Circuit breaker has tripped

[Deckkie]

I found that the circuit breaker had tripped on the downstairs lighting circuit after a light didn’t turn on. I don’t know what caused it but I found the the water heater breaker had also tripped (I assume is the water tank heater in the airing cupboard). I could reset the water heater but the lighting won’t reset. There is no evidence of any leakage from the water tank that might have caused the problem, all the downstairs lights are turned off but the circuit breaker still won’t reset. All other circuit breakers are ok.
Any ideas or advise please?

 

[brianmoooore]

What do you mean by "circuit breaker"? MCB, RCBO or RCD?

 

[westward10]

Can you show a picture of your consumer unit so we can establish what type of device has tripped.

 

[Deckkie]

It’s a Wylex unit, here’s a photo (looks like the water heater has tripped again though we never turn it on).

 

[westward10]

Does the lighting one actually go on or not.

 

[Deckkie]

The lighting one doesn’t reset, if you try to it just crackles and goes off again.

 

[westward10]

When you say crackle is it more extreme than that.

 

[Deckkie]

It’s just a crackle as I don’t try to force it on all the way, just enough to tell that it’s not going to stay turned on. I don’t want to risk burning out any wiring.

 

[brianmoooore]

You can't hold it on against a fault - the lever will disconnect from the internal mechanism, but the sound you describe does sound like the noise a MCB makes just before it trips on overload.

 

[Deckkie]

Yes so if it’s tripping with all the lights turned off at the switches it points to something on the internal wiring (rather than something like a blown bulb that’s still shorting out). I can’t imagine what fault on the internal wiring could come on with it just sitting there undisturbed. Maybe something to do with the water heater but I can’t imagine what, there don’t appear to be any leaks. The water heater breaker still resets ok.