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

bpj

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? 

I think the neon is normally connected directly to the load side of the switch - so if the switch was simply wired the wrong way around it would always be on rather than only when the shower is turned on. I can't think of any wiring that could put the neon in series with the shower without short circuiting the switch (but I'm certainly not an expert).

Google does suggest that dodgy neons are not uncommon, and in at least one forum thread someone complains of one that often comes on and off with the shower. Perhaps a bad neon contact could be made and broken when the shower is drawing current by a similar mechanism to the one Jeepers suggests could be causing the intermittent bad connection on the supply. 

While a loose connection certainly seems the most likely explanation, if I'm reading it right the OP needs wait a few minutes and then cycle power to the shower to get it working again. Perhaps this power cycle is just providing a physical jolt to the switch which is reseating a loose cable, but otherwise it does seem suggestive of an over temperature cutoff on the shower itself, which is also consistent with it only happening on the high setting and after a relatively consistent amount of time. Given this less likely theory is very quick to test, it might be sensible to do so before searching for an elusive junction box at least.

Really a lot more hints are needed from the OP though. Here are some questions:

 - Is the flow rate good?
 - Did you replace your shower head / hose when you replaced the shower unit?
 - If you run the shower with the head removed, does it still cut off?
 - Is the neon light normally on when the shower is off?
 - If you cycle power to shower immediately rather than waiting a few minutes, does it work?
 - If rather than turning the shower off and on again at the isolator you just wait, does the shower eventually start working again?
 - If rather than turning the shower off and on again at the isolator you turn it on and off again at the MCB, does the shower start working again?
 - Did your electrician examine the wiring at all?
 - Do you own a multimeter and are you confident in using it? (If so, don't trust that neon light!)

cajef

I had the same problem last year, isolated the mains supply and checked the pull cord switch and found a blackened cable and terminal in the switch, bought a new 45amp pull switch, found enough slack in the cable to pull some through to cut out the overheated end and made sure the connections were really tight, problem solved.

Risteard

It's definitely a loose connection. As an experienced electrical contractor I am stating this categorically. Both the cable and the terminals it is connected to are likely to have been heat damaged (likely in the pull cord) and this will need replaced as will the section of burnt out cable need to be cut back substantially back to bright copper if there is sufficient length, otherwise replaced or appropriately jointed.

bpj

Risteard said:

It's definitely a loose connection. As an experienced electrical contractor I am stating this categorically. Both the cable and the terminals it is connected to are likely to have been heat damaged (likely in the pull cord) and this will need replaced as will the section of burnt out cable need to be cut back substantially back to bright copper if there is sufficient length, otherwise replaced or appropriately jointed.

I'm sure you're right, a bit strange that their (perhaps less experienced) electrical contractor didn't notice though!

Le_Kirk

Risteard said:

It's definitely a loose connection. As an experienced electrical contractor I am stating this categorically. Both the cable and the terminals it is connected to are likely to have been heat damaged (likely in the pull cord) and this will need replaced as will the section of burnt out cable need to be cut back substantially back to bright copper if there is sufficient length, otherwise replaced or appropriately jointed.

Used to get this a lot when I was a service engineer (cured now) because of the guy I worked with called Lew, Lew Snootrals!

fenwick458

bpj said:

Risteard said:

It's definitely a loose connection. As an experienced electrical contractor I am stating this categorically. Both the cable and the terminals it is connected to are likely to have been heat damaged (likely in the pull cord) and this will need replaced as will the section of burnt out cable need to be cut back substantially back to bright copper if there is sufficient length, otherwise replaced or appropriately jointed.

I'm sure you're right, a bit strange that their (perhaps less experienced) electrical contractor didn't notice though!

Its odd yes but the Mira tech would only be interested in the shower, and nothing else. part of the T&C's for booking a Mira tech is to confirm that the electrical supply has been tested up to the shower isolator, or it used to be...
and the independent spark who did a load of checks but didn't actually check the shower pulswitch, he was probably inexperienced...