The message
from Jon contains these words:

Sorry I have come late to this thread and most has already expired so
what I say below may already have been said before.

Should my radiators come on when the hot water comes on - even though
the heating is set to "off" on the programmer, and it's so hot in the
house that turning the stat up to maximum (30) does not cause it to
"click" on?

No it should not. You have a wiring error or a fault with the valve.
Call the installer back if it is a new system.

It's 9 years old (built with the house). The pump was replaced recently
but I visually observed the whole process and he simply did remove the
old pump and refit the new one.

Are you sure that the absence of 'click' with the thermostat is it not
turning on? Given the symptoms it seems more likely that the thermostat
is not turning off. This is easily checked by disconnecting the
thermostat (after isolating the supply).

--
Roger Chapman