On Wed, 17 Dec 2003 10:05:48 +0000, Set Square wrote:

In an earlier contribution to this discussion,
Andrew Gabriel wrote:

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.

Ah, I see! You're talking about the by-pass loop rather than the wiring. You
are perfectly correct - the Honeywell schematic doesn't show a by-pass loop
and ought to do so.

My point is also valid. The Honeywell electrical diagram shows the boiler
and pump feeds connected togther - so that the pump stops when the boiler
demand is turned off. For a by-pass to work, the pump needs to be controlled
by the boiler so that it can continue to run after the boiler has finished
firing.

It all depends on the boiler.
In my own home the bathroom towel warmer is the bypass.
On other systems I have doen with S plan I have used a boiler that does
not require (an external) bypass.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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