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The electrical voltage I'm using is 240v similar to Britain's kind and the electric switch connected to it has been broken before probably a year ago. Previously, the light indicator(switch) was a half dimmer than usual and the heater wouldn't work until i smack on the switch a couple of time then the light brightens up before i could use. I changed the whole switch and it worked until recently, same thing happened to the light indicator of the switch dims again and no matter how i smack it, turn on and off, it wouldn't work.

I'm wondering if there's something wrong with the whole system inclusive of the water heater itself or could it be the electric wires behind the socket etc? Should I just get another switch and try again and what if it doesn't work?

Additionally, I wish to know if I could use a test pen on certain parts to test if electric is passing through? I worry I might get electrocuted.

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Thanks in advance!

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Too much current for switch (probably - so check it)

Previously, the light indicator(switch) was a half dimmer

The neon indicators don't last forever, they are not essential to the working of the switch.

same thing happened ... no matter how i smack it, turn on and off, it wouldn't work

I think that switch is not rated for the current it is passing. It may be only rated for 20A. Passing a higher current can cause the contacts to burn out over time due to arcing.

An electric shower is usually on a 32A circuit in older houses or on a 40A circuit in newer houses.

A 9 kW shower at 240V uses 9000/240 amps = 37.5A.

You need to install a dual-pole 45A switch designed for use with an electric shower. These kinds of switches are sometimes physically larger than the "20ax" switch you show. 20ax suggests 20A only. It isn't capable of handling the current and is just waiting to set fire to your home.

I wish to know if I could use a test pen on certain parts to test if electric is passing through?

Most non-contact testers test for voltage only, not current.

However, testing for voltage is probably sufficient.

If there is a voltage drop across the switch, when on, it would indicate that the contacts are burned or pitted, or that you didn't tighten the wire connections enough. The switch would also get warm or hot.

To measure current you would need a clamp-meter around one of the individual wires connected to the switch (not round the whole cable)

Take extreme care when testing this, it is lethal.

See When doing electrical work, what do I use to check wires are safe?

Bottom Line

Replace that switch with a 45A dual-pole switch. If possible, make sure it isolates both live AND neutral.

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