I accidentally mended my electric shower. For the last month my morning showers have been spent jumping mostly to the other end of the bath, shivering, whilst the shower intermittently lost water pressure and turned icy cold then went warm again. I planned ringing the plumber today to come out and replace it. Yesterday, not looking forward to my Monday morning cold shower I decided to have a bath in the evening instead. Turned on the bath's hot tap and it barely moved and no water came out so I force-turned it a bit until water started trickling and as it warmed up I was able to open the tap further. Anyway, I turned the tap off again and got the shower head down to rinse the bath out before I filled it and it had full water pressure. So it must have just been an airlock in the water pipe.
My shower this morning was lovely and warm.