I had a new house built 4 years ago with a solar panel system for heating domestic hot water and an air source heat pump to supply underfloor heating with 2 zones and individual room thermostats. I have had continual problems with the heat pump. when the system works it is fantastic. The company that supplied the system say there is nothing wrong with their system. However the heat pump fails every winter, the company that are responsible for it have replaced it 3 times but every November it goes wrong. I have just waited 11 weeks for the latest machine to be repaired which happened last monday and it hasnt worked since repair (they have not come back to look saying they are waiting to check something on the buffer tank) I suspect this time it needs gassing up with refrigerant as this has happened before. i have back up immersions on both water tanks but only use these when the heat pump fails. I need an independant knowledgeable engineer to carry out an inspection to get to the cause of the problem,or some thoughts from engineers who have encountered similar issues as this is intolerable.