Explain This Relay!

laykelane

Hello! Licensed plumber dipping my toes into the boiler repair world so bare with me.

This call i was at today had two bad zone valve heads, which I replaced and the problem went away. Typical residential 2 zone system. Simple enough, but wanted a better understanding of how they were wired, as it was not the same as the wiring diagram showed.

The house has two zones but at some point, for some reason the zones were tied together to operate off a single thermostat.

If you look at the pictures, someone had installed a 90340 relay that the zone valves are wired to and am just curious what it’s doing, and why it’s there.

The zone valve heads only had two wires going to each instead of three, like the diagram shows. Any ideas? Just trying to understand! Tia!

mattmia2

you'd have to trace it out and draw it to figure out exactly what they did, but if the zone valves only have 2 wires, either the thermostat is controlling the boiler and circulator and that relay is is in parallel with the boiler and controlling the zone valves or the t-stat is controlling that relay and the relay controls the zone valves and the boiler and circulator.

the way it originally was is something like this:

the zone valve has an end switch that closes when the valve opens. that allows a separate thermostat to control each zone valve, then the end switches on the zone valves can be paralleled together and control the boiler and circulator so if any of the thermostats calls and opens a zone valve, the end switch will fire the boiler.

EBEBRATT-Ed

My guess is similar to @mattmia2

I would guess they went to 1 stat for whatever reason so the stat would open both valves and pull in the relay coil. The relay contacts would act as the end switch and fire the boiler. Not exactly right but I guess it works.

The boiler and circ shouldn't run until the valves open but with no valve end switches(s) it can't be done

laykelane

thanks guys appreciate it!