I have a copper hot water cylinder that was providing hot water in the morning via a timer on an E7 switch. This has stopped working though the boost is working fine. As it was a gradual decline in temp before complete failure I read around and it looked like the element used for the cheap rate overnight supply might have failed.
I drained the tank and got the immersion heater out with a view to replacing it as it was only cheap. However, I discovered that there is a single immersion heater which turned out to be a dual element twin thermostat immersion heater made by Heatrae Sadia. I rang them and they said they no longer make them. I went to a couple of plumbers merchants and neither had even seen a heater like the one I have and both were not 100% sure about being able to replace it with a single element heater.
The heater is 15+ years old so not being able to source the same one is fine but I am left wondering what (if anything) I can now do to be able to get both the overnight E7 heater coming on and the boost. Is this possible with a single element heater? Are dual element heaters still available? After lots of research I still cannot work out how the heater 'knew' which element to use for the overnight/boost given there was single power supply feeding it from the switch.
