Home assistant for the Worcester Bosch boiler? Raspberry Pi 5 and SSD.

We've had a Worcester Bosch Greenstar Highflow 440CDi combi boiler for a decade or so. This is a floor standing boiler that's a bit larger than most of their range. The reason for this isn't because it's an ancient old beast but instead because it is a so-called "High Capacity" model. The actual primary heat exchanger is nothing out of the ordinary 

The installation and service manual gives a pretty good idea of the construction and internal appearance.

In particular, what differentiates this model from more normal wall mounted models is a "heat store" and a slightly larger water-water heat exchanger. The heat store is simply a small water reservoir that keeps a volume of (hot) system water up at temperature to reduce the delay in hot water appearing. You can turn this off and on from the dedicated Bosch "EasyControl" remote thermostat.

The promise behind the larger water-water heat exchanger is that you can run multiple hot water consumers simultaneously with less chance of losing temperature control eg run 2 showers / baths at the same time. In practice, this means the plate-type heat exchanger simply has 20 plates instead of the more normal 14 plates. Big deal.

The heat store comprises a 45 litre tank that is held at system temperature (perhaps 70C, depending on where the controller is set). When hot tap water is required, the incoming cold water passes through the plate heat exchanger, which means there's no delay waiting for the gas-fired heat exchanger to fire up.

Bosch sell a range of associated products such as the Wifi-connected thermostatic radiator valves (TRVs) but of course, being Bosch, they have it all tied down so that you have to use their products and can't integrate it easily with systems such as Opentherm, Home Assistant etc. 

I want to be able to access and edit the myriad settings within the boiler. Currently, it's only possible to make a few changes to some of the main parameters. For instance, I can set the flow and hot water temperatures from the front panel using the yellow knobs - but there's no numerical indication of the resulting values. Similarly, I can change the room setting temperature and schedule at the wall-mounted EasyControl thermostat but again, there are no other parameters I can see or change.

Currently, the boiler is "modulated" by simply turning it on and off using a simple hysteretic scheme within the thermostat, with the boiler flat out at full power when it's enabled. A more intelligent algorithm might modulate the flow temperature closer to what is actually needed to maintain room temperature and little more. In this scheme, you might expect the boiler to remain on longer but at lower temperature, resulting in reduced losses from the pipework and the boiler itself. There's also the option to account for changing outside temperatures using external sensors or internet data. 

From what I can tell, many more possibilities have been explored and implemented within the Home Assistant / Worcester Bosch user community. However, this requires getting free access to the internals and also a means of monitoring and editing the parameters.

3rd party bridge - BBQKees:

Luckily, there are 3rd party products that provide a means of accessing the internal functions of the Bosch controller. This acts as a bridge between the external (open source) devices and the proprietary Bosch controller. The Bosch system uses a 2 wire "EMSbus" serial link which communicates with external devices.

One common means to bridging to the Bosch controller is the BBQKees "Gateway E32 V2 KIT (Ethernet + WiFi Edition V2 KIT)" This is made a Dutch company and seems to have reverse engineered the Bosch protocol.

The red connector plugs into the Bosch control board and it communicates by wifi or ethernet to your main system controller, which may be a platform such as the Raspberry Pi running Home Assistant.

I looked into this briefly back in 2018, more out of curiosity than anything else. It struck me as more of a geek thing than a serious application - or to put it another way, I couldn't see any sensible use for it in my domain at the time.

The Raspberry Pi Foundation offer an imager that loads a range of OSs suited to your specific RPi model. I've got a selection of Pis going back to the original but for this application I've got myself a Version 5 with 4GB RAM and an 8GB microSD card.

There's a new version of Home Assistant coming out very soon (tomorrow?) but for now, I'll install the current v18.3 (2026-09-27). If it actually goes easily I can always come back later and update it to the new version.

Naturally nothing is easy, so there was some buggerage required before it installed. I don't have any means of plugging in the ethernet connection, so I need to use the wifi instead. To do this, I need to let it know the wifi credentials:

1. Name a USB stick CONFIG
2. Create a folder called network
3. Create a file called my-network (no .txt suffix) containing the following, changing the network name and password to suit:

[connection]

id=my-network

uuid=5f3c2a1e-8b4d-4e6f-9a2c-7d1e0b3f4a5c

type=802-11-wireless

[802-11-wireless]

mode=infrastructure

ssid=YourNetworkName

[802-11-wireless-security]

auth-alg=open

key-mgmt=wpa-psk

psk=YourPassword

[ipv4]

method=auto

[ipv6]

addr-gen-mode=stable-privacy

method=auto

Then insert the USB stick into one of the RPi ports and reboot.

Looks as if that went OK. Now come back later and see if it completed updating to the latest version. This should give me the basic Home Assistant platform, ready to interface with the BBQKees bridge when it arrives next week. I can then start to play with the boiler and look at possible extensions to the system, such as wifi-linked radiator TRVs from suppliers such as Tado. Obvs, the Bosch TRVs only work within their closed, proprietary system. Fuck 'em.

That went well, although the 8GB of microSD card ended up close to full with just the std Home Assistant installation, so when I got to the point of trying to install actual apps or do a dummy run backup, I found there wasn't enough space left at around 1.2GB.

So I've ordered an "M.2 HAT+ Compact" 

and a WD SN740 256GB SSD M.2 2230 30mm NVMe PCIe 4.0 Gen 4 x 4SSD to go with it. 

The idea is that the small (30mm long) M.2 SSD will fit within the red and white Pi case.

256GB should be more than adequate but it's the smallest 2230 size SSD I could find. It should also be a fair bit faster than the microSD card it will replace.

Anyway, let's see how that turns out when it arrives tomorrow. Those two items come in at £102, on top of the £160 I've already coughed up for the Pi 5 kit and that kit didn't even include a microSD card....

Just think - the RPi was conceived as a low cost starter kit for school kids. Now it costs more than an entry level PC and several times as much as other SBCs...