so 

So on this question of compressor longevity, I have a Daikin Altherma 3 11kw installed by Octopus and I found that when the weather was a bit warmer the other day, but cold over night, that the blue light on the MMI kept going out and the power consumption of the heat pump dropped from c.1kwh to a few hundred w/h. 

**all of below is my logic with lots of reading over last few years **

If the ASHP feels the return water is high then it will go from 'blue light' heating to 'no blue light# but water flowing into the pipes.  the very same as when it you set the water to heat in the middle of a room schedule.  have you noticed that the flow water is very hot ( its just finished a hot tank cycle) but it will now switch to heating the home again, the rads get hot BUT the blue light isn't on. = its using all the excess from pipe/buffer until it get to a low temp vector then starts the compressor to start bring the in/out flows to correct temps.

it will also do this "no blue light" water into the pipe is the outside temperature is ~<5 degrees., this is frost protect, I turn my off but is still overrides and keeps enabling it, as now in April 2026, it sunny and will not snow but the HP can't see the weather just temp so trying to protect the system from frost.

the modulation was at 5 degrees and the overshoot was set at 2 degrees.  modulation is good if you want to slow the system down to think before it want to cycle down - (I force mine to use fixed temp with -2 degrees room thermostate offset so my system never reaches temp and I increase my flow temp for overnight TOU rate, but this is off topic)

I keep my overshoot to 1 degree as I don't like the HP to increase its range if the temp outside drops , as I don't want the extra pull of power for very little gain.  - I control my flow temps manually, cop, scop isn't a target for me.

Their answer was to recommend increasing the overshoot to 4 degrees.   that from training they had with Dailkin, I had 6 engineers in my home during my install as it was so new for Octopus.

Am I right in thinking that the compressor has shut down when the blue light on the Madoka goes out and this is a bad thing?  Yes and no. - Yes as your paying for it from the grid, no as the compressor isn't working. which is a lesser evil - you decide.

If the heat pump knows what its target temperature is and it has scope with the modulation and overshoot settings to adjust, why isn't it doing so?  from my experience its logic is to meet middle ground, having it on say fancoil and it reacts too fast, all of this you can see/test if you do not use weather compensation , if you play with fixed you and really see what occurs to HP when your 'leaving water temperature is at 40 degrees' then you change it to 36. the system going panic mode - it increased the litres/m from say 7 to 20 to get the temp down to 36 as fast as possible  (like someone has a gun to the HP head) , & is so dumb it turns off compressor as it over cooled itself , system cools down to say 26 degrees. flow rate goes to 0  & then is uses ~1.5kw electric to bring the temp up to 36 degrees, then the litres per min at a high rate until about 20 mins, it all settles back down.~~AKA cycling 

again I have spent a lot time with mine, hard to jot down this in a post as its about 1 years worth of experimentation and now I don't change anything or care about performance, COP.  it just runs my house at 23 degrees and I am happy.

rely the compressor should be able to just work a bit less hard rathe r than going off or gradually adjust for the change in outside temperature?

Up to a point yes.  However every heat pump (and every boiler) can only turn down so far, ie it has a minimum output (which, in the case of a heat pump, depends on flow temp and outside temp).  If the demand is less than its minimum output then both boilers and heat pumps resort to cycling (ie periodically switching on and off) so that the output matches the demand on average. 

Different heat pumps have different algorithms to control cycling (doubtless the same is true of boilers).  Vaillant, for example, keeps track of 'energy integral' (the difference between target FT and actual FT multiplied by time, measured in degree minutes) to make the decision when to turn back on.  Doubtless boilers likewise have different algorithms.

at I'm not sure about is: if the outside temperature increases and the heat pump flow temperature based on the weather compensation curve drops to compensate, whether the Daikin is designed to switch off the compressor (and therefore the blue light on the Madoka goes out), whilst the water still circulates around the radiators (hence the much lower power consumption) until the flow temperature has dropped to that required by the weather compensation curve at which point the compressor starts again

I expect it to continue circulating, at least for a while, in order evenly to dissipate the energy in the water into the house.  As stated above the algorithm for turning back on varies from heat pump to heat pump

The other thing in these numbers that was interesting is row 2.  You might be getting a COP of 7.2, but why would your heat pump be running at all if the outside temperature was 21.2 degrees?   

With regards to line 2, could it be that the (demand) was not met and although the external temp was 21.2c (some solar gain no doubt) the actual home / room temperature was below the desired temp, this would explain why it would run, I can make ASHP run when outside is 35Deg C, you just create a demand.

I don't know about the blue light thing as we are not a Daikin specialist but it is worth noting for other areas of posts here that compressor and pumps are not the only current draw or power use your shelly device will see, most if not all units (even in the summer) can run a 200w heater tape to keep the oil in the compressor warm and ready for action, these tapes often run in pulses or stages, Ecodan does something a bit different and pulses the coil inside the compressor without running the compressor to create a little heat. This power use is often overlooked and can be noticed by the keenest eyes or the most active efficiency measuring.. Also all of the EEV / LEVs can periodically do little resets before running, again this is like the unit is getting itself ready to run, I am not sure if all units do this but I think most do.  

If with regards to good old short cycling you manage to get a lot more data, often the 1st place to look is the emitter offset of any heat load, its ok to blame the ASHP for short cycling but it is nearly always due to - oversizing, unbalanced emitters, incorrect emitters, incorrect pipework, incorrect flow rates and then maybe some back end programming. To know for sure you need to measure a lot and find someone who can tune your home heating like a Porsche!

These ASHP have little brains and can do things we do not expect but ultimately it is all calculations and programming to make sure the unit it ready to go, achieves the internal temperature required while trying to decide for itself the most efficient way to do it. Throw in an unbalanced circuit or a 12kW ASHP system on 9kW of emitters and half the programme will not work correctly.  

I hope this helps a little...

Their response was that it’s not something they see commonly, but they suggested two possible explanations for what you’re observing.

The first possibility is that the circulation pump inside the heat pump is still operating even though the compressor has stopped. In that situation you’d still see a small amount of electricity being used, but the outdoor unit would appear quiet because the compressor and fan aren’t running. They mentioned that the pump can sometimes operate on its own simply to keep water circulating and prevent freezing, particularly when temperatures are low.

The second possibility they raised is a configuration issue with schedules. They said that sometimes users or installers change the control mode (for example moving from water temperature control to remote thermostat control) but previous schedules may still exist in the background if they weren’t deleted when the settings were changed. In that case those schedules can still trigger behaviour in the system even though the main control method has been altered.

So in short, Daikin’s view was that it’s not necessarily anything abnormal, but they suggested checking whether the system is simply running the circulation pump without the compressor, or whether there might be legacy schedules still active in the controller settings.

Might be worth having a look through the schedule settings just to rule that out.

I've consumed around 13kwh's today including 2 DHW runs set at 50c in the early hours and 47c just after lunchtime.

I also run the heat pump flow rate 2c higher between 4am and 6am to utilise the off peak rate and get some extra heat into the house.

I am very happy with the consumption levels and the system is near totally silent. I can only hear the low hum of the fan running when very close outside. It is silent inside all of the time.

I can now hear my next door neighbours gas boiler inside our house as it is so noisy compared to the heat pump we have!

Yeah, I don't also. I had wondered why Matt Drummond's 8kw heat pump (the one at the top) has a very steady electricity draw. It must be (as I'm pretty sure) because he runs at a fixed flow temperature of 31c all the time.

The Daikin at the top is Matt Drummond's I'm pretty sure. There is a lot of posts by him trying to optimise and understand his Daikin HP. I followed this for a few months which helped enormously with my decision to choose  the same 8kw Daikin.

I'm pretty sure he now runs on a fixed flow temperature of around 31c.

I suspect this probably shows up as a steady draw, as the HP is not adjusting the flow temperature as the outside temperature fluctuates

The data was taken to see how low certain Heat Pumps modulate. It's one of the reasons I chose the 8kw Daikin as it's power consumption in the shoulder months is very low.

With your Maduka light going out, I wonder if your system is cycling (switching the compressor off), indicated by the blue light going out, or that you have hit the internal temperature sensor limit?

Mine hardly ever cycles and so the blue light is pretty much always lit.

I also turned the brightness level down as low as possible, as the led light gives of a very small amount of heat and can impact the sensitive temperature sensor.

So it is not cycling, which usually means the compressor stops and starts.

It seems the heat pump's power levels are discrete and it is switching between ~2kW and ~3kW when the desired output power is in between. I don't see any problem with that.