Water Heater Instructions – using the Horstmann E7 Immersion Timer Switch

Do you know how to use an E7 timer for heating water properly and reduce your electricity bill?

Water timer

The water timer is the 24 hour clock on the panel. This has 2 settings as seen below, summer and winter. Firstly, make sure and set the 24 hour clock to the correct time of the day. Then set to summer / winter depending on the time of the year.

After you have set your timer you must turn the switch on the panel to timed. Once this is set to timed you must leave it in this position going forward. The only time when this should be off is if you are going on holidays or if you don’t use hot water.

By setting the timer correctly, the program built into the timer will then heat a full cylinder of water from the hours of 4am to 8am using the economy night-saver rate, thus reducing costs.

There are thermostats in the cylinder designed to stop the water overheating. It turns off the immersions once the cylinder has reached the correct temperature.

Boost Switch

Everything is going great, you have your shower set up on timed, you have hot water in the mornings, but let’s say you wanted another shower in the evening and there was no hot water left. You do not change the timer!! To get hot water in the evening, instead you will see a button with boost on it.

This boost will only heat half a tank of water at any one time. The button twists clockwise and will turn your immersion on. The numbers around this button are the desired minutes for which how long you want to have the immersion on for. The Boost can be on for a maximum of 2 hours at a time. It turns itself off automatically as it is a timer which counts down anti clockwise.


As people typically use it in the evenings, it consumes daytime electricity, which, if used regularly, can significantly impact the household’s electricity bill. Knowing how to use an E7 timer for heating water properly will guarantee your hot water on time and contribute to your electricity bill.