Christian McArdle wrote:


This is one of the reasons why unvented cylinders must be installed by a
trained competent person.

The zone valve you are looking at is the safety override valve that was
supplied with the cylinder. You must not interfere with it in any way. It
should be lashed up to its own dedicated overheat stat. It is the equivalent
of an immersion heater's overheat stat.

What you need to do is add an additional functional zone valve to your
S-Plan-Plus system. This should be run from your programmer, through a
separate thermostat and with the boiler interlock connections used. The
unvented cylinder is, thus, separated from the boiler by TWO independent
zone valves.

I was looking at the wiring diagram from the manual of the cylinder
which shows the wiring diagram for an S-Plan using the valve from as a
normal zone valve.

I would have thought that using it in this way would be safer than it
currently is (I.e. if the power failed to the current zone valve the
boiler would continue to heat it up - if it is on the same circuit as
the boiler then it the zone failed - the boiler would also fail)

I agree an extra zone would do the same thing - but then you have 2 x
zone valves - is this really necessary? You also say 'through a
separate thermostat' - but there is no mention of this method in
the manual?

Is it 'normal' to have 2 zone valves on an S-Plan with an unvented
cylinder?

Thanks for any help