The original post: /r/diy by /u/underpin487 on 2024-11-12 21:53:37.

I have an immersion heater, it has two switches and a timer (the usual from what I am seeing online).

What I am failing to understand is why there is a 4th switch panel that is just a fuse switch.

For context, the immersion heater switches are set up as follows in a 2x2 square shape:

on peak switch off peak switch fuse switch timer

I am unclear what the bottom left switch with the fuse does. With it switched off, the heating elements still heat everything (I can physically hear it doing so) whether by turning the on peak or off peak switches on.

I am confused what the fuse switch does

I am having issues getting hot water for showers at the moment. I have the timer set for 1 hour each evening, it doesn’t seem to be producing enough hot water. But then after literally 5 seconds of having the on peak element on, I have enough hot water for a 20 minute shower. This doesn’t seem right at all, and I’m confused if perhaps the bottom left fuse switch is required to be on for the hot water to be moved from the tank?