In article ,
"Set Square" writes:
In an earlier contribution to this discussion,
Andrew Gabriel wrote:

You will need to allow for pump overrun with most boilers.
The Honeywell schematic does not.


This is true. In fact, it's only a small change from the Honeywell diagram.
The basic logic remains the same, but the output from the zone valves'
volt-free contacts drives just the boiler rather than the boiler and pump in
parallel. The pump is then connected to the boiler's pump control terminal -
which is live whenever the boiler is firing plus whenever the boiler's pump
over-run stat calls for circulation to continue.

That's not the problem. The problem is that when the last zone valve
closes, there's no water circuit for the pump overrun. You have to
make some provision for that.

--
Andrew Gabriel