I'm very happy with the heat pump service from Cosier.
A different company installed my heat pump but I'd had a nightmare trying to get them to come back to do a service. In contrast, it was easy to book a time with Cosier, and the engineer Mark turned up on time and thoroughly cleaned the outdoor heat pump. He showed me how the fins behind the fan had become dirty over time and that the heat pump would be working less efficiently as a result. Mark used some cleaning fluid to clean the heat pump itself and showed me the dirt that was starting to build up in the magnetic filter. After cleaning everything, he spent extra time going through the settings that my original installer had set. He noticed that the hot water had been set to run 24 hours (which was expensive), and set up a schedule so that it would only do the hot water heating in the night time when I get the cheapest rate on my EV tariff. He also set up "weather compensation" and explained how this would allow the heat pump to run low-and-slow instead of on-and-off at the fixed temperature set by the original installer. I got the feeling that my original installer had just left the controls on default factory settings instead of trying to optimise it to give me the lowest running cost.
I'll be using them every year from now on.