Grohe electric shower issue

[Burnerman]

I have a Grohe Tempesta 8.5kW shower - it's not used often.
When the shower is switched off, the hot water flow immediately stops. Occasionally it gives a spurt of very hot water seconds later (I'm told).
Switching it back on again, the auto reset lamp is lit for a while, and it passes only cold water until the lamp goes out - maybe 15 sec or so.
I seem to recall it used to run for a few seconds before shutting down, presumably to lose hot water from the water boiler.
I know that this shower has a 'phased shut down' relay, and also a 'phased shut down' PCB. I don't know how reliable these things are.
If anyone could point me in the right direction to sort this, I'd be very grateful!
Cheers and have a good evening everyone
John

 

[jj4091]

Are you switching it off just at the shower or an isolator ?

 

[Burnerman]

Just at the shower, jj.
John

 

[Johntheo5]

It seemes to be behaving like the normal non phased shower, when you switch one of these off the water stops immediately but you will get a dribble (but not a spurt) of hot water for a few seconds, if you listen (with shower off) you will hear a click ~ 10 seconds later, this is the thermal cut out, TCO, operating, it probably takes a 1/2 hour or more to reset if you don't switch the shower back on. If you do switch on the shower a few seconds after stopping it then it will run extremely hot for a few seconds, then run cold (TCO) has operated for maybe 10 secs and then will heat up normally over 10/15 secs. If I know that someone is waiting (not very often) to use the shower straight away, then I switch the power selector to cold for ~ 10 secs before switching off, after switching off, I then return the power switch to normal.
This won't fix the above shower though.

 

[Burnerman]

Thanks John
I’m tempted to replace the phased PCB, the fault seems to be in that area, and I would have thought that a relay fault would cause the shower to not function at all or to be flowing constantly.
The darn thing seems to be obsolete now but these parts are available.
I like your idea of running the shower cool, a good safety technique.
I appreciate your interest!
Regards
John