timer for economy 7 immersion heater?

[EFLImpudence]

There are 2 elements, bottom is E7 and top is permanent.

Right.

I was basically looking to avoid having the E7 element boiling on and off through the night for the sake of wasted energy and giving the element longer life.

Well, it will not 'boil'; it will get to whatever temperature you set, then switch off.
Presumably the tank is well insulated and unlikely to cool significantly.
So, as Simon has pointed out you do not really need a timer.
If you think the water is too hot in the morning, turn down the thermostat.
If you do not want a tankful, switch off the E7 and boil a kettle.

From my understanding the suggested time controller would be fed by both E7 and permanent supply spurs. The E7 would then be on the 24 hr time control and the permanent / booster would have the ability to manually switch on with the choice of staying on for 30/60/120 mins.

Yes, but the E7 only has power for 7 hours and once to temperature will be switched off.

 

[tomssi]

So would you say these timers are a waste of money, no real benefit?

 

[SimonH2]

If your tank is lagged then yes, I'd say they have little benefit. If your tank is losing so much heat that delaying turn on of the heater for a few hours will save anything, then I'd suggest you money would be better spent on some good lagging.
If your water is too hot, then just adjust the thermostat - that's free !

Just remember that ideally you want to store all the heat you need for the following day during the night time off-peak period. The off-peak heater is at the bottom of the tank so it can heat the whole tank.
There is some tradeoff. If you heat the tank hotter, then your effective capacity is higher - because you'll use less hot water for a given result. Eg, suppose you want your shower at 40˚, the mains is at 10˚, and you heat the tank to 70˚ - your shower mixer will mix equal amounts of hot and cold to get your 40˚, and the apparent capacity of hot water supply is roughly twice the size of the tank. If you only heated the tank to (say) 55˚, then you would need two parts of hot water to one part of cold to get the same shower temperature and your apparent hot water capacity is reduced to only 150% of the tank size - a reduction of 25%.

Against setting the tank hotter ... the standing losses (ie how much heat it loses through its insulation) are higher, and people may just use the same amount of hot water (eg just wash up in a hotter bowl). The standing losses aren't normally wasted - they contribute to heating the house as long as the tank is in an internal space and you haven't got windows open to cool down in summer.

 

[pretzelz]

Hello,

In response to how did this situation go, 2 years back, I bought a digitial timer, think it was the £15 one off ebay. But I was out of the house at the time the electrician visited to hook it up, and the lodger said he couldn't find the new timer (annoying: it was right next to the electric fuse box in the house deliberately waiting - as told) and so the electrician installation a crusty old second hand dial timer, which granted, seems to have done the job. (and I paid £30 for this).

So, the timer gets a permanent supply of energy from the mains, and turns on and off for a few hours each night, about 2-4am. This does the trick.

I have two readings on my electric meter for day and night, but nothing else to distinguish between them in the house, such as different plug sockets or whatever.

Good luck!

 

[SimonH2]

It's possible that whoever had the E7 meter installed didn't bother doing it properly. But normally there will be an extra wire out of the meter that can be used to feed off-peak loads - and that's switched automatically for you by the meter.
The advantage of using such an output is that you don't have to worry about keeping your local timer(s) in sync with when you get your off-peak. Interestingly, at work (where we're on radio teleswitches) we sometimes find our off-peak turned on during the day - always wondered if it was a "hiccup" in the system, or if they were deliberately adding load as part of system management.