3 zone boiler heat, one zone is too hot
Well, we know water's getting through &amp; the circulator's pumping. So, I'd say get an HVAC guy out to inspect, test &amp; replace whatever. The valve actuator motor could be failing &amp; getting stuck. Meaning, you're periodically getting heat when another valve opens &amp; pumps. Or, the valve's circuitry has an intermittent problem with not signaling the valve to close or the circulator to stop. I don't think there's a rebuild option here, sorry. Plus, you'll know what's what when the other valve's go.