Thermostat or zone valve control problem?

Swamp_Yankee

I’m having a problem with one of my zones staying closed when it shouldn’t be intermittently.  Every so often the thermostat should be calling for heat (room temp below the set point) and I’ll go down to the zone valve control and the corresponding lights to that zone are not lit on the control box and the zone valve is closed.  How do I troubleshoot to isolate the problem, ie: is the thermostat not actually calling when it should be or is the thermostat calling and the control box is not in turn telling the zone valve to open?

Alan (California Radiant) Forbes

What kind of control box do you have? Taco? Caleffi? Argo?

If the control box is working properly and the light that shows thermostat closure doesn't come on, then the thermostat is bad. What model thermostat?

bburd

Or possibly a bad connection or intermittent open wire in the thermostat circuit.