Ah, Chester, loved Chester! Been there on my way to Wales, I wanted to see it because of it's history with the Romans :)

Doesn't have to be anything as old as the Romans.. Could have to do with someone that used to live there.. Difficult to tell from a distance..
Normally you can send entities away, as long as you don't get angry, but you gotta be and feel strong and adamant about it.
But not sure if an entity that slams doors will bugger off just like that :/
More likely he wants you to leave ... If it becomes too much, get someone in ..

yes the door slamming got to me to be honest, glad to read it won't leave easily, how reassuring lmao
if it carries on or gets worse i'll get a priest or someone.

Glad to have been of service, lol. No seriously .. just told you so you don't start sodding round with it unless you do know what you're doing ..
Now I don't have a network in the UK, not really, but if you want some help, or simply someone to 'check it out' (which can be done over distance), you could get in touch with Sally Morningstar. She lives in or near Glastonbury ... Google her if you want... easy to find.
I trained with her for nearly two years, she's pretty danged good and I think she can at least give you advice on what's going on.