Hold the phone, now I don’t want to jinx this but in the process of balancing my system (or at least trying to) I thought I would go down a different tack and used decorators caps instead of the TRVs (sorry @toodles I failed miserably at following instruction although it is an excellent guide!) I popped out a thermal camera and took a look at all the rads and two were completely off (TRVs were seized closed), no idea why but they are now fully open (obvs checked all the others). All lock shields are now fully open and the three upstairs rads have been closed down via the decorator caps until the rooms were a degree colder than the downstairs. The two massive uprights in the kitchen are set to 2 on their TRVs to offset the Aga now the whole house is at a steady temp every room is within a degree and the best thing yet is I have had a steady run for the past two hours! My COP is through the floor but at 800-ish watts with the compressor at ~30hz I am heating a 4 bedroom 1970s dormer bungalow! 
my WC settings are 38@-3c and 26@25c (no idea how I have ended up at these!)

@steam-powered keep the faith it can be done although yours may take a bit more finesse as it is so massively oversized!

@grantmethestrength Well done! Progress indeed, and if the TRV decorator’s caps do the job - good oh! You mentioned a TRV was jammed, this happens and is usually cured using a flat piece of material (coin or some such) resting on top of the projecting pin; the coin is then pushed down then released - repeat, repeat, repeat until the pin can move up and down smoothly and freely. I’ll let you off for not managing the LSV procedure successfully!😉 Toodles.

@toodles Billy the big bahco spanner lovingly applied (gently of course and not too vigorously) worked a treat!

@steam-powered that’s all really interesting. My experiment of a lower flow temp at the cold end didn’t work out, the house lost too much heat so I’ve moved it back to 34 @ -7. Similar to yours mine ticks over nicely using 600-700w in the 5c and above zone although when it gets to say 12c it is losing so little heat it’ll long cycle which is fine by me as using the detect setting is working fine. At 4c and below it cycles about 1.5 to 2 times per hour, I can affect the length of the cycle by changing the hysteresis but if I make that too long the average temp drops. So still no wiser as to why it won’t just run at the lower temps

@grantmethestrength that looks interesting, can you share the info on accessing the modbus and HA please? How old is your Aerona 3?

@damonc my Grant was installed in Jan this year (however no idea of how old it actually is). In order to access the modbus you need to buy some additional equipment and run some ethernet cable out to your unit. For just monitoring and basic modbus control (like WC adjustment , WC on/off, flow temps etc) you only need two wires (three if you want to use the ground but this isn’t necessary).

I initially went for the Waveshare PoE ethernet to modbus adapter others have gone down the usb adapter route. I then discovered if you want to control/automate more of the functionality you actually need dry contact relays. So if you wanted to say control night mode or low tariff mode, or DHW on/off or dual setpoint (really handy if you have only one zone you can set up an entirely different WC curve and just toggle it on/off for say an extreme weather event).

I tried permanently bridging those contacts hoping to be able to just use the modbus registers to turn them on/off but this didn’t work so I went with a waveshare 8 channel PoE relay. This set up is working but I am now looking at esp32 solutions to stream line the whole thing.

You can find my guide on my github repository

You can either set up the built in modbus integration in Home Assistant and expose the entities that you will find useful (just copy and paste my yaml files) and build some impressive cards/dashboards. Or use my integration (or for that matter fork my integration and make it your own).

However take a deep breath!

I then really went down a rabbit hole lol with various PoE esp32 controllers (Olimex, LillyGo were strong contenders) and various relay set ups.

I even made a touch screen controller using the waveshare 7 inch touch display with rs485 controller for local control independent of home assistant (but feeds into it).

Seeed Studio have an esp32 rs485 addon which is tiny, as long as you have power for a usb c cable and wifi connectivity at your unit you could mount this close to your unit (in a suitable container) and run a short ethernet cable to your unit.

or if you wanted relays add a solid state relay. I have found I only need 4 channels for my set up (DHW on/off, Dual set point, night mode and low tariff mode). that is an apple trackpad for scale.

However if you wanted a really simple all in one solution the M5Stack STAMPLC is awesome it is din rail mountable so will fit into a waterproof housing 4 relays built in and also has expansion ports for stuff like external sensors etc.

As I say this is a massive rabbit hole, but I have really enjoyed the journey, I am probably going to build out the touchscreen project, and STAMPLC as stand alone projects (the same code will work for the Seeed Studio) but then combine them so that the touch screen becomes a controller (HMI) for the once STAMPLC. Once I finish the code for the touchscreen, Seeed Studio and STAMPLC I will post it to my github. 

and breath!

Oh badgers nadgers! I knew I would jinx myself! It turns out my joyous rapture was short lived, 2.5 hours and then back to cycling. But then again the house is warm, and it is still costing the same as running a small fan heater to heat my whole house. So mustn’t grumble!

@damonc, when yours is running at 4 degrees and below does the power consumption increase very much from the 700W base level? (I would expect an increase to say 900-1100W) 

Mine leaps from 700W and perfect modulation at 6 degrees to 1500 - 1800W at 5 degrees and below. Do you see the same big step change in power consumtion?

Mine then also just fails to modulate below 6 degrees, and after only 8 mins goes over the flow temperature target.  Do you see anything like that?

I would almost be happy with your 1.5 to 2 cycles per hour compared to the 6 to 7 that I have below 6 degrees!

To my thinking, if the control system can modulate well at 6 degrees it should be able to do the same at a lower temperature, even though the pump will be running at higher consumption.

Posted by: @steam-powered

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To my thinking, if the control system can modulate well at 6 degrees it should be able to do the same at a lower temperature, even though the pump will be running at higher consumption.

Are you certain that the cycling you see at lower temp isnt just defrost?  Below 5 defrost would be expected!

@steam-powered yes about 1-1.2 kw. I’d expect the same I don’t get why it can’t modulate smoothly it’s almost as if it has modulation steps. Maybe something Grant can advise on?

@jamespa that’s possible I guess, is there an automated defrost limit temp?

Posted by: @damonc

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@jamespa that’s possible I guess, is there an automated defrost limit temp?

There is, you cant change it.  

Expect regular defrost at any temperature less than 5, until it gets really cold and the air dries out (-5~-10 or less).

You can tell its defrost because 

• the fan stops working temporarily
• the flow temperature drops sharply, even to below the return temperature
• at the end of the defrost cycle you will see a (often quite impressive) cloud of water vapour being pushed out the front of the unit
• the compressor will often ramp up to max immediately after in order to recover as soon as possible

Frost builds up on the evaporator fins at the back of the unit and needs to be cleared from time to time.  Thats what the defrost cycle does, by robbing a bit of heat from the circulating water to melt the ice.