Having avoided looking too closely at the system for the past 11 years, I think it's time to investigate the settings. 

The ashp is a Mitsubishi puhz-hw140v with a Danfoss controller and wireless thermostat, the controller

is old school, not computerized.

I'm not quite sure why the package avoided using the timing functions on the Mitsubishi controller.

Since I changed the TP4000 default factory setting for condensing gas boilers, apart from the occasional

failure of the wireless link, all has been ok otherwise.

The house is rated at E, area 154m2 with total heating and hot water requirement estimate of 34,230 kwh.

Location is in the southern part of Bucks, not so far from High Wycombe.

Annual electricity consumption is around 10,000 kwh, of which I would think 60% is for heating.

Originally I've had some trouble with the pressure on the dhw system, and issues with the pressure vessels

loosing air, I had to fix these myself as the installer is no longer available and our plumbers don't want to

know.  The main issue I can see is that the ASHP has developed a list of around 6 degrees due to

settlement around the wet end.

I would love to hear any recommendations regarding maintenance & servicing.