I purchased a house with a 3 zone heating system in it. Zones one and two work perfectly, the 3rd zone doesn't work right. First let me say, all thermostats are brand new, all zone valves are brand new (bases also), and the circulating pump is brand new. All parts are TACO.
When the thermostat in zone three calls for heat, nothing happens. Oddly enough, if you turn the thermostats OFF for zones one and two, and then throw the manual lever on the zone valve for the third zone, two minutes later the circulating pump kicks in and zone three has heat (that is with the thermostat still calling for heat). Throw the manual lever on the zone valve off (with the thermostat still calling for heat), and the pump stops.
My first guess would be the thermostat is bad, but that's why I put a new one in. Then i thought the top half of the zone valve was bad, so I replaced that. When it still didn't work, i thought a piece of the old zone valve might have falling into the base, so I replaced both the base and the top half of the zone valve.
Please, any help with this would be great!