Electric shower going hot then back to normal temp intermittently

[jameslpool]

Hi, we have a Mira Vie electric shower, it's 5 years old but hasn't been used that much in that time as it's in the spare room.
We have recently been using it more as we are getting work done on our main shower.
The past couple of days, there has been intermittent times when it goes very hot for about 20 secs and then returns to normal temp. It had been fine before.

I can't see that there is any issue with flow of water to the unit.

Would this be a sign that something is about to need replacing in it, do you think?

Regards
James

 

[Johntheo5]

That's probably a 8.5/9.0kw mains supplied shower, the present mains temperature (here) is 12.3C so a flowrate of 4.4/4.7 is required to give a showering temp of 40C, What generally happens is that someone opens a cold tap somewhere and the shower flowrate falls, the TCO (thermal cut out) then cuts the heating elements power at 48C which is very hot and the shower goes cold for maybe 5/6 secs and then returns to normal when flow restored, can't really see any other (normal) reason for above except that your showering very close to that trip temperature of 48C?.
the flowrate should increase (almost double), to ~ 7.5/8.0LPM) if you turn the temperature control to fully cold. Check the filter.