Greenstar CDi Classis System ERP + Evohome OpenTherm

[zak1981a]

Hi,

I’m new to the forum and would like some advice.

I’ve had Evohome in my home working for 5 years; HR92s on all radiators, Evohome hot water control on an unvented cylinder, and Evohome underfloor heating controller. Boiler is Greenstar 30 CDi Classic System ERP without integral diverter valve and Worcester 216l unvented cylinder. This has been set up on a standard S-Plan plus configuration:





When I first ordered the kit I also bought the R8810A1018 OpenTherm bridge as well as the Nefit Opentherm to EMS converter (7746901847) however the engineer at the time could not get it to work, there was no power to the OpenTherm bridge via the Nefit converter and the engineer lacked experience of Evohome.

It’s always been an itch of mine to scratch and now that I have some time on my hands I want to see if I can get it to work and possibly try/have an engineer try. I know I should not be trying to ‘fix’ something that isn’t broken however I have all the kit (I believe) so the question of if it’s worth it doesn’t come in to it, worst case scenario I am only paying for an engineers time (if necessary).

Based on some research recently I have understood a little more about the problem.

Problem: Without an ‘Integral Diverter Kit’ the boiler disables the BB connectors on ST19.
Solution: Fit Worcester Bosch Code Plug 1002 to enable BB Connectors.

Reference:
https://www.worcester-bosch.co.uk/profe ... ing-issues
https://bbqkees-electronics.nl/2024/06/ ... h-as-well/

I determined it was Code Plug 1002 required based on installation manual for the Integral Diverter Kit (https://www.worcester-bosch.co.uk/profe ... structions)

New Wiring Scematic to get OpenThem working:



Notes on plan:

Zone Valves do not send a 230V live return back to boiler therefore Ls (Grey) and Lr (Orange) wires are redundant on the zone valves.

A 10K ohm resister will be fitted in place of cylinder stat connection at ST8 to ‘fool’ the boiler in to thinking the water is at c.30 degrees. (https://www.youtube.com/watch?v=i_FIS8XRm-I)

The Cylinder Stat will be connected in between the HW BDR91 and the HW Zone valve to provide the fail safe.

The Priority Domestic Hot Water setting on the Evohome controller will be enabled and the temperature control/firing up of boiler is done via the OpenTherm bridge (R8810A1018).

So here are my questions:

1. Will the above proposal work?

2. Do I leave the link between LR and LS on ST10?
Although I’m not fitting a Worcester Wave, I assume a similar procedure as it also uses the EMS/BB terminals, according to the installation manual, the link between LR and LS need to be reinstated if replacing existing 230v controls with this. (https://www.worcester-bosch.co.uk/profe ... ructions-1)

3. Do I need a twin channel Fascia Controller like the DT20?
Having watched MWPHS video: https://www.youtube.com/watch?v=ubT-I7zE3k4 he was also unsure if it was needed but installed one anyway (note. the boiler in the video has the integral diverter valve which I am trying to fool my boiler in to thinking it has one, I don’t have a problem spending a few extra quid to get one, easily sourced used/refurbished on ebay.)

4. Will I need to factory reset the boiler after rewiring to the new schematic?

5. Have I missed anything, can anybody suggest improvements, concerns, or general advice?

Thank you,

Zak

[Richard]

Hi Zak,

As you have tagged both my videos in your post, it probably figures I have all the answers. Unfortunately when it comes to the CDi using an OpenTherm adaptor, sadly I don't.

As you can see in the latest CDi video I did ( https://www.youtube.com/watch?v=ubT-I7z ... uv&index=4 ) I wasn't sure if it needed the programmer when operating with 230v switching and the integrated diverter, so I bought one quite cheaply off eBay. One reason was to fill the gap when I removed the comfort controller, and the second reason was to ensure I was in and out of the property in one installation session.

Sadly I don't 100% know what will happen when you do what you propose. The LS/LR link is there to give the boiler heating demand out of the box.

Only point to note is that the front metal casing on this boiler is the primary gas seal so should only be removed by a Gas Safe Registered installer (like me).

Good luck with it.

Richard

[zak1981a]

Thanks Richard, it's a shame you are so far from Nottingham otherwise you'd be the engineer I'd bring in to have a play with this! I will get a gas safe engineer to come and have a go with this proposal, also happy that you didn't outright say it 'won't' work... best thing to do in this case is crack on and see what happens. I will respond here with results.

Zak

[zak1981a]

Posting a reply to confirm it works!

I carried out the work under the supervision of a gas safe engineer.

The code plug 1002 does indeed provide power/enables the BB terminals on ST19.

It did not initially work because I didn't link between LS and LR which is required (so assumption that this install; R8810A > OT-EMS Converter > Boiler BB terminals, should be similar to the Worcester Wave installation manual is correct).

I did not need a twin channel fascia like the DT20.

I did not need to factory reset the boiler.

I'm quite pleased with the result, will monitor and report any issues.

[Richard]

Thanks for the update and the details! There was no reason it shouldn't have worked but I'm super glad it did!