"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.