Two zone heat in 2 family house, where to wire thermostat upstairs ?

Question

I recently purchased a 2 family house, house is divided upper and lower (1st floor is 1 fam and 2nd floor is 2nd fam). Anyways, there are two seperate circulator pumps, one for upstairs and one for downstairs. The wire from the upstairs thermostat was cut off at the boiler at some point before we purchased this house. Now that we have made repairs and restored the second floor , we cannot figure out where these thermostat wires for the second floor should go into .... the solenoid attached to the boiler ?
The solenoid appears to only have inputs for 1 thermostat which is ours on the first floor. With those inputs taken up by our thermostat where in the world should the upstairs thermostat be wired to ? Any help is appreciated.

Answer 1

This one is a little tough to answer based on the information given. If you have a true two zone system then the thermostats should start and stop the individual circulation pumps and the boiler should start and stop based on the water temperature of the boiler. In other words, the boiler temperature is set by limit switches so there is always hot water in the boiler similar to a hot water tank. You may need to have a technician look at the wiring of the furnace.
Have a look to see if there are any contacts for starting the circulating pumps. The previous owners may have made changes ot the original wiring. Also check the position of any valves on the output side of the 2nd floor circulating pump. They should be open.

Answer 2

one of the thermostats must not have been fitted, because if the two were connected this would enable the system to be fired up by either party but if one thermostat is turned off the other would still keep the boiler running. I don't know how you could split the system, as the boiler would be working overtime. Is the system gravity fed, i.e has it got a cylinder header tank ( this is a tank possibly in the loft area ) Does it heat the domestic hot water. Are both pumps connected to the boiler. Even the three way valve is governed by the boiler as the boiler can only sense the signal from the thermostat. We at present don't know how this has been connected without a conflict between the two.......if this is a UK system.