Economy 7 Immersion Heater Controls
Properties with an Economy 7 electrical supply will have an Economy 7 capable electricity meter which will turn on and off a 2nd (generally smaller) consumer unit (or the e7 side of a combined consumer unit), the economy 7 electricity meter is owned and controlled by your electricity supplier.
The economy 7 on/off times are set by your electricity supplier, the 2nd consumer unit (which is controlled by the economy 7 electrical supply) will in-turn supply the off-peak immersion heater and any economy 7 storage heaters.
Your electricity supplier will turn on the Economy 7 electrical supply to the 2nd consumer unit during the off-peak (cheaper rate) hours, this will in-turn, turn on the off-peak immersion heater to heat the water inside the hot water tank until it reaches its desired temperature, when the desired temperature has been reached the immersion heater thermostat will click-off and the immersion heater element will stop heating the water any further.
To clarify, when the water reaches the temperature as set on the immersion heater thermostat, the thermostat will interrupt (turn off) the electrical supply the immersion heating element, therefore at this point it will not be consuming any electricity.
When the water inside the hot water cylinder has reached its desired temperature and has stopped heating the hot water, while there will still be power to the Immersion heater during this off-peak period, it wont actually be “consuming” any power as the stat has shut-off the electrical supply to the actual heating element.
If the water cools below the immersion heater thermostat setpoint (during the off-peak hours) then the thermostat will activate and start reheating the water, this is why it is important to ensure your hot water tank and associated pipework are well insulated in-order to minimise heat loss.
Fitting a hot water cylinder jacket to your hot water cylinder will help to reduce heat loss from the cylinder, while fitting pipe insulation to the associated pipework will reduce the heat loss from the actual pipework.
Your electricity supplier will turn off the economy 7 electrical supply when the off-peak rate ends thus turning off the power to the economy 7 (off peak) immersion heater and e7 storage heaters.