Worcester Bosch Boiler Modulation

[DerekPCB]

Hi, just after some advice. I am looking to upgrade our heating and hot water system to use smart controls. Any help answering the below questions would be appreciated and set me up for further research.

The house has a Worcester Greenstar 30CDi Classic Regular ErP boiler, hot water tank, and a Honeywell programmer and thermostat.

* Does this boiler support modulation?
* Can it support OpenTherm, and if not, is there an adapter that will make it work with one?
* I had a look online, and taking Tado as an example, for WB boilers, it supports R1 (relay on/off) and HT-Bus (D17). While I understand the simple relay on/off will just turn on the boiler calling for heat, what is the advantage of using the HT-Bus? Is it equivalent to opentherm?
* Is boiler modulation actually that more efficient than using it without? I imagine the real benefits are when weather compensation can be utilised. However I think this boiler will be too old for that, but again maybe if I could get it to work with Tado, or the like, then that becomes an option?

Any thoughts welcome.
Cheers

 

[MNW67]

I can't answer all your questions but I might be able to kick things off.

Your boiler will already modulate its power output automatically between about 8kW and 30KW. But I think you might be talking about using a modulating thermostat. I honestly don't know whether it can. On their regular boilers Worcester Bosch seem to restrict some of the more interesting functions. I don't even know if it can do weather compensation.

Greenstar CDi Classic Regular ErP Installation and Servicing Instructions | Worcester Bosch

central heating boilers, combi boilers, gas boilers, oil boilers, gas central heating, heating engineers, boiler installation, boiler repair

www.worcester-bosch.co.uk

 

[muggles]

Yes, it's a modulating boiler, albeit not a very good one at just over 4:1. It doesn't support OpenTherm, Worcester want you to use your own modulating controls, although even then you can do very little with the Regular boiler.

 

[DerekPCB]

Appreciate the responses.

But I think you might be talking about using a modulating thermostat

Do you mind explaining the difference between modulating thermostat and boiler self-modulating?

Worcester want you to use your own modulating controls

Potentially EasyControl is compatible with this boiler but depends on the manufacture year - https://www.worcester-bosch.co.uk/downloads/bosch-easycontrol-brochure.pdf. However, I've yet to see if I want to invest in a smart system from themselves and forever be tied to one manufacture.

OpenTherm has to be the way forward, and I noticed there is an adapter but I can't find information if 1) it's compatible with the Greenstar 30CDi and 2) that tado and the like will talk to it properly.

So I think that leaves the option of using the relay on/off with a new smart controller, or whatever HT-Bus (D17) does.

 

[MNW67]

Do you mind explaining the difference between modulating thermostat and boiler self-modulating?

In the standard set up with an on/off room thermostat, as the boiler approaches its set flow temperature, it will modulate down to a lower power output and will try as hard as it can to stick to that set flow temperature.

What I meant by a modulating room thermostat is an OpenTherm thermostat or a thermostat using one of the proprietary bus connections. In those set ups, the boiler and the thermostat constantly talk to each other and modulate the power output and flow temperature in order to maintain the temperature set on the room thermostat.

 

[MNW67]

Potentially EasyControl is compatible with this boiler but depends on the manufacture year

Do you mean the following table. A system boiler is different to a regular boiler.

 

[DerekPCB]

Do you mean the following table. A system boiler is different to a regular boiler.

Yes that is the table. I appreciate they are different but from the table, both the Greenstar CDi Classic and Classic System are compatible. But I now see that "Classic Regular Erp" is not listed.

While I do have a hot water cylinder, I actually have not been in the loft (new house) to confirm if I have a cold water tank.

 

[muggles]

Yeah there's very little you can do with the Regular unfortunately. It's an expensive boiler with a very poor feature set

 

[DerekPCB]

I think it's then a case of just getting smart thermostat for heating and hot water, and using either relay or the HT-Bus for simple on and off. While the boiler is working, I don't want to rip it out just for the sake of modulation. Hopefully next generation will all be modulating with weather compensation and open standards.

 

[trickyearlobe]

@DerekPCB , sorry I'm a little late to this conversation, but maybe I have useful info for you, or other late comers.

First off, there there are a few very similar looking versions of this boiler around with similar names.
None that I'm aware of directly support OpenTherm as Worcester Bosch group use their own proprietary EMS1, EMS+ or EMS2 protocols.

If yours is the model designated by GC as 41-406-33 (small label inside drop down front panel) then it doesn't appear to support EMS or any other smart bus (see installation manual page 28 which can be downloaded here). If I got the wrong boiler and you can see terminals marked BB or EMS you're good. To have a look, just undo the 2 screws at bottom/front of the cover and lift it off (see instructions in manual), then free the catch to drop the front panel down. A couple of screws get you to the electrical connections.

I have a similar model but it's a combi without seperate HW tank (A Greenstar 38CDi Classic ERP) which does talk EMS1.
You can see the EMS connections marked BB top right of circuit board on page 30 of this manual

It self modulates to achieve desired "flow temp" which should not be confused with "room temp" or "room setpoint". I set mine to a flow of 55-60c depending on time of year. You need return temps to be 55c or lower for the boiler to run in condensing mode (most efficient).

I have a Nefit EMS to Opentherm adapter part number 7746901847
Obtained from Plugwise in the Netherlands (currently out of stock but they ship to UK as do a couple of others)
Nefit is part of Worcester Bosch group so it's a legit converter (specifically for NL since they require all boilers to support OT)

Control is done with my Wiser heat hub
It talks OpenTherm to the boiler through the Nefit adapter
It manages my schedules and modulates the TRV's (they open in steps from 0% to 100%).

Wiser TRV's/Stats --> Wiser HeatHub --> Nefit OT to EMS --> Boiler

I also have an interesting gadget attached to get boiler stats using an ESP32-S3 running EMS-ESP32 with a BBQKEES interface board
It appears to be telling me that the boiler is accepting on/off commands, but it's completely ignoring the modulation commands from the Wiser, telling it to lower the flow temp as the rooms all approach their set-points.

That said, I'm still getting better flow temps and steady room temps with about 30% reduction in heating bill using OpenTherm and some magic self balancing TRV bodies from Drayton... not bad.

I intend to try modify the EMS-ESP software to directly emulate the WB Easy-Control thermostat/controller to see if the boiler will accept modulation commands from there (since EMS has different bus addresses for different classes of device and the Nefit adapter is classed as gateway rather than thermostat or ). If it does, I will need to build a replacement for the Nefit adapter (or figure out if I can flash it with better firmware).

 

[trickyearlobe]

Forgot to mention... specific model of Tado V3 (but not Tado-X) support EMS1 (but not EMS+ or EMS2) directly with no converter.

A lot of the early V3's sold in UK don't have the EMS interface as UK plumbers just wire as on/off switch even if OT is available.
Later UK V3's do have EMS/OT
All EU V3's have EMS/OT

Tado-X only supports on/off or OpenTherm.