Trying to swap center receiver on combo boiler

[Abbie8]

Hi - I have a basic knowledge of electrics but my boiler thermostat has flummoxed me

My boiler is an ideal logic+ combi boiler that already has a center thermostat fitted - the receiver next to the boiler and a separate wireless thermostat controller.
I have dropped the controller and it is broken, so am looking to replace and thought about upgrading to the Tado thermostat.

When I look at the center receiver wiring - I have a N, L and earth terminal which seem self explanatory - I assume this is my electrical connection to make it work.

I then have two other terminals connected - one marked A and one marked B. I think this is the boiler switch connection or certainly the connection to the boiler.

I also have a loop wire from the L terminal to the A terminal.

When I look at diagrams of the Tado receiver wiring, there are no terminals marked A or B. I have not bought the Tado system yet, as I want to make sure it is compatible to the wiring that I already have.

I have found one diagram online that looks like the A wire should be connected to the terminal CH NO and the B wire should be connected to the CH COM terminal. Is that correct or is it the reverse??

For the loop wire connected to the L terminal that currently goes to A - Where should that go to? The CH COM??

Any help appreciated and sorry if this is obvious!

 

[CBW]

Yep, so L and N are for the power source, the link is often needed for the switch to work, however unsure why you’d need it if you have both a and b wires.

If you wanted Tado, then yes it would be A to Com with link (otherwise might not work) and B to NO with the L, N and E connected to their respective terminals.

 

[Abbie8]

Thanks CBW - very helpful!

 

[Madrab]

the link is often needed for the switch to work

Not wishing to contradict another pro but the link (L>A) is just to provide a 240v switched live out through B from the receiver, the link (A) doesn't power the internal switching the receiver power does that. The internal A>B switch is just a volt free switch. As the Ideal uses a switched live - the Live link (L>A) in the receiver allows the 240V to be sent to the boiler. When the stat called for heat to the receiver, the receiver switches A>B internally, that sends the linked Live 240V > A to the boiler via B and turns it on.

Presume you are looking at the wireless TADO? If so then you would do exactly the same, connect L&N for the receiver power then link the Live (L) to the COM (A) and then the NO (B wire) out to the boiler.

(edit added thumbnail)

 

[RandomGrinch]

If so then you would do exactly the same, connect L&N for the receiver power then link the Live (L) to the COM (A) and then the NO (B wire) out to the boiler.

Not to contradict the contradictor

There are wires connected to A and to B of the existing thermostat AND a link wire between L and A.

In this case, I would connect the existing wires to COM and NO; the link wire may be completely superfluous and I would leave it out (and the possibility for it to cause further confusion!).
It also saves having to safely park the extra wire (that's currently connected to A).

I would only add the link back, if the system didn't work.
Perhaps a task for the OP to experiment with now (with power safely isolated of course!)?

 

[Madrab]

Not to contradict the contradictor

There are wires connected to A and to B of the existing thermostat AND a link wire between L and A.

Indeed, there may be the live on A and B is the switched live, just presumed given there was a link in there that A wouldn't be live but on reflection then A wouldn't need to be there if it wasn't. It even shows that in the wiring diagram ... DOH

All that being said though, could always get the wireless + extension kit or the hard wired version and just use OT. Though I have seen that OT and the Logic +'s can be a bit flaky.

 

[Abbie8]

Thanks all - I am going to buy the wireless + extension and I will follow your guidance. To start with I will connect all existing wires as you suggest (using existing A & B and the loop) and go from there .

I will let you know! Thanks again all.

 

[Madrab]

Don't use the loop, as suggested. Try without the loop first. Please do test everything though, get the circuit tester out and check if A's carrying the Live first.

 

[ianmcd]

The loop is not required