3 zone valves and one circulation pump conflict

hellovn

Hi All,

Due to Covid, I just found a weird behaviour with my 3-zone hydronic oil boiler. My system has 3 taco zone values with one circulation pump.

As both my wife and I are working from home now, we set a schedule for the main floor to be 21C and the upstairs to be 15C from the Ecobee thermostats. In the morning, the main floor zone is still running but the upstair zone stopped due to it is set to 15C. When the upstairs zone is set to 15C, it sends the signal to the circulation pump and stops the pump. As my main floor zone is open and the circulation pump is stopped, the heat never goes to 21C.

I have to reset my main floor thermostat (set it to 15c and back to 21C) for the circulation pump to run again.

I could change the thermostat schedule so that it won't happen again but just curious if this flaw could be fixed from the boiler system?

Thanks.

hot_rod

Has something changed recently, new t-stats? rewiring?
The Ecobee should open the zone valve, then the valve turns on the circ. Any valve, any combination.
Are you wired through a relay box?

hellovn

Yes...I use the fast stat common maker for 3 three Ecobee thermostats. Maybe the Fast-stat relay is the root cause?

hot_rod

Ecobee has good tech support and wiring examples at their site.

hellovn

My question is: is the behaviour expected? One zone could turn off the heat and the circulation pump and affect the other zone if they share the same circulation pump?

hot_rod

hellovn said:

My question is: is the behaviour expected? One zone could turn off the heat and the circulation pump and affect the other zone if they share the same circulation pump?

\
Nope, that is why you have 3 thermostats and 3 zone valve, for individual control.

hellovn

But 3 zone valves share the same circulation pump? I checked my Aquastat wiring and I don't think we have a way to wire the 3 zone valves with one circulation in parallel. It seems they are wired serially now.

Jamie Hall

The end switches of the zone valves should be wired in parallel and power the circulation pump. They may -- or may not -- be all wired in series with the aquastat, so that the pump only runs when the aquastat is happy. The aquastat may also control only the burner.

If need be, that circuit could power a relay which, in turn, powers the pump.

All this has nothing to do with the thermostat wiring. The thermostats should control the zone valves.

hellovn

I think your answer may give me some ideas. I need to find a way to re-wire my end switch wiring (2 red wires) so that it only turns off the circulation pump when all three zones are off.

Jamie Hall

hellovn said:

I think your answer may give me some ideas. I need to find a way to re-wire my end switch wiring (2 red wires) so that it only turns off the circulation pump when all three zones are off.

Or, to put it another way, that any one of the three will turn the circulation pump on. It's "or" -- parallel -- logic: ZV1 or ZV2 or ZV3 turns on the pump.

EBEBRATT-Ed

@hellovn

You said you have Taco valves. The Tacos are three wire zone valves with the thermostat wiring intermingled with the end switches. Easy to get confused with polarity etc on those. Just saying

hot_rod

A pic of the valves, relays and wiring may help, there are different types of Taco valves out there.

HomerJSmith

If the Taco ZVs are model #556-561-571, you may need an auxiliary transformer.

Terminal #1 from each ZV is connected to the W on the controlling thermostat. The R on each controlling thermostat is connected to the hot lead on the transformer, normally the R transformer connection.

Terminal #2 on each ZV is connected to one of the T connections on the aquastat and also to the C connection on the Transformer.

Terminal #3 on each ZV is connected to the other T connection on the aquastat.

I think I remember this correctly.

Charging an Ecobee is easier with a 3 or 4 conductor thermostat cable.