Resistor on Taco Zone Valve

John G. Merritt

Hey fellas!

Why would a Resistor be installed on a Taco Zone Valve Between #1&#2 Terminals? Had a clock thermostat on that zone. I was told it prevents feedback. How?
What feedback? I don"t understand this.

John

buss

resister on zone valve

the resister allowes a complete circuit to bypass the zonevalve that cycles on and off. The current is needed to run the clock

John G. Merritt

Still do not understand it!

Sorry, but I still do not understand the resistor being installed between 1 & 2 on the Taco Zone Valve!
I don't understand the feed back thing.
Sometimes I just don't get it. Need a clearer explanation.

John

Bill Clinton

resistor

The resistor was installed to benefit the electronics of the t'stat. The thermostat has no batteries, so it needs to "steal" some current from the operating circuit, only a volt or so and very low amperage. So, it bypasses the switch that sends full power to open the valve and gets what it needs, and sends the rest down through the heat coil of that zone valve. This works fine until there is a call for heat and that taco valve opens. When the valve gets near full open, it interrupts current by opening a switch, so the heater coil doesn't overheat. Now the electronics have no circuit, so the thermostat goes into power-failure, shut down mode which has a capacitor to supply juice to maintain memory, but not operate other functions. The valve closes and restores power and after sulking for a while, the t'stat operates again. The valve opens, breaks the contact, and the t'stat shuts down again.
Etc.

The resistor gives current a path to go when that switch is open. It draws a couple of watts continuously, even when no heat is required.

Of course, the simple solution is to either use a battery powered thermostat (immune to power surges also), or another type of zone valve that doesn't interrupt current.

This little lesson cost me a number of hours of call-backs a number of years ago.

Bill

John G. Merritt

Think I've got it!

Thanks Buss, Bill.

I think I've got it now.

John