In an earlier contribution to this discussion,
raden wrote:

In message , Set Square
writes

3-port mid-position valves have an inherent weakness in that they
rely on microswitches in the actuator to control both the valve and
external parts of the overall system - inluding switching boiler and
pump on in CH-only mode.


I don't think I've ever come across cam wear in an actuator head in
the (high) hundreds which I've repaired in the past

The most common problem is synchron motor failure - they all use more
or less the same motor (although there were some better quality ones
in the past

The second most common fault is contacts burning on the microswitches
(again in the past some actuator heads used larger microswitches)

The other common problem is weak return springs


I bow to your superior experience in dealing with hundreds of the things.
The few I've taken to bits have had rather wobbly cam plates (as opposed to
worn cam surfaces per se - perhaps my description could have been better).
However, the effect is the same - if the switch doesn't operate for whatever
reason - or if the motor fails - the HW/CH system doesn't work properly.
--
Cheers,
Set Square
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