I'm using Alpha with auto earth circuit check indicator. Green light means the earth circuit is fine. Red light means the earth circuit is not ok. If earth circuit is not ok, the heater is still working but if there is any circuit leakage, your RCCB wouldn't trip and it may lead to electrocution or fire.

Ask your electrician to check your Joven earth circuit first then check the earth circuit of the entire house.
Meanwhile, DO NOT USE any water heater in your house until you find out the problem.

Add on:
Have you done the ELCB test on the water heater yet ? Does it trip?
Also, please do a trip test at the RCCB in the main DB.

This post has been edited by aeiou228: Nov 24 2015, 07:44 AM

Press the test button. No trips means your water heater is not earth. Very high risk if you continue using it, once leaked, no protection from electrocution at all. Check your green earth wire in the heater and wall socket, make sure it is securely fasten then press test button again. If it trips, that means you have EELS protection.

if earth wiring no problem, press test button at your RCCB to check the entire house earth circuit. Water heater can be faulty too that's why you need to trouble shoot one by one to find out the root cause.