taco zvc404exp thermostat light on zone valve light off

dylancasey

Noticed radiators in room were warm and thermostats was off. Inspected the valve and suspect it was completely closed. Then I turned on the thermostat (yellow light for tstat cones on) and the valve opened...kind off...but the zone valve light (red) didn't come on and the boiler and pump didn't turn on.

I suspect I have a bad zone valve that won't close all the way and when the Tstat calls for heat the valve is not activating the switch to turn on the boiler and pump. 

So will replacing the valve fix both not closing all the way and when turned on, activating the boiler and pump?
thanks
Dylan.

update: I am now getting both zone and thermostat lights to come on and the valve opens. The main issue is that when I turn off the thermostat the valve doesn't close all the way. Assume the motor needs to be replaced?

Joe Mattiello

hi Dylan
thanks for reaching out through Heatinghelp.com, great resource for help with any heating systems. there are a lot of knowledgeable people that frequent this site.
the yellow light, I'm assuming is on the ZVC control board indicating a demand? love that control!!
if yes, and the valve is opening on demand, but not firing the boiler, you can jump out terminals 3, and 4 on the control so the boiler will fire when the thermostat calls for heat. 3, and 4 on the control simulates end switch closure to engage boiler. if the valve doesn't close all the way, and you have ghost heat, you may have to replace the zone-valve head. usually those heads are robust, and don't fail unless someone bench tested the valve without a positive stop to stop the piston from over extending. Before changing the valve, don't rule out the thermostat as the culprit. if you remove the thermostat, try putting the two wires together to see if the boiler fires, and shuts off when you pull the wires apart. I guess what I'm saying, is do some diagnostics before condemning the valve. for further assistance, I would reach out to Taco Tech support at 401-942-8000. there are some pretty knowledgeable technicians just waiting for your call. they are a lot more knowledgeable then me:) hopefully this was helpful.

dylancasey

Thanks @Joe Mattiello . Today I found that when the thermostat calls for heat the thermostat (yellow) light and zone valve (red) light come on, the valve opens, the pump goes on, the boiler lights...so all working as intended. The problem is when I turn it off...the valve doesn't close all the way.

I may not be using correct terminology.

Given the current scenario would changing the "motor" that opens the valve solve the not closing all the way problem? or is it likely my issue is with the valve itself from a mechanical perspective? Note, the motor appears to be old and I did notice most of the other motors have been replaced.

Thanks
Dylan

Zman

Does it happen to be a Honeywell valve? They have tendency not to prove the end switch as they age.
In some systems, where there is no risk of "deadheading" the circ, you can simply jump the end switch terminal on the Taco and the problem "just takes care of itself".

Zman

Most Zone valves have replaceable power head which is a pretty easy swap.

dylancasey

@Zman yes, it's a honeywell valve. Again , the problem is that when it's turned off, it won't close all the way. The motor turns but it doesn't close enough to stop the water flow. The boiler and circulating pump turn off as expected as well.

My question is: will replacing the motor on the valve resolve my problem? ie. could the motor be so old that it's not allowing the valve to close all the way?

Zman

Pull the power head off and manually cycle the valve. If it will close that way, you just need to replace the power head. If it won't, you will need to replace the guts. You will need to get into the inside and rebuild. You will need to drain down but should be able to keep the valve body.

dylancasey

Copy that