New intermittent airlock in bathroom cold water, no recent changes on system

[rebelbuttmunch]

Hi
There's been no changes in a few years on the system.
The issues is that intermittently the cold feed from the attic stops flowing. No cold water in bathroom taps/showers/loo/downstairs loo/taps.
Hot water is fine. I can't really tell if the immersion tank is being fed all the time, but there is never any pressure drop from the hot taps.
Mains water is fine.
Attic Tank seems to always have plenty of water and is well fed.

I've tried to put the bathroom mixer tap on 50/50 mode, cover it with my hand, then jiggle the shower mixer tap on/off. After a bit of random jiggling it can sometimes start a bit of a splutter and then works again. I've to repeat this a few times to get it flowing.

I've a stuart turner monsoon pump inbetween the tank and the taps/loo and this problem only happens with the pump is turned off. I'm wondering if there might be a small blockage in it that's enough to hinder the gravity fed system, but then maybe my jiggling fix shouldnt ever work...
One thing I've noticed is that the upstairs loo seems to be quite slow to fill, I wonder if it's eventually letting air back into the system.

I'm going to try and poke around the upstairs loo feed and see what's happening there. It's all behind a tiled box though and its a push button flush. Edit: Seems like a simple investigation to rule out the loo

Any ideas appreciated!

 

[rebelbuttmunch]

I took apart the cistern, it was handy enough. It turned out that this helped because there's hot water being fed in there when the pump is switched off. I think now that there is a problem with the pump, some kind of return valve or mix problem. I'll have to call out a plumber for a look