"Sam" wrote in message
...
On Thu, 10 Jan 2008 16:05:49 -0000, "Roger Mills"
wrote:

The actuator of a 3-port valve has more components (extra microswitch,
diode, etc) than the 2-port equivalent and is more prone to failure. Mine
last about 2 years on average.

That's not very long. It's not very reassuring.

On the other hand, we've been in our house for 18 years and the 3-port valve
is still working fine.