Ah yes, I see you have the MIM-E03AN, which pre-dates FSV#2093.
Correct. If water law as set up on #2011/2/21/2 would give a target LWT of (say) 38degC but you select +3 on the WRC, your target LWT will become 41degC. It’s just a more convenient way of making temporary changes than reprogramming the FSVs.
If you are saying that the circulating water temperature drops quickly when the compressor stops, then this is quite normal. Usually a minute or two after the compressor stops, the circulating pump does too (this run-on is just to cool a hot compressor down). Then the water temperature sensors have no flowing warm water from the emitters, so are exposed the the cold air around the outdoor unit and indicate a temperature drop.
I was looking at your post #42 here, For the avoidance of any doubt, Home Assistant (HA) is completely free open-source software - you don’t need to pay for it, as your post suggests. I think it’s a super package, written & maintained by some extremely able, knowledgeable, and willing Folk. It can be loaded onto most platforms, and can be used for a whole host of different applications. The only consideration is that it tends to be used for monitoring & control of anything ‘smart’ around the home - from security systems to mousetraps (yes - SmartHomeJunkie Ed made a smart mousetrap, here!) and as such, ideally needs to be on a platform which can remain switched on 24/7 - like a Raspberry Pi for example. A Windows machine will easily run it, but if you used your laptop for this purpose, of course, when you took it out of the home…
Because it’s so popular, there are hundreds of free-to-download integrations & add-ons available for pretty much any item in the home, all designed by volunteers who just want to make things work, and share their ingenuity with others. One installed, these little packages will often even auto-search your network for compatible hardware, and even create ‘sensors’ for you - all ready for use in your own-designed UI. The only payment option I’m aware of, is a subscription for cloud access (meaning remote control) but personally, I find that once set up, all operations can be automated, so I manage fine without the subscription. If I really need to access part of my system whilst away, I just use the individual apps on my phone, but this is a fairly rare occurrence.
This is a very helpful summary, @Sykes and thanks for posting it.
In fact, that post was written some time ago (early 2025, when the world was slightly saner than it is now) and my implication of cost was based on the Home Assistant website where you are invited to buy hardware (like HA Green) which does of course cost money.
I’ve learned a lot since then, including contemplation of an RPi, with HA (free to download, as you point out) in charge of operations, and I’d even started a shopping list of sensors and actuators to connect to it.
But by the time you’ve included a half decent RPi (4B, say) with its SD card and PS, and a breakout board and a few electronic components (pull up resistors etc.) to connect stuff, and a few sensors (e.g. room temperature) and actuators (e.g. a handful of smart radiator TRVs), you’re up to £500 or (possibly much) more.
Now that’s tough to justify against hard economics when your annual electricity bill is around £700. Plus I’d need to learn some sort of coding (Python or Modbus or whatever, maybe both ), and about DHCP and IP assignment , and all the jargon attached to comms platforms (can I operate a wifi actuator from a Zigbee sensor? Don’t answer - the question was rhetorical).
In short, it’s all very interesting from an intellectual viewpoint, but old dogs/new tricks etc., and since my setup ain’t broke, I’m not sure I should be asking RPi/HA to fix it…
This is exactly where I’m at right now. I’m a little less worried about the money, I wouldn’t need any smart TRVs for example, and see it mainly as a bit of a hobby, which I’m prepared to pay a little money towards, but getting into coding terrifies me. Even as an engineer (with mechanical bias) and with lots of people on this forum who I’m sure would be able/willing to help, it’s a complete unknown for me and knowing where to start is the hardest thing.
Happily for us, @jakeymd1, we have several fearless pioneers on this forum that we can consult. The latest, @Sykes, is going places that I (no angel!) would fear to tread. For example, look at his latest post Recommendations for running a Samsung 6th Gen with Octopus - #46 by Sykes. (I’m just hoping that I don’t have to buy a MIM-B19N to be able to write new FSV values from HA…)
), and about DHCP and IP assignment 
, and all the jargon attached to comms platforms (can I operate a wifi actuator from a Zigbee sensor? 
Don’t answer - the question was rhetorical).