How much water do I really need to change ?

[itiwhetu]

What has this got to do with this post.

 

[AilyNC]

What has this got to do with this post.

OP said he thought his hot tap was ok to use but wasn't certain. I'm just confirming that it is in fact safe to use as his hot water comes from mains to boiler to tap and doesn't sit in the storage tank.