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
Here's the old wiring into the existing timer from left to right
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
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
PS - I've left the CH wired back into the existing timer to get heating and
water to work.