Colin Forsyth wrote in message
...
OK several issues


I also have two pairs of Flow & Return manifolds for Upstairs & Downstairs
radiators, would this lend itself to two zones ? How do I cater for that
?

For starters, don't use a 3-way valve - use individual zone valves. In your
circumstances, I would use 3 - one for hot water and one each for upstairs
and downstairs heating.

Each zone valve would be controlled from the programmer and would have its
own room or cylinder stat, as appropriate. Each valve has an independent
pair of contacts which close when the valve is fully open. These are all
connected in parallel to switch the boiler and pump - so that the boiler and
pump only run when one or more zones are calling for heat. It may make sense
to use programmable stats for the two heating zones - so that you can have
them on at different times should you so wish. The main programmer would
then control the hot water on a timed basis, but would have heating switched
to continuous - leaving the actual control to the programmable stats.

As someone else has explained, with this arrangement (zone valves rather
than 3-way valve) you will need a bypass loop in order to ensure that the
water always has somewhere to go when the boiler over-run stat decides to
keep the pump running after the boiler has stopped.

Roger