Bridging-out / disconnecting old wired thermostat

[weezak]

Just installed the new Hive 2 smart thermostat and have a question on how to disconnect the old wired Siemens dial-type thermostat. I believe I have an S-plan heating system with a boiler in the garage and cylinder and pump etc in a cupboard upstairs.

Right now the heating only comes on when the old thermostat is higher than room temperature when the Hive calls for heating. There is a brown (L1) and grey (Y1) wired to the Siemens thermostat in the hall. With the thermostat 'off' there's 240v between L1 and Y1 and when it's 'on' this drops to zero.

This sounds like I should just be able to disconnect both terminals and isolate them seperately so there's never any voltage over these, and the Hive would control the heating as expected. Is this correct, or is there another way to do this? I'd prefer not to do this at the controller side as the wiring in the back box is very tight and obviously I can't see where the wires go if anything were to come loose.

I can supply pics if required.
Thanks for your help.

 

[TCCHeating]

This sounds like I should just be able to disconnect both terminals and isolate them seperately so there's never any voltage over these, and the Hive would control the heating as expected. Is this correct

No. Do the opposite of what you say. If the hive only turns on the heating when the thermostat is turned up, it means you still have the thermostat wired in series between the hive and the motorised valve.

You need to link L and Y1 together. But you should really do this in the wiring center. Not at the thermostat.

 

[Hutchi15]

Hi there,

I have recently installed hive 2 active heating and have replaced my old receiver which was a sunvic xls 207. I fired the boiler up and it seemed to be working well. I then turned on the hive wireless thermostat and noticed this was being controlled by the old room thermostat which is a sunvic tlx 9201. I have disconnected the sunvic thermostat but now the boiler does not fire up.

Can anyone help with how to bridge the old thermostat so the hive thermostat controls the heating?

Many thanks.

 

[JMGas]

Sounds like you disconnected the thermostat while it was still wired in series to the heating, disconnecting it would just make a break in the wiring hence why it's now not working.

If you're heating was working fine before you disconnected the old stat, link out the Live and the Calling (put them back together) and terminate into a chocky block / wrap in insulation tape. This would then let the Hive control the temperature. This however would mean you have Live 240v wires in the wall which isn't best practise.

 

[Hutchi15]

Hi,

I've tried this and it fired straight up. I also had to leave the neutral connected at the recieved and choc block the other end.

I know this isn't best practice but without knowing which cables which at the control box near the tank, there isn't much else I can do.

Thanks again for the advice.

 

[JMGas]

Depends if you have a 3 port valve - Y plan or zones valves - S plan.


If Y plan

You need to connect the White wire (central heating on) from the motorised head to your CH ON wire at the receiver / old prgrammer. And remove existing wires.
This isn't as easy as it sounds, you might have to do some wire finding. This takes the old thermostat out the equation and them wires you linked out are now redundant.

S plan. Find your central heating zone valve. You will need to attach the Brown wire to programmers CH ON wire. And remove the other now redundent wires.

Bit more complicated but sometimes we have to do what you've done.

 

[gsf600y]

Hi,
Resurrecting an old thread, as I've got the same problem.

Basically, I want to know how to correctly remove the old wired thermostat.

Here's the wiring behind the thermostat:

Danfoss Thermostat wiring

• gsf600y
• 1 Jun 2017

There's 2 wires used, and the blue and earth as just dangling there.

In the airing cupboard with the tank, is the following, which I believe is a 3-way valve:

3 way valve

• gsf600y
• 1 Jun 2017

3 way valve 2

• gsf600y
• 1 Jun 2017

And also in the airing cupboard, the black cable from the valve connects into this box:

wiring center.

• gsf600y
• 1 Jun 2017

(messy wiring underneath I know - it's not clamped within the box hence is just falling out)

Within that controller box is:

Heating wiring control box

• gsf600y
• 1 Jun 2017

So, am I correct in thinking these are the options I have:
option 1 - simply connect the 2 thermostat wires together, push it all back into the wall, and mount the new Hive wireless thermostat over the top.
This means I've got live cables in the wall still.

option 2 - somehow "disconnect" the thermostat completely, leaving the cables in the wall, but they would just be dead cables. I can then plaster over the old thermostat hole completely.


Option 1 - I can do, easy enough, but wont be as aesthetically pleasing, and has the risk of live cables in the wall.
Option 2 - sounds preferable, but I don't know how to do it

From the above post:
"You need to connect the White wire (central heating on) from the motorised head to your CH ON wire at the receiver / old prgrammer."

So, the white wire in the control box is joined up to another wire in the choc-box, and that then goes all the way down to the boiler control?
And I'd need to figure out which wire this is at the boiler controller end somehow (??), and wire it up to "CH ON"?
And the cable already in "CH ON" is currently wired up to the old thermostat, and that can just be disconnected?

Hope someone can help!

 

[gsf600y]

Heating system wiring diagram

• gsf600y
• 3 Jun 2017

I've created a diagram of the wiring in the airing cupboard.

Can anyone help me work out how to correctly disable the wall thermostat?

Should I just disconnect all it's cables in the choc-block, and the move the white cable into the 8th choc-bloc position???

 

[Shakinsteve]

Heating system wiring diagram

• gsf600y
• 3 Jun 2017

I've created a diagram of the wiring in the airing cupboard.

Can anyone help me work out how to correctly disable the wall thermostat?

Should I just disconnect all it's cables in the choc-block, and the move the white cable into the 8th choc-bloc position???

Did you ever resolve this as I am in the same situation?

 

[gsf600y]

No, I didn't - the old thermostat is still on the wall
I removed the thermostat off the wall, connected the yellow and red wires together temporarily, and then tested various red and yellow wires in the junction box for a circuit - no joy. At that point, I gave up.

I recommend you try the same though. Do you have a multimeter?

 

[CupRS]

Hi, I’m just about to do the same setup, heat link side I’m happy with but will have same wiring to do when I remove the old stat.
Did you manage to get the stat successfully disconnect?
Cheers

 

[stem]

The old thermostat can't simply be disconnected as this would leave the heating wiring 'open circuit' and it would not operate, the integrity of the circuit needs to be maintained. As not all thermostats are the same, or indeed wired the same, the specific instructions given to one poster may not apply to another. So, whilst the steps are the same, some working out will be required in each case.

1. Look at the wiring diagram for your make/mode of thermostat that you are removing. If you don't have the instructions for it, a diagram is usually printed inside the lid. This will show which are the two switching wires, and which is the neutral wire. (If there is a neutral present. Not all thermostats need or have one fitted)

2. Trace the thermostat cable back to its origin.

3. Take take a photo, or make a note of where the switching wires are connected at their origin.

4. Disconnect all of the wires going to the old thermostat and remove the cable and thermostat. All other wires to remain in place.

5. Insert a wire link between the terminals where the two switching wires have just been removed from, so that they are now electrically joined together.

 

[gsf600y]

yeah, it's step 2 I'm failing on.
I thought the thermostat's wires went into the junction box in the airing cupboard, but having tested all those for a circuit, I'm now thinking that they must go to the controller under the boiler in the kitchen.
I'll have to get the multimeter out again this weekend.

 

[stem]

This often happens unfortunately. That's why step two is.

2. Trace the thermostat cable back to its origin.

..or, in other words don't guess where it goes.

There is no fixed way to wire up these systems. As you rightly say, the thermostat may be wired back to the wiring centre, or the programmer. Both are correct. It all comes down to the layout of the property, any existing wiring being reused, and the personal preferences of the installer.

Occasionally you find an installation (usually an S-Plan) where the room thermostat has two separate cables going to it. One 'in' from the programmer and another 'out' directly to the motorised valve. Taking that out of circuit generally means running a completely new cable, between the Hive and the motorised valve. Fortunately there aren't that so many like that about, but I've come across one or two.

 

[CupRS]

Thanks for your help Stem, everything seems to be working..
Cheers