Puller has yet to tell me where these huge accumulations of sludge come from in all these systems he has come across.
Then allow me. It is the large expansion volume that a large cylinder of heated water will require. A large volume of water is displaced into the expansion tank where it absorbs oxygen from the atmosphere. On cooling the water is drawn back into the system and the oxygenated water causes corrosion. Sludge is the product of that corrosion.
The Powermax was a sealed system and had no corrosion problems SFAIK.
Onetap you have failed repeatedly to answer my questions on what combi manufacturers do about 60 degree delivery.
I answered your question, but you were too busy arguing about a point I had never made to notice.
All the combis are capable of producing water at 60 degC at reduced flow rates and this should pasteurize any legionella or biofilms that have colonized the pipes. If you were to ask the manufacturers about the recommended distribution temperatures, they will refer you to L8, or give you the same information that is in L8. Anything else would expose them to legal action. You try and get one of them to give you a written recommendation for a distribution temperaure of 50 degC or less.
The data you posted was for a bare heat exchanger and it was written to give a misleading impression of the PHX's performance.
The requirements in the Water Regulations are stored at NLT 60 and distributed at a temperature of NLT 55 degC (strange that). However the guidance G18.2 also says; "This water distribution temperature may not be achievable where hot water is provided by instantaneous or combination boilers."
It doesn't say what hazards associated at distributing at less than 55 degC are, and it doesn't give you a 'Get out of Jail' ticket if someone gets legionnaires' disease from a combi boiler system you've installed that couldn't achieve 55 degC. If you were to set a legal precedent on this, I'd expect you might spend some time inside.