In message , YAPH
writes
On Sun, 04 Oct 2009 21:29:56 +0100, geoff wrote:

Worcester 24Ri
Greenstar? Fit 0.47uF (275V AC X2 rated) capacitor across switched live.

Common problem John ?

Pretty obscure actually - it was about 3rd time calling W-B tech
support before I found out about it. Basically it seems the small current
passed by Honeywell-type mid-position valves (presumably by that 680K or
whatever resistor?) can fool the electronics of these boilers (and maybe
some other models? & other makes even?) into thinking they have
call-for-heat at their switched-live input.

The boiler I came across would jitter on an off with a relay inside
chattering away until it gave up and went into lockout. I'd changed the
motorised valve and W-B had been out and (as I recall) changed it again
before I eventually found someone there who knew of this issue.

I'd actually tried hanging a resistor across switched-live thinking that
might cure it and was quite surprised at the capacitor suggestion, but it
did the trick and the system's been sweet as a nut since then. Odd thing
is the system had been up and running happily for a couple of years before
the problem showed up (and it was one of my installs so I'm pretty sure
nothing had changed in that time).

Interesting reading

cheers


--
geoff