Again, I’m going to say something ridiculous:
The pumps are too noisy.
Clearly they aren’t really, but it’s so quiet where we live you can actually hear the glycol moving around and about 2% of the time it’s distracting.
It turns out there’s no real benefit to pumping the water around if it’s not getting heated, we may as well just let it settle and slowly warm up the place it’s in. The radiators in our house are a bit like having a big warm dog in the room. We’re treating the volume of the radiators like a buffer tank, the heat pump pushes water into them and then it heats up the building. We’re pretty open-plan so we can get away with it because we don’t get one room being very different from the others.
I’m surprised it doesn’t affect the comfort much. I suspect it’s because we turn the heat off pretty quickly so it doesn’t have time to overwhelm the room. I’ve certainly noticed that when it’s running continuously the rooms get oppressively hot.
I did some ad-hoc experimentation where I measured the radiator temps dropping and it was close enough to the fixed “return temp” sensor that I felt OK using it as a proxy.
Anecdotally I have a radiator about 300mm from my chair in my office. I lie my arm on it to warm up. When I find myself thinking “ooh, that’s getting a bit too chilly” I go to nudge the heat pump only to find that the algorithm has just turned it on or was about to in the next couple of minutes.
I believe that it’s all down to the magic numbers in the code which makes me sad. I want it to be more robust so it handles disruptions better.