Low cold water pressure upstairs

[SmallTalk]

I seem to have a problem with low cold water pressure in my upstairs bathroom. The cold taps on the sink and bath are fine, the toilet cistern is slow to fill and my electric shower is showing a low pressure indicator.
The cold water tank is in the top of the airing cupboard in the bathroom.
We recently had a new kitchen sink put in but the system wasn't drained and the water supply to the sink was turned off using the isolation valve.
I'm wondering if there could be air in the system and if this is the case how to I clear it?

 

[Madrab]

If the bathroom has been piped and supplied correctly then the shower will be on the mains, chances are if the toilet is now slow filling then that will be on the main too. The others are cistern fed therefore not affected.

Check the mains stop tap has been opened fully. If this has happened at exactly the same time as the work was done, see if you can get them back in to check.