Pricing to replace a vented cylinder with an unvented cylinder (megaflo)

[Roy_66]

One silly thought I've had on these conversions. If you only do the hot water and leave the heating, you then end up with a header tank in the loft that will hardly have any flow to it. So a long length of dead stub, which is presumably not a good idea? ( Apologies I'm not sure of all the answera here)

So assume most change both systems to pressurised at the same time.

Cheers,
Roy ( very amateur plumber, no qualifications whatsoever )