The red light on my pull cord electric shower no longer comes on, hence it doesn't work. However, there was a brief period yesterday where it worked suggesting it's an electric fault and can be fixed? There's a great article explaining how electric showers work and if someone could at least point me in the right direction that would be great.
I've never seen an electric shower (looks to be a European thing?) but based on the diagram in that article you've got electrical contacts near moisture. Corrosion is quite likely and would cause intermittent problems like you describe. Turn off all power to the device then open it and check for "crud" on any of the electrical terminals. a fine brass-bristle brush can help remove it, or even a Scotch-Brite scrubbing pad.
As discussed in the comments above, I removed all crud & corrosion, so by process of elimination I am hopefully getting closer to an answer which is contained in this very elaborate detailed response; check it out