On 2007-12-25 12:20:42 +0000, said:

On 25 Dec,
"Roger Mills" wrote:

A 3-port valve is used by Y-Plan systems - and also enables you to have CH
or HW, or both together. It's main disadvantage is that the valve actuator
plays a more strategic role in the overall control of the system than other
plans, and is more complex than a 2-port actuator, and prone to failure,
causing the whole system to stop working.

Agreed, the microswitches regularly fail.

It also limits you to 2 zones so you can't, for example, have separate
upstairs and downstairs heating zones in addition to hot water.

Untrue, I had 3 zones with 3 port valves with a (modified) Y plan system (the
supplier was out of 2 port valves when the system was installed).

With S-Plan+ systems you can have as many zones as you like.

You could with Y plan, but it gets complicated and unreliable.

I've converted to S plan. It has been much more reliable since. With Y plan I
had to change microswitches at least annually. I don't think I've had a
failure in the 5 years or so with S plan.


Which seems kind of odd, because the motor units are similar and there
would be as many operations as before.

However, I agree with you. A system that I installed many years ago
was fitted with two port valves because that seemed to be a better
design decision. No failures. On the one that had been installed
in the current house as original, there was a three way valve.
These would fail about every 3 years or so and not always at the
obvious times of the start of the heating season.

When I renewed the system, I switched to using 2 port Honeywell valves.
I also fitted 28mm versions for the main ones to reduce flow
restriction and 22mm ones in smaller zones. No problems at all with
these in 5 years, although the boiler does have an automatic valve
exercising function.