Hi all,

I have a standard y-plan gas heating/hot water system. The hot water
works fine, but for the last six months or so whenever I switch on the
central heating it works for around ten seconds and then cuts out, with
quite a loud "clunk" seemingly eminating from the Honeywell V4073a
mid-position valve. After another ten seconds or so, the boiler
reignites and the same thing happens again, and so on...

I've discovered that if I slide the slider on the Honeywell valve to
the "Open" position, then the heating works OK. But I noticed on the
pdf data sheet for the valve
(http://content.honeywell.com/uk/home...21%20V4073.pdf)
that "Continuous operation of the valve motor at the fully Open
position is not recommended".

So my questions are these:

1. What is most likely to be causing the problem?
2. Is it safe/sensible to leave the valve in the Open position until
this is fixed?

I'd be hugely grateful for any help.

Duncan Clark