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Missing Fuse For Electric Shower That Won't Heat Up?

Postby jkphilips40 » Mon Aug 18, 2014 12:03 pm


I have an electric shower that is not heating up and I think its because the fuse is missing from fuse board for it but it is an old fuse and dont know where I can get a replacement or what kw the fuse should be. The other fuse's are wylex.

I have photots but wont let me upload I think it needs to be orange as the other seems to be colour matched. Not sure if there is a problem with electrics or not but if I can get a fuse to test it first

Any suggestions appreciated


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Postby TheDoctor4 » Mon Aug 18, 2014 4:33 pm

Hi Stephen

If you are having issues in uploading images there is some information on how to do this here:


Hope this helps

Kind Regards
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Postby ericmark » Tue Aug 19, 2014 10:42 am

The old Wylex box had four different devices which could be used. At first it was a re-wirable fuse using standard fuse wire, then the cartridge fuse holder replaced these I think it needed base swapping and then a push button MCB and finally a switch type MCB the WYLEX 40A SP Type B Curve MCB Product Code: 77992 is still made "screwfix number" the fuses in screwfix are only up to 35A can't see any fuse holders sold.

In theroy before swapping from fuse to MCB you should test the earth loop impedance the MCB is in fact two devices in one the thermal trip is slow acting and the magnetic trip is fast acting but needs 5 times the current of the thermal trip and that's why measuring earth loop impedance is important. Unlike a fuse where if slightly over it takes slightly longer with the MCB slightly over takes a lot longer to trip.

Showers come in two major types the power shower uses very little power and likely would need a 6A MCB but the instant heat type uses a lot more current and either a 32A or 40A MCB.

There are 3 cable sizes which could be used 4mm sq, 6mm sq, and 10mm sq some times you can see size written on the cable but hard to work out from just looking at the cable. Also cable current carrying capacity is also controlled by how it is fitted and fitting a 40A MCB with 4mm cable could allow the cable to overheat.

Reading the size of the shower you may know how much it needs but often showers have fuses or MCB's below the size they really need with the idea we do not use them for long so fitting a 40A MCB without knowing what size the cable is could cause overheating will prolonged use or fault.

Since the fuse is missing fault is a very real possibility.

With the idea it could be a DIY fit also possible the RCD protection is missing.

Assuming a RCD is fitted and it is an instant heat type fitting a 32A MCB is unlikely to cause a problem but at £10 each I would say getting it tested first may be the better idea.

If you do change to a MCB yourself be aware when the base screw is removed it exposes live parts so main isolator needs to be off and also the fuse cover will no longer fit.

I strongly recommend you get an electrician to do this for you and test it before trying to fit the MCB. Likely the fuse was removed because there is a fault and just replacing could be dangerous.
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Postby ericmark » Tue Aug 19, 2014 12:43 pm

I have just seen the photos you put up on DIYnot electrics and I see no RCD which means even it is for the shower you need more than simply a new fuse.

Also since red and from age it would have been 30A you should not use one any bigger. It also shows re-wireable fuse carriers these have been outlawed for ordinary persons to use because it is too easy to replace with wrong size wire today has to be cartridge or MCB type.

It looks as if the base for the missing fuse has already been changed for a cartridge type fuse which is why the other 30 amp fuses will not fit.
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