Thermostat Wiring! Help!

[ltarrant]

Hi,
I am looking for some advice (surprise surprise) on fitting a new heating/hot water programmer.

My current programmer (Danfoss FP715Si) has been playing up for a while so I decided to replace with Honeywell Y9420H Sundial RF² Pack 2. The pack includes new Programmer as well as Wireless Room Thermostat which connects directly to the programmer.

I did some checking on online instructions and it appears the new Honeywell Programmer is wired exactly the same as the old Danfoss. So programmer wise I can clip new one straight onto the old back plate (if I've worked it our correctly?).

My issue is that the current system already has a wired thermostat. However, I decided to get a new Programmer with wireless Thermostat as the current wired thermostat is poorly positioned right by the front door so doesn’t work well.

The part I’m confused on is how to disconnect the existing wired thermostat.

You can see the Installer Instructions here - http://www.honeywelluk.com/Documents/Installation-Guide/pdf/Sundial RF² Pack 2 - Installer Guide.pdf

Section 1.7 mentions removal of existing wired thermostat. It then says about making some minor changes at the 10-way junction box. However, I am unsure whether I have a S, Y, C or W plan and the junction box next to the tank is just a basic 8 way connection block not 10.

Having taken the cover off the existing wired thermostat it seems to just have a Live (Red), Neutral (Blue) & CH On (Yellow) connection. However, when I look at the junction box there are a few red, blue & yellow wires.

Can anyone advise how I should proceed?

Pictures below if helpful.

Thanks,

Luke

View media item 68603 View media item 68604

 

[jackthom]

Can you confirm that the brown/white wire in connector #7 is coming from the black flex leading to the Danfoss valve.

If so, this is almost certainly the wire that is connected to the switched live (yellow) from your thermostat.

If you can identify the flex carrying this yellow you will easily find where the associated red wire to the thermostat has been also connected to the strip.

Remove these yellow and red wires and connect a link between the 2 positions so it's really acting as if the old thermostat were permanently switched ON.

Hope that's not too confusing.

 

[MANDATE]

From photo 1 you appear to have a 3 port mid position valve, which water enters at the bottom port from the pump and the out lets are top left and top right. This would be a 'Y' plan.
Also a 3 port mid position valve would have five wires. earth (yellow/green) neutral (blue) power from room stat to drive valve over first half (white)
power to drive valve over second half (grey) power coming out of valve to light boiler when CH only (orange).
The existing room stat would be wired as follows
wire from programmer CH ON terminal to terminal block (normally T4)
wire from T4 to room stat (red)
wire from room stat (yellow) to terminal block (normally T5) which also holds the 'white' wire.
Of course any of the terminals could be used but T4 and T5 for room stat.
Also even if you had the 10 terminal block, only 8 of the terminals are used
So to simplfy things you have a wire that goes from programmers CH ON terminal to the white wire of valve, it goes via the room stat (which is just a switch) and two terminals in the 10 terminal block or 8 in your case.

 

[MANDATE]

looking at photo I dont think T4 and T5 relate to room stat. cant make out which terminal white wire is in. You may have to trace room stat wires
Looks more like T8 red from programmer and red to room stat and T7 yellow form room stat and white to vale

 

[MANDATE]

Forgot to mention the room stat blue wire.
Again you will need to trace which of the blue wires comes from room stat and remove it.

 

[ltarrant]

Thanks jackthom.

Basically as long as I can find which connector the Switched Live (Yellow) from the thermostat connects to in the junction box, I can then identify the associated Live (Red) and create a permanent link between the connectors at the junction box bypassing the thermostat and creating a permanent switched ON position.

I assume I just then disconnect the remaining Neutral (Blue) from the Junction box. The thermostat is then completely disconnected.

Is that correct?

At work now so can't check connector #7 and flex from Danfoss Valve but will when I get home. Also now slightly confused as comment just in from MANDATE suggests:

"wire from room stat (yellow) to terminal block (normally T5) which also holds the 'white' wire. "

I guess the best thing would be to test the wire but I don't have the equipment for that so was hoping someone would be able to tell my how to figure it out.[/i]

 

[ltarrant]

Oh good. Looks like you both now agree it is most likely connector 7.

So if I pull the yellow wire from connector 7 and establish which red & blue wire come from the same flex. I just need to link connector 7 with the red terminal and remove the blue wire.

 

[jackthom]

Yes I think you've got the idea. In fact you could just connect the red and yellow permanently together at the old room thermostat location but that would turn it all into a bit of a bodge.

 

[ltarrant]

Oh good. Looks like you both now agree it is most likely connector 7.

So if I pull the yellow wire from connector 7 and establish which red & blue wire come from the same flex. I just need to link connector 7 with the red terminal and remove the blue wire.

IF WE ARE WRONG ABOUT CONNECTOR 7 COULD I CAUSE ANY DAMAGE OR WILL THING JUST NOT WORK AND I CAN PUT IT BACK?

 

[jackthom]

Oh good. Looks like you both now agree it is most likely connector 7.

So if I pull the yellow wire from connector 7 and establish which red & blue wire come from the same flex. I just need to link connector 7 with the red terminal and remove the blue wire.

Just to clarify....with everything isolated from the mains...Preferably remove all three wires from the strip and pull the old thermostat flex safely out of the box making sure it's not somehow still live.

Then connect together with a link the strip positions where the yellow and red were previously connected.

Making that one link is very unlikely to cause any damage. You could keep plenty of photos/notes in case the old thermostat needs to be reconnected.

 

[Terrywookfit]

Would it not be easier to use a multimeter, rather than pull wiresand guess?

 

[ltarrant]

Would it not be easier to use a multimeter, rather than pull wiresand guess?

I agree but I don't have a multimeter and for this one of job I was hoping there was a way to determine this looking at the wiring rather than buy one.

As two advisors seem to agree its most likely T7 and any damage is unlikely I will give it a try.

If it fails I'll put it all back and invest in a multimeter. If damage was likely I'd have bought a multimeter.

 

[jackthom]

Just to add that a multimeter would be extremely useful, many would say essential, for this sort of work.

Apart from it's use as a safety check before you put your fingers anywhere inside that box, you could also verify the thermostat switched-live by connecting the meter across #7 and one of the neutral wires while having someone turn the thermostat ON & OFF and hopefully watch the voltage change.

The other strip position you will be linking from is 'CH ON' (from the programmer) which you could also identify the same way while turning the programmer CH OFF/ON.

 

[MANDATE]

On the safety side it is essential the mains power is off, if not then turning CH off and Turning HW off removes power from some of the terminals but not all.
The HW switch on programmers is 'two way' meaning there are two output terminals. there is HW ON terminal and there is HW OFF terminal.
So when HW ON is turned off and no longer 'live' HW OFF is switched on and will be 'live'. (feeding the 'grey' wire of the valve)
Also noted in the instructions page 4, it mentions adding a link from T4 to T5 on the 'Y' plan and it shows a link on the 'Y' plan diagram.
Has you know in your set up these terminals are incorrect.

 

[ltarrant]

Thanks for the help guys.

I managed to borrow a multimeter off a friend so have confirmed the Yellow wire on T7 definitely the Switched Live comes from the Room Stat. One of the Red Wires on T8 is also from the Room Stat and 1 of the Blue wires on T6 is the Neutral.

So I can remove the Thermostat wiring from the Junction.

I just want to confirm I then simply need to make a link from T7 to T8. Correct?

I have made this little diagram of the existing wiring as I know it.

View media item 68634