a basement) and there is a vertical riser that comes off the pipe, there is a chance for the warmer water to slowly rise up the center of the pipe while cooler water near the outer edges of the pipe slowly creeps downward. This is the ultimate Ghost Flow problem that confounds the best of us. Water moving two directions in the same pipe. The larger the diameter the greater the chance.

So the fact that the boiler was staying so hot and cycling off the limit, and all the valves were closed, (assuming the valves are on the return) the hot supply manifold will allow hotter water to rise to the second floor and cooler water to fall back to the boiler in the one supply pipe.

If the valves are on the supply, this can also happen in the returns since the circulator is deadheading and also generating heat, the expanding water with no flow will force heat out of the boiler thru the return.

This is from page 12 in this text from B&G http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf Dan H was the author but it belongs to B&G

Canucker

I vaguely remember @Mark Eatherton showing pictures of an old system designed to support gravity flow using a single pipe. I may be misremembering but I thought it was odd at the time

kcopp

I still have the valve.
I didn't bench test it.
The line on the return is 1" copper that splits into 2- 3/4" loops.
I am not disappointed that a 30 yr old valve failed... it worked well for a good amount of time.... I was just surprised that it failed the way it did.