"Christian McArdle" wrote in message
. net...
Note though that even cold fill only can still knacker a shower
in some cases. If you mains flow is marginal, turning on a cold
tap will reduce the available flow to the combi causing a
temperature rise in its output.

If it is that marginal, then a mains pressure cylinder/heat bank, would
suffer the same effect as a combi, too.

Exactly. More thought is generally given to unvented cylinder and heat bank
installations. Far too many combi's are just slapped in teeing off the
nearest cold mains pipe for its supply, giving them a poor reputation.