Just did a trial with the thermostat forced on. Set flow target to 26 and 3.0 Deg overshoot. Heat pump for just over an hour at 12 degs outside. Then it took a break for 1.5 hrs. So got a great increase in run time, have now reduced the overshoot to 2.5 degs to see effect. Will leave it running the rest of the day to see what it does and what it does to the house.

@derek-m So I turned up the warm weather end of the WC curve to 33 C flow temperature and made sure the spare bedroom radiator was on. The cycling seems to be less now and probably within tolerance. I will have to check how to make some of the setting changes suggested with a Samsung and see how that affects things.

Thanks for all the help everyone.

@bontwoody I've previously heard a rule of thumb to limit to 3-4 start/stops per hour. 
Maybe a stupid question: Do you need the heating today? How warm is it inside the home?

@hcas We were using ours yesterday as we felt 19 degrees C was just too cool with the addition of the rain! (South East England. Regards, Toodles.

@hcas Well I guess that always going to be a subjective question 🙂 I do feel the cold as my circulation in my extremities isnt the best, but actually it was my wife who wanted it on today.  Its 22C indoors now which I know is way too hot for some, but we are never going to be comfortable at 19C like a lot of people. (Kiss my high COP goodbye!)

The heat pump is drawing less than 400W and our solar panels are producing way more than that so it is purely a matter of comfort rather than cost.

@bontwoody That is pretty much the same as our situation; our comfort level is 22.5 degrees C. and 19 with rain just does not cut it for us! Toodles.

@toodles At least we are living proof that heat pumps can heat a house toasty! 🤣

Totally makes sense @bontwoody and @toodles! Comfort is #1. Location and person dependent.

With that in mind, you'll always have some cycling during milder weather. But based on your graph, looks like that is now under control.

We heat the house to 24-25 all winter and keep it at 22-23 the rest of the summer. The heating has been on for around 17hrs a day these last few days with the rain. We’re in the south west.

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We heat the house to 24-25 all winter and keep it at 22-23 the rest of the summer.

Our last house was similar, but this one is very well insulated and UFH throughout, now above 21 is starting to get a little to warm. Normally once the average temp increases to 10 degs that's when our heating goes off. Taking advantage of the cool July (11 today) to fine tune some cycling. 

Back on topic.

Did some adjustments yesterday. Increased the over temp margin above target temperature to increase run time got an hour+ run. Which is to long. But didn't restart again for over 18 hrs. So reduced the upper stop margin to 2.0 degs, but also decreased the undershoot temp to allow a sooner restart. Looking ideally for a 15 to 20 min run but not a massive off time other the summer houses too much. Bit of a balancing act.

Made some adjustments based on information provided here and on buildhub.

Prior to stating

Below Target start delta was 8 degs

Above Target stop delta was 0.4. 

Target flow temp 30.2. with a small WC curve rise to 35 flow at -3.

This morning it was close to 11 degs, which is above where I would normally heat. After some tuning got to 2 starts per hour and a 15 to 20 min run time. The sun came out at lunch and the heat pump hasn't restarted, living room at 21.6. ASHP return temp is sitting at 21.1. which is good as it's now self managing and matching output to required load 

So setting are quite different 

Below Target start delta is now 5.8 degs. Was 8 degs

Above Target stop delta is now 2.0 degs. Was 0.4 degs.

Target flow temp 25 at 14, with a WC curve to -5 and max flow temp of 32.6 degs. (Think the 32.6 may be a little high, but too warm to test)

Upside is it should run without any house thermostats and generally look after it's self. Once room temp is at 21 or above the heat pump should not get a permission to start heat. Have set the circulation pump run continuously, when not heating the flow rate drops to minimum flow, so should pull very little power.

Just need some warm weather to set up cooling.

So the take away are 

 1. An aspect never discussed is how the heat pump responds to target flow temp, and how this managed. Been through lots of different manuals to see what they say, most are silent.

2. What manufacturer default to, may be miles away from what is needed.

3. You don't have to suffer short cycling, it fixable with a little time.

4. Base running target temp has been reduced a whole 5 degs - which should see an uplift of 0.5 in CoP.