Thanks Armo74 & TCCHeating for your helpful answers.
I'll try to upload some photos in the coming days but I've got a busy week ahead of me.
The installer(s) made some basic mistakes, which have been corrected and the 1-day job stretched to 4 days - two of those days I was left without...
I've just had a new boiler installed to replace a worn out unit. During the installation the engineer added TRVs to most of my radiators.
A new pump was installed directly above the new boiler connected to its outlet. This pump is connected the right way round but the water seems to flow...