In message , Colin eclipse 2
writes
I know - done to death.. A customer has asked me this question. I have come
up with the following list. Any other thoughts - sensible ones.. no need to
start a debate about the merits - just need a list!

Conventional
Pros
Stored hot water - so water (hot and cold) available if mains supply
fails
Immersion heater backup - hot water if boiler or gas fails
Warm airing cupboard
Cons
Cylinder needs replacement (in this case to comply with building regs)
Storing hot water not as energy efficient
More complex controls
More costly than combi to install


Combi
Pros
High pressure showers without pumps
Only heats hot water you use
No stored water (flooding issue)
Frees cupboard space
Cons
slower bath filling
No warm airing cupboard

Combi pcbs are more complex and tend to be a bit more expensive than
conventional boilers

Conventional boilers (correct me if I'm wrong) tend to have an immersion
heater in the HW tank giving DHW backup

--
geoff