I have just moved into a new house with a Megaflo CL170 & Potterton Promax
He controlled by a Potterton EP2002 - the problem is there's no user manuals
and I'm only used to night storage heaters and combi boilers.

So what is the best way to use this ?? I've switched the heating on the
EP2002 to ON and the hot water to OFF but the Megaflo still whirs away.
Conversely if the hot water is ON but the heater is OFF the Megaflo is
totally silent. Does this sound right ??

Aside from that, what is the best way to use the Megaflo - does it switch
itself off when the tank is full or if I left it ON all day would I have a
big bill (like an immersion heater would give if left on permanently) ?
What does the ONCE switch on the EP2002 do in relation to hot water ? (I
know what it does for the boiler).

Many thanks !!

Richard.