Mira Srint 9.5 Tripping out

[Apneajoe]

Good morning all sorry for the 'URGENT' request however it is
Anyway We have a Mira Sprint 9.5kw, was working perfectly, aside from occasional low flow issues which were always solved by clearing out the internal filter.
Anyway I digress, the shower is currently tripping the fuse when ever the top dial (power?) is turned from the lowest setting (three settings, hollow water drop, signle filled drop and two filled drops) Works fine on the hollow drop setting but this just allows water to flow through no heat, switch to any of the others and pop, everything on the shower circuit trips out. Makes no difference where the temp dial is set to.
Have had a quick nose. Checked the solenoid and I am reading 4(ish) Kohms (Analogue meter set to x1K Ohms) Also stuck the meter across the temp cut off thing on top of the tank and read 0 ohms so assume thats fine as well? Power switch works fine, full power coming into unit etc.
Any ideas on what to check or likely diagnosis? Need to get someway to sorting as I am meant to be leaving on a course today for a week and dont want to leave the other half and little one without at least some idea on the shower.
All help GREATLY appreciated so thanks in advance.
Joe

 

[bernardgreen]

What exactly trips ? Is the the MCB or the RCD ? The RCD has a test button on it and probably twice the width of the MCB.

If the RCD is tripping then there is a earth fault in the shower, most probably in the heater tank and if so this will need replacing,

Measure the resistance between the terminals on the heater and the earth connection ( WITH POWER OFF ) It it is less than 1 meg ohm (1000 Kohms ) then the heater is the most likely cause of the tripping.

 

[Apneajoe]

Hi thanks for the response,
Its the RCD (twice the width of the others in the cupboard and has a small button/light top left)
I will go test the earths now and report back, thanks.
Joe

 

[Apneajoe]

Hi again,
I am getting a reading of about 7 from all 4 terminals to earth on the same setting (x1k Ohms) so assume thats 7000 ohms and therefore too low and the likely cause?
I read 0 between the temp cut off and earth as well?
Thanks

 

[bernardgreen]

That does sound like a faulty tank / heater. It might be something else ( the soleniod for example ) so to verify it is the tank remove the leads from the tank ( make a clear note of how they were connected ) and re-check between terminals and the metal case of the tank ( or its earth terminal ).

 

[Apneajoe]

Thanks for the help, I am pleased to report the problem is now solved... and you were correct to a fashion lol.
I checked the resistance as directed in your original reply, then again with leads off and got same readings although I noticed while rotating the tank to get at the contacts I could make the readings change.. mmmm interesting, soon found if i tilted it a different direction I got much better readings and was created with a slight dampness at one of the contacts.
Half hour on the radiator and all was well in the world again, quick inspect of the casing and directly above the tank earth point was a small crack where I have clearly overtightened the cover screw at some point.
Guess when i cleaned the shower yesterday I got water in the crack and from there onto the top of the tank where it was playing silly sods with the earthing, dab of silicone has dealt with it for now and all is well with the world!
Thanks again,
Joe