Should "Water Heater" switch be on?

Hi, I've been having problems with my Pulsacoil 2000.

It heats up water every night using the Off Peak electricity, but how much hot water you get the next day is variable - some days it can be as little as half a shower before it goes cold. The boost button also works and this is what I tend to use when the water runs out. So both off-peak and on-peak immersion heaters work.

The off-peak and boost both work from a clock timer which works fine. Below the clock timer is a switch labelled "Water Heater" which I always keep off. When you switch it on, the Pulsacoil starts making kettle noises (similar when I use the boost button). I always keep it off because I believed that this would heat the water all the time (although I did wonder why there was a boost button as well as this separate switch)

Below the Water Heater switch is another power switch which is always on.

I recently spoke to a neighbour who keeps their "Water Heater" switch on all the time. I am now wondering whether this switch is a Pump Switch and it should always be kept on and this is what is wrong?

(The LED flashes two times a second which seems normal)

Thanks very much for any advice!

yep.

Thanks, I'll make sure I keep it on in future. I'm just surprised it was producing hot water at all with the switch off!