Twin element, single stat immerson only heating top of tank

[TheBursar]

I recently installed an immersion heater. It's a twin element, single thermostat type. The thermostat is as short as the short (sink) element. Whether it is set on sink or bath, only the top of the tank gets hot. The bottom goes up a couple of degrees on bath, but that's it.
It is wired correctly and I measured the resistance of the the two elements and they seem to be OK. Any ideas?

 

[steved101]

you should always fit the correct length thermostat for your immersion heater.
that's probably the reason it's not heating fully!

 

[TheBursar]

Thanks, but when the element comes with a thermostat that's only as long as the shorter element there isn't much you can do. Apart from be more careful when buying I suppose.