In article ews.net,
"Doctor Drivel" writes:

When replacing a cylinder go for a quick recovery m,model. Part L is 'not'
quick recovery. They go by names of Super Duty Ultra Cal and the likes.

Don't do this unless you have a condensing boiler,
as it will force a non-condensing boiler into condensing
mode, and rapidly destroy it.

Also probably not a smart move if you have a mid-position
valve, as you might find the cylinder steals too much of
the boiler output for the heating to continue working,
unless your boiler has an output power well in excess of
the house heating alone (which is unlikely as the system
was designed to heat a hot water cylinder).

Quick recovery takes all the boilers output heat up very fast and are
cheaper to run. You existing boiler may not take full advantage of the coil
as the coil may be capable of taking a boiler much larger, but when you
change the boiler, in time, it certainly will show even more dividends.

Quick recovery cylinder is one part of a complete heating
system design. You can't drop one in without knowing the
rest of the system was designed to support it.

--
Andrew Gabriel