Forgive me, but im new to this forum and know pretty much nothing about central heating and hot water systems! I moved into a rented semi with my girlfriend a couple of months ago, and in our bedroom we have two doors, one of which contains the immersion and timer (the boiler is in the kitchen). However, we have noticed that when we turn our heating or water system on, there is a pretty loud rumbling/whirring noise behind the other door in the bedroom (which we cannot open). I as wondering if you guys knew what this is? Ive lived in a few houses in the past and none of those systems have made this noise, which is loud enough that we cant set the timer to come at night as it would wake us up. Once again, my apologies if this is a basic question to which there is an abvious answer. Many thanks in advance.
Sounds as though the pump for the heating system may me located behind this closed door. Any air mixed in the system water passing through the pump will result in a variation of noises as described in your post.