Possible causes of electric shower not being hot

[Ramekin]

I have a Gainsborough 9.5kW SDL electric shower, which no longer produces hot water.

The manual says the causes might be too much flow or no power getting to the shower. It can't be the flow since it's a trickle on the highest setting (and quite powerful on the lowest). I know there's ac at the shower (although I don't know the voltage).

Are there any other likely causes?

 

[securespark]

How do you know there's "ac" at the shower?

 

[Ramekin]

Sorry, should have been more explicit. I have a "volt stick" that glows when it's near ac. I used it to check the cable coming from the circuit breaker, the pull switch on the ceiling and the terminals on the shower. It confirmed that ac at at least some voltage level is present.

I don't however have a decent voltmeter to measure exactly what's there.

 

[securespark]

You need to ascertain exactly what you have at the shower.

A cheap multimeter should suffice.

As some have said here, you wouldn't attempt joinery without the correct tools, so why attempt electrical work without the same?