Replies

1. Expert Member
   Akos | Nov 25, 2019 02:29pm | #1

   The way I've done this is to use the end of travel switch on the zone valves. You put all the end of travel switches in parallel and connect it to your pump relay.

   Each thermostat drives its own zone valve, but if any of them are open the pump turns on.

1. 
   user-7586704 | Nov 25, 2019 03:22pm | #5

   I’m not using zone valves. I have 3 thermostats monitoring different areas of my hydronic system. If any stat hits its preset value I want the relay to power the single circulating pump

2. 
   Jon_R | Nov 25, 2019 02:38pm | #2

   One could use diodes wired to a relay to get the desired "OR" logic.

   Pure speculation, but perhaps some smart pumps are smart enough to realize that no zone valves are open and not use any significant amount of energy even when left on.

3. 
   josh_in_mn | Nov 25, 2019 02:48pm | #3

   You want something like this:
   https://www.supplyhouse.com/Taco-SR503-4-3-Zone-Switching-Relay

1. 
   user-7586704 | Nov 25, 2019 03:20pm | #4

   But that relay has 3 independent zones with a high voltage output for each

1. 
   josh_in_mn | Nov 25, 2019 04:04pm | #6

   Whoops, this one instead.
   https://www.supplyhouse.com/Taco-ZVC403-4-3-Zone-Valve-Control-Module-with-Priority

4. Expert Member
   BILL WICHERS | Nov 25, 2019 07:06pm | #7

   Thermostats usually use 24 volts AC for signaling, so you can’t use diode logic.

   You really don’t need anything special to so what you want to do here. I would just use three relays. Use octal base relays so that you can easily replace them if needed. Connect the coil of each relay to one of the thermostats so that each thermostat controls one relay. Connect the normally open contacts from all three relays in parallel. Connect the paralleled contacts to run the pump.

   In this way, when any one thermostat calls for heat, it closes one of the relays which activates the pump. If multiple thermostats call for heat, you just have several relay contacts in parallel so the pump runs and there is no conflict. The pump stays running until the last thermostat stops calling for heat and opens it’s associated relay. You can add as many relays as you need for multiple zones. You can also use relays with additional contacts if you need to expand the system to do multiple things like both run the pump and operate a zone valve, for example.

   No special or fancy equipment is needed, and relays are simple, reliable, and easy to understand and fix, if needed. Grainger is a good source for the relays and sockets. You might want to get a piece of DIN rail to mount the sockets on and a Hoffman box (or similar) to install them in. If you mount the relays using sockets on a DIN rail in a metal enclosure with a hinged lid you’ll have a very nice professional installation.

   Note that it’s nice to have a pilot light on each relay so that you can see which thermostat(s) is(are) calling for heat at any given time if you are testing things.

   Bill

1. 
   Jon_R | Nov 25, 2019 11:03pm | #10

   >Thermostats usually use 24 volts AC for signaling, so you can’t use diode logic.

   If AC, then it takes 4 diodes as a bridge rectifier on each input, producing a DC "OR" output.

5. 
   tommay | Nov 25, 2019 07:19pm | #8

   If you hook up each of the two leads from the three thermostats to the t-stat connection on your pump relay, no matter which one of them is calling / closed, it will turn the pump on. I think that is what you are looking for......

6. 
   walta100 | Nov 25, 2019 10:48pm | #9

   I must be missing something. It sounds like you are asking to have 3 different thermostats that will turn on the same pump. The system has no electric zoning valve. So when the pump is running all 3 rooms get more heat.

   If I understand correctly it seems like when you are too hot you will need to run all over the house turning down thermostats to shut down the system.

   It seems to me you really want one thermostat with 2 remote temp sensors that controls the pump in response to the average of its 3 inputs.

   Walta

7. Expert Member
   NICK KEENAN | Nov 25, 2019 11:18pm | #11

   If you have one pump and no zone valves, you have one zone.

   It's easily possible to control one zone with three thermostats -- just wire them in parallel -- but somehow I suspect that's not really what you're trying to do. Most likely, one of the three spots will consistently be the coolest. That thermostat will control the system, the other two will never call for heat. You'd get the same effect from just having a single thermostat in that spot.

   It used to be common for single family homes to have a single thermostat for the entire house, the conventional wisdom was that the thermostat should be placed in the coolest conditioned spot in the house.