On Fri, 29 Apr 2011 13:39:07 +0100, fred wrote:

Say only have boiler 2 on when the return temp is below a certain level
or in combination with an outdoor temp stat? Simple relay logic control
could manage that.

I think we're going round in circles here - I originally muttered that I
was thinking of using an outside stat to determine when to bring the 2nd
boiler in with the 1st!

Watch out for over complexity and maintainability, I am reminded
occasionally of this when kind people ask who would maintain x, y & z if
I got run over by a bus tomorrow. The answer is universally, "I wouldn't
give a f'ck" but you may be more concerned :-).

Indeed. That's rather the situation I'm in now: seems whoever designed
(or perhaps "designed") the original system didn't leave (or have :-))
much clue as to how it was supposed to work so I'm trying to work that
out now from what I can see.

--
John Stumbles -- http://yaph.co.uk

Men are from Mars, Women are from Venus and Pop Psychologists are from
Uranus