The problem I am having is who is telling the truth. Panasonic say that a buffer tank should be fitted as part of the installation requirements. The installer is saying on his commissioning paperwork that there are 50ltrs water volume so doesn't require one. As an ordinary householder how do I know what is required. He says that he has fitted over 300 heat pumps with no buffer tanks. I am know faced with a bill to put this right by another installer.