Unpressurised DHW only heat banks are available that do not even need overflow and discharge pipes. A doddle to fit. No explosions. You obviously never knew they existed.
So you did not know that they need an overflow?
That just shows that you have NEVER even fitted one!
With your level of knowledge thats just as well!
You also think they need no maintenance ! Anyone who knows about them also knows that they should be checked for leaks or any other defects AND have the inhibitor concentration checked and topped up as required.
I have a real name and a profile with my contact details.
Drivel has to keep his hidden because he does not have any name and he does not want to be contacted!