Replace CM61NG+HC60NG with Nest + weird boiler problem?

[leeovery]

Hi

Firstly Im looking to replace the CM61NG Wireless programmable Thermostat + the receiver HC60NG with the Nest thermostat.

Ive looked at the wires and seems a pretty simple swap but just looking for confirmation from somebody please.

The wires are labelled N,L,L A,B,C,D,E on the old receiver.

Obviously the first N&L are neutral and permanent live which swap directly to the Nest Heat Link.

Currently I have a brown wire coming into the A terminal and a black wire coming into the B terminal. Nothing coming into any of the others.

Which of these is the call-for-heat and which is the common?

Another problem Ive got is that my Vaillant ecoTEC boiler display is OFF when the boiler is OFF. The display only lights up when the boiler is called upon to supply heat for the water or the various heating zones.

After looking at the wiring diagrams for the CM61NG receiver, am I right in thinking that the C terminal should have a permanent live bridged from the L terminal?

Can anybody confirm this is the case and if so, how would I make this work when moving across to the Nest system?

Ive attached a few pictures of the setup I have currently. Its 3-zoned, with upstairs and downstairs heating, and then towel rails and obv hot water. Im wanting to only replace the downstairs heating with the Nest system which is currently controlled using the CM61NG+HC60NG, along with the zone valve in the image.

I would REALLY appreciate any guidance here!

IMAGES: https://www.dropbox.com/sh/f5tj2w4q9jp24et/AACKWzTVzgAbZdvlGV0zWR6ta?dl=0

Thanks.
Lee

EDITED: I edited to correct terminal letters as I had labelled them incorrectly in the post.

 

[Dan Robinson]

Sounds like you have screwed up the permanent live to the boiler.

 

[leeovery]

Sounds like you have screwed up the permanent live to the boiler.

Thanks for the reply.

I havent screwed anything up - yet!

I havent touched anything, just looking at this stage. Had the problem since we moved in but have just realised [potentially] how to fix it having studied the wiring diagrams due to wanting to install the Nest system.

Just looking for some help / guidance / advice.

 

[MeldrewsMate]

Lee, the wires from A and B are connected together when the downstairs stat calls for heat, In all probability one (A or B) is connected to the downstairs timer output, and the other to the brown wire of the downstairs zone valve.

Agree with Dan, it looks like the zone valve outputs (orange) are commoned up and used to power the boiler. That's not right and needs to be corrected or you may find the expensive pcb goes pop sooner than expected.

Once the permanent live is connected to the boiler it's a case of removing the L to SL link and feeding the ZV outputs to the SL of the boiler.

 

[leeovery]

Thanks for the reply. Didnt follow most of it but will reread later and try to understand (I'm just a DIYer - guess that was already obvious )

At present I don't have anything coming into the A terminal, only N, L, B & C.

Once I determine what b & c are for I can install Nest and also begin to understand what's going on with the boiler issue.

 

[Dan Robinson]

A is common.

B is call

C is satisfied /call for cooling.

If there is nothing on A, then your system won't work.

 

[leeovery]

My apologies!

I misread the terminals. I read the blank one (4th from left) as A.

Ok so A and B are wired currently. C is blank.

Am I right in thinking I can just take A & B and switch across to the Nest Heat link?

Additionally, should the C terminal have anything in? Looking at the wiring diagrams it looks like it passes the live down to the boiler when the valves are shut.

???

 

[leeovery]

Quick question, if its not too much trouble:

Lee, the wires from A and B are connected together when the downstairs stat calls for heat, In all probability one (A or B) is connected to the downstairs timer output, and the other to the brown wire of the downstairs zone valve.

What do you mean by downstairs timer? The device I'm talking about is the wired receiver for the wireless downstairs thermostat / programmer. Bit confused.

Am I right in thinking that the orange output from the zone valve supplies the live to the boiler?

I will go ahead and install the Nest system as thats a straight swap. Would love some more guidance on fixing this boiler issue. I don't intend on fixing it myself but would help to understand more whats going on so I can explain to a pro.

I appreciate the help you guys have given already but struggling to completely understand, sorry!

 

[jackthom]

My apologies!

I misread the terminals. I read the blank one (4th from left) as A.

Ok so A and B are wired currently. C is blank.

Am I right in thinking I can just take A & B and switch across to the Nest Heat link?

Additionally, should the C terminal have anything in? Looking at the wiring diagrams it looks like it passes the live down to the boiler when the valves are shut.

???

Yes just transfer the existing Live, Neutral, A and B across to the heatlink.

I can't see any reason to use the C terminal (satisfied) unless you have a cooling system. Which diagram shows it connected to the boiler?

The boiler and heatlink etc should have a permanent Live if they don't already. The orange switched live from the zone valves needs to go to the Switched Live terminal on the boiler PCB.

 

[leeovery]

I can't see any reason to use the C terminal (satisfied) unless you have a cooling system. Which diagram shows it connected to the boiler?

I misread this. Ignore that!

Thanks for your help. Happy to proceed with the Nest install.

Now just need to understand and fix the boiler issue...

 

[jackthom]

Now just need to understand and fix the boiler issue...

Can you confirm that your boiler and receiver do not have a permanent mains connection but are powered only when the zone valves are activated?

 

[leeovery]

Now just need to understand and fix the boiler issue...

Can you confirm that your boiler and receiver do not have a permanent mains connection but are powered only when the zone valves are activated?

The boiler display only 'lights' up when the boiler is running. I realised this a while back when I had pressure problems. Couldn't check the digital pressure gauge without the boiler running. Whack the heat up and the boiler kicks in and then the display is activated. Heating goes off = so does the boiler display.

The thermostat / receiver work fine. Not sure what you mean by 'receiver'? Do you mean the Honeywell receiver which works in combination with the wireless thermostat/programmer?

 

[jackthom]

Sorry if I'm confusing things, so basically it's just the boiler that is switched on and off by the zone valves.

The boiler should have a permanent mains Live and remain on whenever the rest of the system is powered. The zone valve orange should go to the boiler Switched Live (usually terminal 4 on the PCB but check the particular Vaillant installation manual).

Is there a short wire link between the boiler terminals 3 & 4 at the moment?

 

[leeovery]

Im following you so far

Just popped the cover off the boiler and yes there is a short link between terminals 3 & 4

Photo:
https://www.dropbox.com/s/r9xe6oi2h2l02v3/2014-12-08 12.11.15.jpg?dl=0

What does that mean?

 

[jackthom]

Those 2 terminals are where in a simple syatem you would normally wire a thermostat. When they are connected together, terminal 4 becomes Live and the boiler fires up; so in this case the boiler fires whenever it is powered up.


The brown wire going into the L terminal of the boiler should be permanently Live.

The wire link should be removed and a new wire fed from the zone valve(s) orange is needed to connect to terminal 4, Switched Live.

(Terminal 3 is not required in this case)