Immersion Heater boiling the water

[I think this kind of thread goes here]

Hey guys,

I live in an apartment where we have the cold water tank located above the hot water tank which is heated electrically and automatically every morning. For most part, it does its job of automatically switching off when the water reaches certain temperature or the switch-off time has passed in its internal configs.

Although lately I have been have a bit of problem with the heater: on some days the internal thermostat wouldn't kick in and can cause the water inside to boil (which would splash the water through the pressure-relieve pipe violently into the cold water tank - splashing water everywhere in storage area where the tanks are located)

It doesn't always happen - last couple times it would go for 9, 10 months without incident; and then i would have 3, 4 overheating days in a week.


Something I should be concerned about?



PPS: when I shut off the water heater manually i can sometimes see a blue spark inside the terminal the instant the switch has been flicked - although I think this is a normal electrical spark caused by when the switch has been tripped while the current is still active?