I have had a few of this heater and found the following to be true.The flow of the water through the system will have a dramatic effect of the heat of the water. An L5 will battle to produce hot water with a flow rate of 8 litres per pump if you turned the flow down to say 3 lit. a minute the water would be in the system longer, therefore produce hotter water. I said this many years ago on this forum when we first started this gas water heating . Everyone thought I had flipped. There are many factors that effect the heat and some are just lucky to get the right combination of flow rate and pressure. Unfortunately, some just have the factors wrong and have a bad experience. There is the heat lost between the pump and the brush head which is a major factor as to the heat hitting the glass. That why after four different systems I decided to go without. Breaking glass, failed hose fittings,busting hoses and pumps playing up. Its a lot of crap and temperature loss due to long hoses no thanks its just not worth it.