Thanks for the reply. Looking at the manual for my boiler (Ideal isar), it shows an inbuilt expansion vessel. Presumably this serves both the CH and DHW??
I have recently bought a Triton thermostatic bath/shower mixer to replace my existing bath taps; I intend to run this off my combi boiler. The blurb that came with the mixer says that an expansion vessel should be fitted to avoid damage to the mixer unit.
What does the expansion vessel do...