Need help installing new zone valves on an old Chromalox EDB-20-2 domestic hydronic boiler.

Denco

New taco zone valve does not energize the circ. pump contactor.

Hi,
I’m Denis & I have an old Chromalox domestic boiler that operated with Honeywell zone valves. I just recently figured out that the zone valves where causing my magnetic contactors to chatter & burn out. This is the 5th time in 25 years that this has happened . The 1st 4 times I had technicians repair the unit. They would install new magnetic contactors feeding the elements, charge me an arm & a leg & walk away. Some of the valves where also changed over time.


I knew that something exterior to the contactors was causing them to fail because those things are though so I did my own troubleshooting & discovered that the valves where the cause.

I ordered new contactors & also purchased new Taco 571-2 zone valves. It took me a while to figure out the wiring because the old Honeywell valves had 4 wires, 2 for the valve & 2 on the micro end switch & the Taco valves have only 3 wires.

The diagram for the Taco valve shows:
- a) One wire from the transformer that goes to feed the thermostat & continues on to # 1 terminal on the valve.
- b) The 2nd wire from the transformer goes to:
1):- the # 2 terminal on the valve & to,
2):- one pole on the circ. pump magnetic contactor.
- c) The 3rd terminal on the valve goes to the other pole for the circ. pump magnetic contactor.

I figure this to mean that & please correct me if I’m wrong; the #2 contact on the valve is common to the thermostat & the end switch feeding the circ. pump magnetic contactor.

Therefore:
(a):- When the thermostat contacts close, this completes the circuit from the power supply transfo, into the valve at terminal #2, out at #1, through the thermostat & back to the transfo. This causes the valve to open & closes the end switch inside the valve.

(b):- When the end switch circuit is closed, this energizes the pump’s magnetic contactor by allowing power to flow from the transfo to #2 terminal through the end switch, out terminal #3 , through the pump contactor & back to the transfo.

The pump magnetic contactor then energizes the elements magnetic sequenced contactors allowing the boiler to supply heat.

Well, nothing is ever easy!! It doesn’t work…..
The valve opens but the circ. pump magnetic contactor does not energize!

As is, the zone is operating because as stated before, the valve opens when the thermostat asks it to do so, but the pump contactor does not energize. So I've used a spare thermostat to feed the pump contactor. Therefore I have 1 thermostat operating the valve & the other one operating the pump contactor that feeds the heating element contactors. I didn't think it would help but I had also inversed the leads at the feeding transfo to no avail.

The thermostat I’m using is a Hunter Touch Screen Programmable. Model #44860 in heating only mode. I’m connected to terminals RH & W1.
Can someone help me?

Thanks
Denis Bourgoin
denismaringouin@hotmail.ca