Mira Zest problem

Boff · Posted: Wed Dec 13, 2006 10:04 pm

Hi I have a Mira Zest 7.5/8.5 kW shower (going off the instruction manual - not sure which one it is sorry, it was already here when I moved in a few years ago.)

It had been working fine up until a few months ago but now if I set it to High the water will go cold after about 5-10 mins of use.

Low and Medium work fine. Also it does seem to cut out sooner if I increase the temp when on High.

I've cleaned & descaled the shower head, opened the mains valve fully outside the house (It was on about 3/4 fully open) but this has had no effect.

I've tried leaving the shower running after it's gone cold but doesn't get hot again unless I turn it off for a bit.

I assumed it was a heater element problem but could it be dodgy wiring or something? The house is pretty old.

Long and short of it is should I replace the shower or is the problem electrical?

Cheers!

Steve · Posted: Wed Dec 13, 2006 10:58 pm

Are there 2 controls? One of these is for the heater control, with 3 settings? Turn this to full - you need it at this time of year.

Then adjust the water flow to get the temperature you desire, using the other dial, which is a variable dial. We have ours at around half-way - it varies every time we use it, as the temperature of the incoming water varies.

I suspect the thermal cut-out is operating, caused by you having the temperature set too high. If it is tripping out when at "normal shower" temperature , there's something wrong.

However, if you're running it at " steam bath, burn my skin red-raw" temperatures, expect it to cut out.

Boff · Posted: Fri Dec 15, 2006 9:49 am

Thanks for the reply, no offence but I know how to work the shower! It's definitely not running too hot as I've had it running fine for the last 4-5 years.

It went again this morning as it happens, but this time it was on Medium.
I checked the switch in the airing cupboard and the light was off, after 10 mins I checked again and it was back on so I'm thinking it's defintely an elctrical fault.

Could it be the switch itself? I'll check the fuse anyway in case it's loose or anything (it's a really old fuseboard with the ceramic fuses you have to put the wire in yourself) but all other electrics are fine so I know the tripswitch isn't being tripped.

Bad connection somewhere maybe?

I'm getting worried now as it's obviously getting worse if it's starting to go on the Medium setting now.

Last thing I want to do is blow the elctrics in the middle of winter!!

systemtek · Posted: Fri Dec 15, 2006 11:28 am

Does the shower have a power LED on it ? If so watch to see if it goes off when you say it goes cold, also is it fed by a pull cord switch with a LED again check that. When you have your shower on is the heating on ? washer on, dishwasher on anyone running water any water that could decrease performance ?

Spark123 · Posted: Fri Dec 15, 2006 6:22 pm

Sounds to me like you are looking for a loose connection or a dodgy switch.

Steve · Posted: Fri Dec 15, 2006 7:56 pm

50p says incoming neutral has burnt out in the switch. This is what it definitely sounds like.

open it up and take a picture please!

ricicle · Posted: Fri Dec 15, 2006 7:58 pm

crafty1289 wrote:

50p says incoming neutral has burnt out in the switch. This is what it definitely sounds like.

open it up and take a picture please!

With the circuit off

Steve · Posted: Fri Dec 15, 2006 8:50 pm

ricicle wrote:

With the circuit off

naturally!

Boff · Posted: Fri Dec 15, 2006 11:54 pm

I'd just come on here to say it was the switch but looks like you lot beat me to it!

I pulled the fuse when I got home from work and opened the switch up, the live on the supply coming in to the switch had burnt bigtime, it had almost burned through to the neutral aswell and melted a bit of the inside of the switch! I took a photo of the switch to send to my mate as it goes, I'll attach it now.

My other mate's a spark so he said he'll pick up a new switch and re-wire it tomorrow afternoon.

s**t hot, I thought it was gonna be time for a new shower - and I get to use it on the High setting again!!

Next question, why did it happen? Moisture? (Doubt it cos it's in the airing cupboard). Dodgy connection? Wrong wire? (Not sure what size it is sorry - seems thicker than normal twin & earth though.) The ciruit's on a 30amp fuse if that makes any difference.

Steve · Posted: Sat Dec 16, 2006 12:57 am

the live melted - unusual!

its normally the neutral - theres a myth its because people dont associate
danger / importance with the neutral wire, so dont tighten it up as much.

Chances are, the screws in the switch just loosened over time - vibration
and heat can cause this, the wires naturally get hot when you have a
shower.

The wire looks like 10mm², but hard to tell. Definitely 6mm²+ anyway.

Boff · Posted: Sat Dec 16, 2006 12:45 pm

Ok thanks - sorry for the big pic forgot to resize it!

My mate's calling round later so hopefully he'll get it sorted before I start to smell!

Was a bit worried there was some underlying problem that had caused this.

Well whenever I'm messing about with wiring I always make sure they're ALL done up tight regardless of colour!

Thank again for the help

Steve · Posted: Sat Dec 16, 2006 12:59 pm

Boff wrote:

Well whenever I'm messing about with wiring I always make sure they're ALL done up tight regardless of colour!

Its a subconscious thing, unless you really think about it, the brain associates less importance with the neutral and earth wires!

There shouldn't be any other problems on this circuit, and as long as theres some slack on those cables, it shouldn't be a problem to cut back and re-terminate.