On Sat, 17 Jan 2004 16:33:07 +0000, JH wrote:

Hi,



Some readers may remember a couple of weeks ago I asked about adding a
wireless room stat to an existing system (S plan, 7 day timer, independent
hot water and heating)



Based upon the very helpful advice from this group I've now installed the
Honeywell CM67-RF unit (87 quid from rkm-heating-controls BTW). This unit is
a 7 day wireless programmable room stat and means I don't use the existing
timer to control the heating at all but I've left the existing timer to
control the hot water.



I have now wired it all together but there's a problem.



Test 1 - test heating only using the CM67

Power on, go to manual and it's good news. The heating works fine, the
boiler fires, the pump whirs, radiators get hot and the CM67 is happy to
control it. I've still to program the unit but that can wait.



Test 2 - test water only using the existing timer

Power on and the existing timer is working so I set the time and day and
switch the unit to constantly heat the hot water. The hot water light on the
timer comes on but nothing else happens, no boiler, no pump, no valve
action. Oh dear.



Test 3 - wire the heating back to how it was, into the old timer unit, to
make sure something hasn't broken (lose wire etc.) during installation.

Both heating and water work together and independently fine - just like it
use to.



Here's the old wiring into the existing timer from left to right
http://www.jjh1.demon.co.uk/wiring2.jpg



Pin 0 - earth (green and yellow) x2

Pin 1 - neutral (blue)

Pin 2 - live (brown)

Pin 3 - ON (brown)

Pin 4 - C (jumper wire from pin 2)

Pin 5 - OFF (no wire)

Pin 6 - ON (blue)

Pin 7 - C (jumper wire from pin 2)

Pin 8 - OFF (no wire)



I worked out which ON wire controlled the heating by disconnecting each ON
wire in turn. It turns out the brown wire on Pin 3 controls the heating.



For the new wiring I've simpled wired the brown wire on Pin 3 into the new
unit.



Now I'm confused as to why in the new set up the heating works but the water
doesn't. Any ideas?




Thanks in advance


As presented here there is really no reason why the new set up should have
lost the HW.

I think you'll have to see where the blue wire in the right hand flex (the
HW on signal) goes to. I would assume it goes to the HWC stat and then to
the HW zone valve (S-plan or equivalent I presume).

Every idea I have thought of comes up to a contradiction of the reported
behaviour.

The only one which I think holds out any hope is that the CH and HW are
some how reveresed and the timer is in '10' or 'gravity' mode and won't
let you do HW without CH (sic) AND the boiler etc. is fired of the timer
(via the room stat). This however suggest the HW and CH were not be fully
independant beforehand.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html