E7 meter - Night readings consuming electricity during day - help

Assuming you don't have gas, similar reasoning applies to your immersion heater(s). There may be one at the bottom of the tank on a 7h supply and a top-up one higher up on the 24h supply with a switch marked 'Boost' or whatever. Needless to say, the Boost switch should only be used for a quick top-up if things have gone wrong !

Alternatively, a cheapskate solution may have just one immersion heater on the 24 supply with a local timeswitch. If it's a mechanical one similar to this it's not good news because a power cut can leave you paying peak rates for months if you don't spot it.

A_vasquez26,

If its an E7 / E10 / or E anything spec it should already as stated above be PartL spec, due to the higher than normal storage temperatures the capability of the insulation to preserve the temperature of the water the type of insulation has a very very low standing heat-loss [one kW per day (kWh/24h) on a 125 litre cylinder] permissible thermal transfer rate from the 60mm of insulating foam, modern ones have the additional benefit of recessed immersions and thermostats to reduce even further energy wastage. All dual PartL cylinders have a top up facility [see below] and is usually operated by a standard 60 minute top-up water controller such as the Horstmann unit also shown below. I've never used or needed the 'top up' I've never used the 'boost flap on the NSH

If you do not touch the E15 boost controller and you get a tank of nice hot water every morning its still tele-switching on and off. You have check your online tariff and get 'cheaper rate electricity between 12:30am - 7:30am'. Have you got x2 elements top & bottom{above} both with wiring going somewhere and what is the somewhere they are going to ?




The top element [top-up-day rate] will give a couple of big sinks of hot water when used, the bottom element [E7-night rate] will give a full bath and a couple of sinks of hot water. Heat loss is not linear to the volume of water, the bigger the mass the slower the loss rate, eg [figured below are 'ish' but about right] :

1 kW per day (kWh/24h) on a 125 litre cylinder
1.5 kW per day (kWh/24h) on a 250 litre cylinder
2 kW per day (kWh/24h) on a 300 litre cylinder