I had a radiant heating system installed just over two years ago (Munchkin boiler to radiant baseboards). I have had 3 failed zone valve actuators during this time. They were all the Caleffi Z-one Z151000 model. The mechanism continues to work (it opens the valve when the thermostat tells it to), but the boiler doesn't fire up, which leads me to believe some electronic part in the actuators has failed (it doesn't seem to be passing on the message to the boiler to start up). I know it's a problem with the actuator and not the boiler because when I replace the actuator with a new one, everything is back to working as expected.

I'm wondering if anyone else has had a problem with these actuators? Or if not, any ideas why they might be failing?

There's no clear pattern in the failures: 2 failed right at the beginning of the heating season (after being off for several months during summer); the third one has just failed mid-season.

The installer has said that there is a 2-year warranty on these actuators, so I'm pretty much SOL as far as they're concerned. (Actually, I may be able to get them to replace the one they installed last year, since it should still be under warranty.)

Second question: To replace the actuator it is easily removed from a brass fitting that (I assume) contains the actual valve. Is this brass valve fitting standard, or will only the Caleffi actuators fit? (In other words, I'd like to try a different brand of actuator without having to drain the system, cut out the valve, re-sweat a new valve, etc.)

Here's the actuator: