Electric shower cutting out after 4mins - cannot diagnose problem!!

Billy_B_North

Apodemus said:

Have you looked at the water pressure?  Sounds like it copes with a certain amount of heating then goes to an overheat lock-out, which re-sets once it cools down.  If all the electrics are OK and it is occurring on multiple identical machines, then it may be that the water pressure is marginally too low?  I presume it is fed directly from the mains, rather than from a header tank?

EDIT:  I see that it only happens on High, which is what you would expect if it was an overheat cut-out issue.

I’d be looking at the water pressure and / or flow rate too. Does the head need de-scaling, or had mains pressure dropped? It sounds as though there’s not enough water passing through so it’s tripping the fail-safe.
Electric showers really can be a pain, is there any way that you can install one that runs from your hot water supply instead?

coffeehound

Billy_B_North said:

I’d be looking at the water pressure and / or flow rate too. Does the head need de-scaling, or had mains pressure dropped? It sounds as though there’s not enough water passing through so it’s tripping the fail-safe.
Electric showers really can be a pain, is there any way that you can install one that runs from your hot water supply instead?

Anything happening in the shower itself would not affect the neon in the celing switch. 

Jeepers_Creepers

Lawdie!

When the shower goes off, so does the neon light on the pull cord switch! Or, to put it the correct way around, when the light on the pull cord switch goes off, so does the shower.

There is nothing to suggest the shower is at fault. Or the water supply.

There is everything to indicate that it's due to a fault in the leccy supply betwixt the CU and the pull cord switch.

First check the switch. Then check the MCB. Then check the cable in between.

Le_Kirk

Jeepers_Creepers said:

The evidence here points directly at an electrical supply fault as Risteard says.

The fact that the indicator light in the pull switch goes off shows that the power has stopped before it reaches that light. 

This could also indicate that the switch is faulty as the indicator would be shining/lit when the switch is ON and not shining when the switch is OFF.  It could also be OFF for a supply failure or a loose connection as @Risteard writes or a faulty contact within the switch.  This is why I suggested investigation of the switch would be my (first) next step.

Apodemus

Jeepers_Creepers said:

Lawdie!

When the shower goes off, so does the neon light on the pull cord switch! Or, to put it the correct way around, when the light on the pull cord switch goes off, so does the shower.

There is nothing to suggest the shower is at fault. Or the water supply.

There is everything to indicate that it's due to a fault in the leccy supply betwixt the CU and the pull cord switch.

First check the switch. Then check the MCB. Then check the cable in between.

Jeepers,  I agree with most of what you say, but it is surely unusual for a wiring fault to be as predictable as the OP describes and it doesn't really answer for the fact that it only happens when the shower is at the high setting (although I guess this could be a thermal issue that varies with the power being drawn).    I wonder if the switch is wired wrongly, so that the LED indicator is not on the live side of the switch, only showing as "on" when the shower unit is actually drawing power.  When the overheat cut-out puts the shower into a safe-mode, that power draw ceases and the indicator light goes out. 

I know that my scenario postulates two faults, when a single fault is always the most logical conclusion, but this is a strange one!

Jeepers_Creepers

Apodemus said:

Jeepers,  I agree with most of what you say, but it is surely unusual for a wiring fault to be as predictable as the OP describes and it doesn't really answer for the fact that it only happens when the shower is at the high setting (although I guess this could be a thermal issue that varies with the power being drawn).    I wonder if the switch is wired wrongly, so that the LED indicator is not on the live side of the switch, only showing as "on" when the shower unit is actually drawing power.  When the overheat cut-out puts the shower into a safe-mode, that power draw ceases and the indicator light goes out. 

I know that my scenario postulates two faults, when a single fault is always the most logical conclusion, but this is a strange one!

Yes, it's a strange one, and the '4 minute' issue is what seems to make it particularly strange. I suspect that's a red heron tho' (sorry, old forum joke).

I doubt this always takes '4' minutes, but it just happens to take a 'while' for the wire contact to heat up and go 'high resistance' - when the OP is ~half-way through their shower, for example.

The bottom line is, it doesn't matter in this case which way the pull switch is wired (and plenty have been connected back-to-front); what does matter is that, if the light in the switch goes off when the shower goes ditto, it's then an issue with the supply of power to the shower (in fact a power supply issue that goes no further than the switch). So it has nothing to do with a fault in the shower itself or the water supply. 

Yes, it seemingly happens on the shower's 'high' setting, but that's no surprise as that's when it's pulling the full 9kW, so no great wonder that's when the bad connection goes 'high'. Good chance if the OP ran their shower on 'min' - around 4kW - they could have a loooong shower (and that poor connection would 'only' become hot...)

Apodemus

Am I wrong, then, in thinking that if the pull-cord switch was wired so that the indicator LED was on the neutral side rather than the live, it would only be on when the shower was actually connected and not go off when the shower's fail-safe wiring disconnected it? 

Le_Kirk

@Ell_ma has the switch actually been tested yet?

Jeepers_Creepers

Le_Kirk said:

@Ell_ma has the switch actually been tested yet?

They've had Mira and sparkies round, but I suspect not!

Jeepers_Creepers

Apodemus said:

Am I wrong, then, in thinking that if the pull-cord switch was wired so that the indicator LED was on the neutral side rather than the live, it would only be on when the shower was actually connected and not go off when the shower's fail-safe wiring disconnected it? 

Just for clarification, the two sides of the switch are 'supply' (live) and 'load' (what you call 'neutral'?). The red neon is wired across the 'load' side so it should only come on when the switch itself is 'on'.

If the switch is wired t'other way around, then the red light will be on all the time, regardless of switch position.

I presume this switch is wired correctly since the OP seems to suggest it comes on as normal only when the cord is pulled. Then it goes off when the shower goes off due to the fault.

What we can say with (I think 100%) certainty, then, is that the power has stopped before it's reached that neon light. That obviously means it ain't going any further, so the shower certainly won't be getting any.

The CU itself works - the OP has working lights and sockets and stuff.

Sooo, the fault is either in the MCB supplying the shower (ie where it's tightened onto the busbar, or where the shower cable goes into it, or even within the MCB itself), or in the supplying cable (very unlikely - unless there's a JB somewhere along its length), or in the pull switch (either the supply terminals not making good contact with the supply cable, or else within the switch itself.)

It's unlikely to be the 'load' terminals since the neon light is wired separately to these, even tho' ultimately to the same side of the circuit.