28CDi RSF Worcester Bosch Tado Thermostat

dawwad50 · 9 Dec 2019

Hello,

I currently have a Worcester Boshch 28CDi RSF Combi Boiler and would like to connect this to my new Tado Smart Meter.

https://www.worcester-bosch.co.uk/support/literature/download/8716145020

Reading the manual, it seems that ST8 (figure 11) is the terminal to which I should connect the thermostat to.

https://www.tado.com/start/manuals/st/102022_E-ST01IB01-INSTALLER_MANUAL_RELAY-TA-UK-03.pdf

Off the boiler, where does Ns Ls and Lr connect to on the Tado terminals?

Can you please let me know which terminals to connect?

Thanks in advance.

Wadoud

stem · 9 Dec 2019

If it's just the Smart Thermostat you are installing as below, [ie not the extension kit]

Then you just need two wires connecting, the Tado Smart Thermostat doesn't need a neutral connection.

Ls (Live supply) goes to the Smart Thermostat 'COM'
Lr (Live return) goes to the Smart Thermostat 'NO'

If you have any existing controls they would need to be removed / decommissioned as appropriate.

To get to the wiring terminals of some combi's it's necessary to open up a room sealed compartment. If your boiler is like this it's not a DIY job and should only be done by an RGI (Gas Safe) engineer who can perform the necessary safety checks to make sure that it is sealed up properly again afterwards.

dawwad50 · 9 Dec 2019

Hi Stem,

Thanks a lot for your help. Really appreciate it.

Sounds like its just two wires as you described.

I have previously connected the Neutral and somehow fused out the boiler. I replaced the fuse and will now try what you described tonight.

Boiler terminals are easily accessible so luckily don't need an RGI engineer. Thanks for the advice!

stem · 9 Dec 2019

You may find that you have damaged the boiler or the Tado. The three Tado terminals NO, NC, and COM are all live connections. If you put a neutral in one of them and have blown a fuse, you will have effectively joined the Live and Neutral wires together and created a short circuit

Some are lucky and get away with it, others not so.

The unused neutral wire can be put in one of the 'Parking Terminals' to keep it isolated and out of the way. That's what they are there for. If there's an earth wire present also, that can go in another one.

dawwad50 · 10 Dec 2019

Hi Stem,

I tried to connect the terminals as suggested yesterday, but unfortunately the boiler fused out again.

I replaced the fuse and everything is operating as normal. The Tado still gives regular display so I am not sure this is damaged.

Not sure where I am going wrong with connecting the Tado. Please note that I am taking the loop metal pin out (that already exists to connect LS and LR within the boiler).

Worcester Bosch finally replied via their technical support email:

"ST8 would be the connections for which a third party thermostat would be connected to the boiler.

LS - Provides a permanent 230vac supply to the controller and LR is the switched live demand back to the boiler. As a third party unit TADO would need to provide the correct connections for the unit to provide the 230vac switch back to the boiler"

I am still waiting to hear from Tado.

Any tips?

Thanks!

stem · 10 Dec 2019

stem said:
Ls (Live supply) goes to the Smart Thermostat 'COM'
Lr (Live return) goes to the Smart Thermostat 'NO'

dawwad50 said:
LS - Provides a permanent 230vac supply to the controller and LR is the switched live demand back to the boiler. As a third party unit TADO would need to provide the correct connections for the unit to provide the 230vac switch back to the boiler"

So we both gave the same answer

these are the only connections you need:

The link between Ls and Lr should be removed when the thermostat wires go in. The link is there so that the heating can operate when there isn't a thermostat connected. Inside the Tado when the thermostat switches 'on' the wires in NO and COM are simply electrically connected together by a switch, and effectively form a link between Ls and Lr.

Make sure that any other unused wires are isolated and not touching anything they shouldn't be.

The Tado is battery operated so I would expect the display to be fine, it's not connected to the 230V side. It's the 230V switch inside that can be damaged. What sometimes happens is that the internal switch contacts weld together because of a short circuit, but if that happened the Tado wouldn't be able to turn 'off' the heating, it would be permanently 'on'. It wouldn't however blow a fuse, so that will be something else.

dawwad50 · 10 Dec 2019

Thanks for your help so far Stem, I will make sure that the wires are isolated on both ends. Will have to push it to the weekend as I have run out of 2A fuses.

Checking further on the website, it seems that I am recommended to get an extension kit, although I am not convinced.

https://www.tado.com/gb/products/extension-kit

I am not convinced since there is a thermostat terminal on the boiler. Additionally, I still can't confirm that the Extension kit will also not fuse!

Any thoughts?

stem · 10 Dec 2019

The extension kit is used for heating systems with stored hot water (ie a hot water cylinder) or when you wish to use the Tado thermostat wirelessly. [The extension kit still has to be wired, the thermostat then communicates with the extension kit wirelessly, so can be located remotely without the need to run wires out to it]

As you said you had a combi, and wanted to connect the thermostat to it I assumed that it doesn't have a hot water cylinder attached. If you do have a hot water cylinder attached (rare for a combi) the thermostat doesn't connect to the boiler at all, it connects to a motorised valve.

The fuse is blowing because there is a short circuit somewhere.

dawwad50 · 10 Dec 2019

Thanks Stem.

Indeed, I have a combi without a hot water cylinder. I do not intend to buy the extension kit as I simply wish to turn boiler on/off using the app.

I will continue with the assumption that there is a short circuit, probably with my introduced wiring and then re-start again.

Thanks and will update you this coming weekend.

stem · 10 Dec 2019

You're welcome.

FYI the Tado thermostat works the same whether you wire it to the boiler directly, or use it wirelessly with an extension kit. In operation you wouldn't notice any difference.

dawwad50 · 16 Dec 2019

Hi Stem,

Just to update you that now the connection seems to be successful- no more fuses blowing!

It was the case of loose wires, I simply made the connection more robust.

The next challenge is to ensure the Tado is actually controlling the boiler! Not a wiring issue though.

Thanks!

Wadoud

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28CDi RSF Worcester Bosch Tado Thermostat

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