Immersion heater element problems

[pblues1]

Hi,

I have an approx 200 litre tank with a 3KW immersion heater element linked up to economy 7 and a similar on demand immersion heater higher up the tank.

A couple of years ago the economy 7 element broke so we got a plumber to replace. It broke again 10 days later. I then replaced the element myself more recently but again after about 10 days it stopped working.

The on demand heater works fine but i cant understand why the element keeps breaking. Any ideas would be gratefully received. The tank is quite old but works fine otherwise!

Thanks...

 

[simond]

The Eco7 element is the one near the bottom of the cylinder.

Years of limescale deposition gradually fills the bottom of the cylinder up.

If there is any of the limescale pile in the base of the cylinder touching the element, it will locally overheat and short circuit.

This is the only likely scenario given the number of units you have got through.

Shifting the scale can be difficult, it is really a cylinder out job and you may as well replace the entire thing in this case.