Help with wiring - Changing Wireless Receiver to Extension Kit to get Opentherm/modulation in the UK

richrodgers

Hi

I currently have a V3 wireless receiver connected to a Worcester Bosch Greenstar 34CDI Classic combination boiler, which supports modulation via the EMS bus. This seems to be supported by Tado, but only with the EU version of the wireless receiver or the older Extension kit.

This is controlling by 2 TRVs and everything is working as expected.

If I get hold of an extension kit to replace the existing wireless receiver, I want to understand what I need to do with the wiring to swap the two over. Can anyone advice please?

This is how my current wireless receiver is wired.

And these are the wiring options on the extension kit that I grabbed from another post.

I need to connect the + and - to the EMS bus on the boiler, but I'm unsure whether I should be using the "Potential Free" option or the "Switched Live" option.

I can switch the L and N, but I'm unsure on the rest.

If it's the "Potential Free" option, is it a matter of swaping the "CH COM" from the wireless receiver to port 1 (COM) on the entension kit, and then moving the "CH NO" wire to port 4 (NO).

If it's the "Switched Live" option, what do I need to do here?

Thanks in advance.

Rich

johnnyp78

You’re not using either. Connect + and - (far right) to the ems connections on your boiler. This may be enough to power the extension kit, if not wire in l and n.

richrodgers

Thanks.

I probably should have mentioned, there is a single CH outlet from the boiler that is then split in to 3 zones which are controlled by individual switches.

I'm assuming I need to use the black and grey wires in the extension kit somewhere to switch the correct zone on when the radiators call for heat?

GrilledCheese2

@richrodgers You cannot do EMS with multiple zones. You need to stick with 230V relay mode to control the zone valves. The alternative is to revert the pipework to a single zone and use TRVs on all radiators for zoning. This will allow EMS to be used.

johnnyp78

How are the switches controlled now? In most zoned systems they would be connected to wired thermostats, which would operate the relays. Or does the boiler control them directly? As far as I can see the only wiring on your current wireless receiver goes to the boiler.

richrodgers

Thanks.

My current system is a mess for various historical reasons, I have 1 zone with 2 Tado TRVs and a wireless receiver, then I have a underfloor heating zone on a Nest, and a separate underfloor heating zone on a Honeywell Wireless thermostat.

I'm looking to consolidate them in to a single system, ideally that supports modulation on the boiler but I'm not sure there's an off the shelf option that works. Does anyone know if there are any options?

I've read that Evohome supports modulation with multiple zones, but it's Opentherm rather than EMS. There's a converter you can buy that allows an Opentherm system to talk to the EMS boiler but I can only find a single instance of anyone trying this and they said it didn't work very well. Anyone got any experience of this?

Another option may be to get an EMS gateway (https://bbqkees-electronics.nl/) for Home Assistant and see if I can control it all that way. I currenlty have all three systems linked in to Home Assistant and can control them that way, I just don't have the EMS gateway.

Any thoughts?

johnnyp78

I don’t know for sure, but presumably Worcester Bosch make some kind of control of their own to do this? Regarding Opentherm, given that it’s a requirement to have it in the Netherlands I would imagine any boiler also sold there would have to have a decent EMS to Opentherm conversion kit available. Just supposition on my part though.