On Wed, 06 Oct 2010 07:49:01 +0100 (BST), "Dave Liquorice"
wrote:

The microswitch is a bog standard Vsingle digit, and half decent
electronics supplier will have 'em. How ever it may not have failed.
The motor might not be opening the valve enough to operate the
switch.

Sorry to join in so late.

I know you are all talking about a different make but when I changed
my gravity fed system to a fully pumped one, I bought Horstman 2 port
valves from a well know seller of screws and fixings. I used 2 port
valves rather than 3 port valves because the latter seemed to be
criticised here.

18 months later, I had very similar problems to the OP: the boiler and
pump were not receiving any power from the micro switch. Like the OP,
I assumed the switch was broken. I never thought of stripping it to
see (I don't know how easy the Horstman ones are to open).

Perhaps you were right, perhaps it was not the switch but the
mechanism not moving the switch far enough. I can't be sure now, but I
think the switch did actuate when the valve was set to manual
override.

I bought new valves and I think one may have failed 6 months later!

I'll see how things progress but can face draining it down to fit new
valves as I'm sure that different makes of valve are different
lengths, so no doubt it won't be as easy as removing the Horstman ones
and dropping new ones in their place.

In summary, 2 port valves can fail the same way too.