I have a gas fired, forced hot water heating system with 3 zones. The zones are controlled by a TACO switching relay (SR506). I would like to add a 4th zone. That is relatively simple. I can add the circulating pump, etc. and can easily connect the new thermostat. But I do not want a thermostat on the new zone.

:confused: My question is on wiring.:confused:

I would like to have the 4th zone activated when any of the other 3 zones call for heat. In other words, if zone 1 calls for heat, zones 1 & 4 will run. If zone 2 calls for heat, zones 2 & 4 will run, etc.

Does anyone know how I can wire the thermostats and/or circulating pumps to get the reults I am looking for.

Thanks.

So you have 3 circulating pumps now?

Yes, 3 pumps are working now.

At first thought, it seems if you tie the other 3 pump relays to the coil of the fourth, they are going to back feed and all 4 are going to run unless you pile relay on relay. (Labman distrusts relays.) Perhaps have the white wire that fires the boiler also start the fourth pump. That way, any time one zone starts the boiler, the fourth pump starts.

That sounds like it might work. I would jumper the XX leads to the TT connection of the 4th zone thermostat. The only question I have is what would the 24 volt from the XX end switch/boiler do to the SR506? Since the SR506 is a relatively expensive box, I'm a little nervous about that.

Based on your input, I had a thought. What if I front end the SR506 with another box? Is there a box that accepts 3 thermostats and has one boiler end switch? I do not need the line voltage to the circulator pumps in the additional box. I would wire all the thermostats to the front end box and jumper to the corresponding zone TT connections on the SR506. I would use the XX end switch that would normally go to the boiler and connect it to zone 4 TT on the SR506. If any zone calls for heat, the front end box will activate the XX and zone 4 will start along with any of the other zones.

Here is an update. I connected the XX switch to the zone 4 TT. The problem is I got continuous heat once it turned on. It never shut off.

Instead of buying another box at $150+, I took another approach. I discovered the ZR line voltage terminal gets activated when any zone calls for heat. I disconnected the hot lead to the zone 4 circulator pump and reconnected it to the ZR terminal. I left the factory installed jumper in place between the ZC and ZC terminals. Zone 4 now heats the space whenever zones 1, 2 or 3 call for heat.