Update: Adding a wireless room thermostat (help needed)

[JH]

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

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

Jules

PS - I've left the CH wired back into the existing timer to get heating and water to work.

[Mike Hibbert]

Hi Jules,

I'm not gonna be any use here, but, I have just posted wiring question about the CM67 RF, seeing that you managed to wire it in successfully, any advice you can give me will be great!

Cheers Mike

[JH]

(putting to one side the problem I currently have)

I was unsure to start with too but studying the wiring diagram (diag 5 c on the install instructions) and help from this newsgroup helped (see my original query)

reality, it is really straightforward. In simple steps,

1. wire in a main supply (L+N)
2. link with a wire the live terminal to the 'A' terminal
3. wire the brown control wire (labelled BR in diag 5c) from the zone value to the 'B' terminal

and that's it.

Jules

[Mike Hibbert]

> In reality, it is really straightforward. In simple steps,

Thanks Jules,

So the live is a "real" live and the terminal "b" is your switched live back from the stat?

Cheers

Mike

[Ed Sirett]

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.

[JH]

Thanks Ed for the reply - I've lurked many years on this group an respect your comments and like you I cannot understand the behaviour. The system in "old" mode does work independently. I'll take another look in the morning - the only idea I have is that I didn't wait long enough testing the new set up for the H/W to kick in, but that's _really_ clutching at straws.

Jules

[JH]

frame=right&th=ec6714d44df72819&seekm=2EiJb.15422%24FN.2759%40newsfep4-winn.> server.ntli.net#link1

Yes, 'B' is the switch the stat uses to turn the system on and off to maintain the room temperature.

Why on earth the manufactures make it out to be rocket science is strange - all central heating does is turn on when the time is right and the temp is too low.

Caveat - my new set up is still not working properly so maybe it is rocket science.

Jules

[Ed Sirett]

Well up to about a 30 seconds or so. Um... HWC was not already heated ?!?!?

[JH]

I checked the wiring again and the problem is solved - it's so obvious and rather embarrassing.

Basically, the original test to determine which two pins controlled the CH and HW was cocked up.

I originally thought pin 3/brown controlled the CH and pin 6/blue did the HW - wrong its the other way round!

With pin 6/blue wired into the room stat and pin 3 left alone this time everything is working properly. The annoying part is that I used brown wire to extend the ON wire to the new stat so it now looks a bit of a bodge as a blue wire is connected to a brown one.

So Mike, the wiring is straightforward, just avoid the mistake I made!

Thank you to everyone who helped.

Jules

[Mike Hibbert]

With your advice, (and thanks to Lurch's help!) I have just done it, and blow me, it works!

Cheers

Mike