On Wed, 17 Aug 2016 10:00:24 +0100
"Dan S. MacAbre" wrote:

Roger Hayter wrote:
Dan S. MacAbre wrote:

Dan S. MacAbre wrote:
My mum and Dad's boiler wants to stay on all the time. I thought
the best thing to do, besides just switching it off for now,
would be to try and work out how it's all wired together, and
then work out possible causes. I've only so far had time for a
quick look, but something has struck me as odd. They have two
motorised zone valves, but there is no room thermostat anywhere.
I'd always thought that each zone valve responded to a
thermostat. Is there any valid configuration that has two zone
valves, but no room thermostat?

Well, I've had the floorboards up, and made a few drawings, and I
think I've got my head round it now. There is no room thermostat
- the timer output for the CH goes straight to activate the
motorised valve, so it's basically acting as a relay. I can
understand this if the timer output is not capable of driving the
pump and the boiler; however, it's a mechanical timer, so I don't
think it's /that/ delicate :-)

snip

It also ensures that the boiler does not light until at least one
valve is open. A few seconds might not matter for an old,
relatively massive boiler, but it could be harmful if the valve
actually failed to open at all.


I was thinking more of not having the valve at all, since it's wired
direct to the timer (and at first I thought it must always be open),
but then I realised that you can't then have the HW timed on by
itself. As usual, these things make more sense when I've had a
chance to think about them :-)


I would suggest that you study some of the standard Plans, C, S, etc,
and see which of them most suits your setup, with an added Room 'Stat.
Then use the best one as a guide to how you rewire yours. The design
work has been done already, what you have to do is select the best
implementation of this work.

--
Davey.