Zone valve not closing

[Ragnar]

I have a series of taco E075C2-1 zone valves and one of them appears to stay open even when the system is not calling for heat. The motorized valve appears to work fine when the thermostat calls for heat and no heat. However, the radiators never completely cool down. And the temperature in the zone continues to rise slowly. I touched the supply pipe to the zone and it is very hot. The return is warm. The pump is not running. Therefore, the control system seems to be working just fine, its just that the valve is not completely closed.

The taco valve is said to be "smart", in that it has a sensor and knows how much to turn the valve to open and close it.

I've concluded that either the motorized valve is not sensing the close position correctly or the actual ball valve is not fully seated in the closed position. My question is, which is more likely to fail and should I replace first? Also, how do I tell if the ball valve is in the closed position?

Thanks

 

[Armo74]

Sounds like the valve is letting by that is a good Indication that the valve isn't seated properly. It could have some system debris lodged in it not allowing it to seat properly.

 

[Ragnar]

That's what I was thinking. Guess I'll just replace it and see if it fixes the problem.