Fried Taco ZVC 406 EXP - over easy

Alan (California Radiant) Forbes

We installed a Taco zone valve controller 6 years ago; has worked flawlessly until I get a call from the owner that there is a burnt electrical smell in the boiler room.  The culprits are some components in the controller have melted (see photos).



But before I replace the controller, I'm thinking that maybe one of the Danfoss thermal actuators has shorted, so I ohm them out.  All of them save one have numbers around 130 ohms, except this one that comes up with a decimel number  .132.  When something like this shorts, do the numbers get this low?

Ironman

Shorted

Alan,



That's virtually no resistance. I'd say it's toast.



If you want to confirm, hook the actuator directly to a transformer with a 1 amp fuse in line. Then amp it when power's applied. Should be 5va or less (va = volts x amps).



Obviously, you need a sensitive enough meter or wrap the wire 10 times around an amprobe jaw and divide the reading by 10.



Was the burnt relay on the zone that the suspect actuator is connected to?

Alan (California Radiant) Forbes

Bob

Thanks for your reply.



The blown component is on a different zone which doesn't make sense, but I'm grabbing at straws here.  I'll replace the actuator and hope for the best.