On Tue, 1 Nov 2005 13:49:40 -0000, "Set Square"
wrote:

In an earlier contribution to this discussion,
fagent3 wrote:

snip

In order to fit external timers to most combi boilers, you need timers with
volt-free contacts - where the contacts are completely isolated from
whatever drives the timer itself. You could safely use (say) a Honeywell
CM67 which is battery driven and definitely has volt-free contacts. It
doesn't do your +1hr in quite the same way as the Danfoss, but it can
achieve the same thing - and more - with its 'party' setting, and has lots
of other clever tricks up its sleeve.

I don't have a spec for the Danfoss FP715, but I suspect that its clock is
mains driven (with battery backup) and that the mains is switched through to
the CH and HW controls. If so, it will not be suitable for your purposes -
unless you use it in conjection with a relay.


Many thanks Set Square. I guess it's "volt-free" switching I'm after.

Am I correct in thinking that I'd need 2 CM67 units - to switch the CH
& DHW ? Although I called the Sime Super Fours a "combi-boiler" it
has a inbuilt hot water tank (40lt ?) and I' like to 'manage' both
from a new remote programmer/timer.

What is the "party" setting ? I'm not too bothered about the +1hour
but want some "advance" button where I can override the current
situation to on or off until it's next programmed on/off.

I read that the CM67 has radio-frequeny remote temp sensors, which
would be nice but not really suitable for me installation. I assume
that i can ignore the therostatic features of the CM67 and just use
it's timmed switching ?

However, since I'm likely to need 2 units - just what type of main
relays switches could I use to provide a similar volt-free switching
using the Danfoss ?

--
Hammy