Hey Dave

By which programmer though? the programmer underneath the boiler OR the
7 day immersion heater one? or both?
The boiler programmer (CH & HW).
kiichi ok - so if the boiler programmer controls the valve, what
exactly is the "7 day immersion heater timer programmer" used for?
to heat up the cylinder??

Normally, only if the gas central heating fails.

Kiichi
OK - so if there is no wire connected to the cylinder from the "7 day
immersion heater timer", what is it doing?
it is only a backup if there is a wire coming from the programmer to
the immersion heater, correct?

but i am sure there is only a cable coming from the 7 day immersion
heater timer to the boiler programmer - so how can that heat up the
cylinder when/if the boiler is out?
[...]

2) the 7 day immersion heater timer controls when to heat up water in
the cylinder tank - so that the water in there can be used to heat up
the CH

No. An immersion only heats the hot water - not
the CH.

kiichi
i'm a bit confused now - i thought the water in the cylinder gets used
for central heating (by circulating ho****er from the cylinder to the
radiators) ?

i thought the water in the cylinder was ONLY for central heating? and
the ho****er for taps in kitchen etc gets hot by the boiler which is
heating up waters from main or tank in atic?

so from above, am i right in thinking that both timers settings needs
to be the same?? why not have just 1 controller to do both??

Because the immersion is only a standby in case the boiler is out of
action.
And it only heats the water.

kiichi
so my boiler is heating up both the hot water for my shower/kitchen etc
AS WELL AS the hot water for the central heating radiators?

sorry for all these fundamental questions...
kiichi