As well as the treatment plant, we have one other system that we have no remote monitoring for - the hot water system. It's an Air Source Heat Pump with a 300 litre water tank attached and seems to work very well for us. Of course, it's now been in use for several years and so we're interested in monitoring it for any signs of trouble. It has already thrown a few errors and needed some TLC.

We recently had to change the exhaust fan which was making horrible noises and sounded like it was about to fail. The one we removed certainly showed it's time in the machine :-)

However, while changing the fan and rewiring it to the logic board I noticed a couple of connections weren't in use.

We had already been told that in order to view remote data we needed another module which we didn't install. Had we installed that module we would enjoy MODBUS access - which would be ideal for keeping an eye on things. Apparently this other module was connected via  a simple cable.

What are the chances that a module that provides MODBUS externally wouldn't also use that protocol for inter device communications? After searching for a while (the system is manufactured by a Germany company and much of the information related to it is only available in german) I found some images of schematics related to the system that confirmed my suspicions. The hot water system has a MODBUS port and by examining the settings I could even find the information I needed to communicate with it.

Armed with a trusty RS485 to USB adapter I connected to the port and queried the device. It took a couple of attempts to figure out the correct connections for the port (A, B & GND)  but then the MODBUS magic happened. :-)

I haven't found any details of the registers and their meanings online yet, so armed with some information from the system and some register dumps I will need to slowly piece things together.

It's good to finally have some visibility of the system.

If only the treatment plant had been as simple...