replacing room thermostat - wiring question Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[ccrobins]

I am trying to replace my mechanical thermostat with a programmable one to enable me to time when the boiler goes on and off etc.

I am replacing a Robus RRF10 thermostat with the wiring as follows
1 none
2 Live (brown)
3 Neutral (grey)
4 none
5 Live linked across to 2
6 Black wire (not sure what it is)

I am trying to replace with a Danfoss TP5000M Si and to begin the wiring looked simple to replace however now it makes no sense to me as a novice. page 4 at http://danfoss-randall.co.uk/PCMPDF/082.pdf shows how it should be wired, using what i have above i used the brown and grey as live and neutral into the relevent L and N to the right with no remote input. what i put on the other side to NC COM and NO i think is where i am going wrong - i have tried live to the NC and the black wire to NO but still nothing is working - can anyone advise correct wiring ??

would it only work if an earth is connected ?

any help great ly appreciated

[stoneyboy]

ccrobins,
Assuming you have the 240v version you will need to put a link from the L terminal to the COM terminal and connect the black wire to the NO terminal. Since the instructions do not specify whether NO or NC is active with a fall in temperature you may have to swap the black lead onto the NC terminal (if the heating goes off when the temp is too low). Don't forget you will need to have the controller switched to continuous.
end

[plumbbob]

The wires in the Rf 10 are:

Pin 2 live
Pin 3 switched live to boiler
Pin 5 link live to neon
Pin 6 neutral connection from neon


It's a little unclear from the datasheet what pin connections the new stat has. What are they? If you follow Stoneyboy's advice it will go bang as the black wire is a neutral.

[ccrobins]

thanks for the advice and yes its the 240v version. not sure i want it to go bang however !

new danfoss controller has the following
A - labelled as N for neutrak
B- labelled as L for live
C - earth
D&E are for remote sensor so i am ignoring those

then i have
1 - N/C
2 - COM diagram indicates it to be a switch
3- N/O

and thats everything - sorry not to explain it better but to be honest i really dont understand whats what

[plumbbob]

The wiring should be

A - connect black wire
B - connect brown

2 - link to connection B

Now the trick thing is where does the grey wire (which is not a neutral) go? I would normally connect it to pin 1, the NC so when the temperature reaches the limit the contacts will open switching off the heat but the instructions say use pin 3 - NO????

Connect the grey to pin 1 and if the heat comes on when you turn the stat down, swap it to pin 3.

Another point, if you have a timer fitted, it needs setting to 24hrs otherwise the programmable stat may lose its settings as it should really have a permanent power supply.

Just a point as you have tried several combinations of wiring ensure no fuses have blown and the supply is live.

[ccrobins]

plumbbob - i am a little confused when you say that the grey wire that i have is a switched live to the boiler as the diagram on the back of the rrf10 shows this to be neutral into pin 3

wish i had never started this now - i made the assumption that it was simple to change the thermostat, now facing the prospect of potentially making a bang and ruining the thermostat - maybe best just to swallow pride and get someone in

[stoneyboy]

ccrobins,
Looks like you had better get a specialist in.
You have told us that you have 2-live, 3-neutral, on the existing controller.
Taking plumbbob's pin listing for 3 as being switched live (not neutral) the existing controller should have already gone bang.
Please get someone in to identify the existing wiring.
end

[stoneyboy]

ccrobins,
Sorry, your identification of the grey wire on terminal 3 of your existing controller as being neutral threw me.
Following plumbbob's warning your existing wiring is 1 unused, 2 live -brown, 3 switched live - grey, 4 unused, 5 neon (with link to 3), 6 neutral - black.
The new thermostat should be wired A neutral - black, B live - brown, link from B to 2 (COM), 1 NC - grey. Again you may need to swap grey onto 3 NO if the thermostat works the wrong way round.
Thanks to plumbbob for the warning.
end

[plumbbob]

No, Crobbins, the instructions say

"For the neon indicator, a neutral line is required. Connect N to terminal 6 and link terminal 5 to either terminal 4 or 3" .

So the neutral is pin 6 which is the black wire!

Instructions also say, "For heating control use the normally closed contact (terminals 2 and 3) ".

So the live (brown)is as you said is pin 2 and the switched live to the boiler (grey) is pin 3.

[ccrobins]

Brilliant many thanks stoneyboy - I'll giove it a try tonight when i get home and hopefully I'll have some good news to report !

serves me right for assuming i could just change it over simply - give me copper pipes and solder anyday rather than electrics

[ccrobins]

Well I have done as you suggested stoneyboy and thought I had it cracked, thermostat powered up and I set time/date and programmes and left it to it and all seemed well but then it started clicking like it was switching on and off. On closer inspection it seems to do this when it reaches temperature and should be telling the boiler to stop. As stoneyboy suggested if the thermostat works the wrong way I tried it with the switch live (grey) into NO instead of NC however the thermostat did not power up when I did this


Sorry but I’m stumped again !

[stoneyboy]

ccrobins,
I would have expected the programmer to work with the grey wire fitted onto the NO terminal. If it worked with the grey wire onto NC changing it onto NO should not stop the programmer powering up. Check that the L and N connections are OK and that the wires are not broken.
I assume you did fit a wire link from LIVE to COM.
Have a look at the web page you gave a link to in your first post, are all the dip switches set as shown on page 2? Correct them if necessary and push the reset button this will reset the programmer to its factory set status.
end

[ccrobins]

dip switches set ok and yes i put a wire between live and COM. I was wondering what would happen if i put the switched live to COM and the LIVE link wire to NC ?

thanks for all your help on this

[ccrobins]

tried all that but unfortunately no change ?

what would happen if i changed over the switch live in NC with the Live in COM ? just wondering if this would make a difference as now clutching at straws !

thanks again though you have helped me get much further than before

[stoneyboy]

ccrobins,
The wires going to NC NO and Com should have no effect on the controller - it should power up with nothing on these terminals. Try the controller with just L N and E (if there is a terminal for E) connected it should display its settings. If it does not then you do need to check it is getting power - has the main controller turned heating off? Has the fuse blown?
If it does not work with only L and N connected (to L and N terminals) you will have to return it as a faulty unit.
end