"For Q2 M8" wrote in message
om...
"Roger Mills" wrote in message
...

If you can clarify this, we can determine what is or is not possible.

Roger


OK, more info...

The temperature sensor is strapped around the hot water cylinder, it's
a Honeywell L641A1005
it has a white wire that disappears under the floorboards in the
airing cupboard
(might have to rip some up and have a look)

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I' had a look inside the controller and the model was marked as ST699B
http://www.grantandstone.co.uk/heati...rols/st699.htm

If I slide the lower switch (Hot water) to "CONT" then I have hot
water (after about 20 minutes)
If I slide the middle switch (Heating) to "CONT" then I get CH & HW

Tech Info:
http://content.honeywell.com/uk/homes/catalogu.htm

http://content.honeywell.com/uk/home...10%20ST699.pdf

It does not have a wire for CH OFF (connector 4)
So does that mean I have a "sundial Y" plan ???


User manual
http://content.honeywell.com/uk/home.../st699user.pdf
from:
http://content.honeywell.com/uk/homes/manuals.htm

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I'm still not quite sure whether your system is gravity or fully pumped.

Join the club

I've checked and I don't have an electrical immersion heater. Guess
you could have both... ?
Don't know why you would, but I haven't.


The boiler has 3 pipes:
1. thin (approx 10mm) pipe - marked "gas"
2. thick (approx 22mm) pipe - goes to the water pump then up into the
airing cupboard
3. thick (approx 22mm) pipe - goes up into the airing cupboard

pipe 3 appears to have a drain tap on the end of it - is that for
draining the central heating ?

Many thanks,
Sam.

OK - I think we're getting somewhere!

The fact that there are only 2 water pipes going to the boiler - one of
which is in-line with the pump means that you have a fully pumped system.

The fact that the tank stat is electrical, and has a cable which disappears
under the floor almost certainly means that there is a zone valve (or
possibly a 3-port valve) hidden somewhere under the floorboards.

At some point between the boiler/pump and airing cupboard both your flow and
return pipes MUST split into two circuits - one for hot water and the other
for heating. On the return side, this is probably just a T-piece. On the
flow side, it is either a T-piece with a separate zone valve on each output
or a 3-port valve which incorporates the T and the zone control in one unit.

You have almost certainly got either an S-plan system (2 zone valves) or a
Y-plan (3-port valve). See http://content.honeywell.com/uk/homes/systems.htm
for details.

Either way, you appear to have the capability of controlling hot wat and
heating separately *including* having heating without hot water - provided
that it is wired correctly.

BUT, if you want them both to be timed but at different times from each
other, you need two independent timers - and the ST699 only has ONE timer.

This was why, in an earlier post, I suggested that you should consider a
programmable thermostat. This is a replacement room stat which switches on
and off with rise and fall of temperature but ONLY within the times
programmed into it. [Have a look at the CM31 or CM37 in the Honeywell
catalogue which you referenced in your message].

You can thus set the clock on the ST699 to switch on and off at the times
when you want hot water. You can set its heating control to continuous -
which means that the heating will be on whenever (but only WHEN) the room
stat says it should be. If this is a programmable stat, you can thus use it
to control both the temperature AND the timing of the heating. As I said
before, you will then be able to have heating *without* hot water - if that
is what you want.

HTH,
Roger