Replacing Drayton Digistat SCR + LP522 with Tado

[UnusualCapybara]

Hi,

Moved into a new house which has a Worcester GreenStar Danesmoor 25/32 oil boiler which is controlled by a Drayton LP522 timer panel with separate controls for hot water and heating. A Drayton Digistat SCR is paired with an RF601 room thermostat.

My plan is to leave the LP522 to control the hot water as that's a pretty static task, but remove the Digistat SCR and RF601, replacing them with my Tado receiver for heating control.

I have pulled the cover on the Digitstat SCR to see the wiring (photo attached). Can someone help me understand how to connect that same wiring to the Tado receiver (photo also attached) please?

 

[ericmark]

Likely on the back of the room thermostat it will have a wiring diagram, where you can confirm that brown is live, blue is neutral, and black and grey and com and N/O but you need to confirm this by looking on the diagram on the back of the thermostat.

Also confirm before you start all is working as it should, often oil boilers work on C Plan and DHW can't be turned off, but before you start make sure all is working, as if not after you don't know if something you have done or not.

 

[UnusualCapybara]

Thanks for the quick reply. I have checked the back of the existing receiver and it confirms:

N - Neutral
L - Live
1 - Common
2 - SAT (?)
3 - Call

In this case am I right in saying I could set the heating to be permanantly 'On' on the LP522 timer, then:

- connect the black from '1' on the existing controller to 'CH COM' on the new Tado receiver
- connect the grey from '3' on the existing controller to 'CH NO' on the new Tado receiver?

The desired behaviour is that the Tado receiver governs the call for heat.

Thanks again

 

[RandomGrinch]

...and for whoever wired up that stat, it's a good thing that it's volt-free switching, otherwise the results may have been interesting!

In this case am I right in saying I could set the heating to be permanantly 'On' on the LP522 timer.

Yes.

- connect the black from '1' on the existing controller to 'CH COM' on the new Tado receiver
- connect the grey from '3' on the existing controller to 'CH NO' on the new Tado receiver?

And yes

Don't forget the earth connection as well.

 

[UnusualCapybara]

Oh wow I just noticed that! Presumably they've made the same mistake at the other end of that cable (i.e. brown where blue should be and vice versa)? Or is it possible that they've crossed them over at one end only but it's still working?!

 

[RandomGrinch]

Or is it possible that they've crossed them over at one end only but it's still working?!

It's probably just this end. But its worth checking the other end of the cable. It would work regardless.
Some thermostats internally link the common to the live, rather than having a separate terminal. In that case, the installer would have quickly noticed their mistake!

 

[ericmark]

Well spotted @RandomGrinch normally I find the thermostat on the internet, but it seemed pointless when the instructions will be on the back.

I have considered changing my own thermostat, but mothers house had so many problems with wireless link, so not keen on wireless, at the moment using Nest Gen 3, as it sends info through the same two wires as it gets the 12 volt power, so all done with two wires boiler area to main house. But Nest Gen 3 does not connect to TRV heads, it said it did, but alas that's not true, but mainly the problem is house design, late mothers house worked fine without linking TRV's, but this house hall cools too slow.

Looked at Tado but info was not readily available, it seems some models not for sale in UK, same with Nest USA Nest has temperature senders but not the UK model.

And all central heating should come from the same 230 volt supply, otherwise and UPS system to keep it running will not work. However my TRV's with this house (oil fired) have not worked anywhere near as good as with late mothers house (modulating gas) how much down to how pipework installed and how much down to on/off boiler I don't know.

So a report back on Tado would be nice, does it really allow individual room control? My nine programmable TRV heads should allow individual room control, but getting the boiler to fire when required is a problem, so please report back on how it goes.

 

[UnusualCapybara]

Will report back on Tado. It worked really well in our previous house with a combi boiler but the jury is out on how well it will do here. I can see two potential failings:

1. You can only have a single internet bridge and can't add extenders etc so distance between the bridge and the valves can be fragile. This new house is 4,000 sqft so I can see that being a fall at the first fence.
2. There's miles of pipework and I wonder how quickly the system will be able to fire the boiler and react to individual room calls for heat.

Watch this space in a day or two!

 

[UnusualCapybara]

Bit of an update on Tado, not a positive one unfortunately.

Firstly, installation of the control unit was easy thanks to the advice given on this thread and all looked good to start with until I realised that some of the valves further from the bridge were randomly disconnecting or worse still claiming to be calling for heat but nothing happening.

Tried moving the bridge around the house but that just shifted the problem to different valves so have unfortunately concluded that the house is just too big for Tado's single bridge approach which is a shame because I really like the product.

Now researching an alternative smart thermostat system with Matter support which can also call for heat!