No hot water from electric shower

[Tudor]

Afternoon

I have a Mira Azora electric shower (J95L 03/22)

Yesterday, after showering, I pressed the on/off button to turn the shower off. Water stopped flowing and then a noise started, similar to a kettle boiling dry. 10 seconds later it dumped a load of scalding water from the shower head.

Since this event, the shower isn't producing any hot water although it still switches on/off and provides cold water from the shower head.

I am looking to replace the Thermal Switch, but not having any experience around electric showers was after opinions as to the fault please

Cheers
Dan

 

[Diver Fred]

Was the dump of water Clean or dirty? If it was clean then it sounds like the overheat switch. That may have a manual reset in the shower unit.
If dirty then it is probably the element.

It is always best to turn the heat switch to cold and allow the water to cool/go cold before switching the shower off completely.

 

[Johntheo5]

Afternoon

I have a Mira Azora electric shower (J95L 03/22)

Yesterday, after showering, I pressed the on/off button to turn the shower off. Water stopped flowing and then a noise started, similar to a kettle boiling dry. 10 seconds later it dumped a load of scalding water from the shower head.

Since this event, the shower isn't producing any hot water although it still switches on/off and provides cold water from the shower head.

I am looking to replace the Thermal Switch, but not having any experience around electric showers was after opinions as to the fault please

Cheers
Dan

Sounds like a microswitch has stuck on, sometimes, then, the first stage trip in the TCO will operate at 48C/50C and will reset either when you press the start button (after some cold water flows through the heating can) or up to a hour later, automatically, if the microswitch is still stuck on then a repeat of the above until eventually the water will be boiled out of the heating can and the non resettable second stage will/should operate at 75C to kill the power permanently. I would suggest checking or get checked both microswitches with a m.meter to see if one or both closed, you will then have to renew the failed one before renewing the TCO.

 

[Tudor]

The dump of water was clean.
I'll see if there's a manual reset switch.

 

[Johntheo5]

Just had a look at the MIs, your shower has two TCOs, one (self resetting) is in the outlet and the other non resettable one is on the heating can, that shower also has a phased shutdown where the heating elements are switched off but the water continues to flow for a some seconds to cool down ready for the next user.

 

[Tudor]

Continuity testing of both micro switches has passed

 

[Johntheo5]

You've proved both microswitches OK, presume you are saying that there is NO continuity (now) so difficult to see what's causing the problem, have you checked the continuity of the TCO, if its open then no continuity and needs replacing after fault is found. When you shut off the shower yesterday, did it keep flowing for say 10 secs or so, and when the shower was working normally did the flow continue on for awhile as it should during a phased shutdown? Won't tell alot but might be worth measuring the flowrate when turned to fully cold, would expect ~ 10 LPM.

Apoligies, your shower doesn't have two separate TCOs, it has the two stage as stated in my first post,

 

[Tudor]

Sorry John.........got waylaid with something else which is broken.

Continuity testing of the TCO has failed.
I'll order a replacement

The shower usually flows for another 5 seconds or so when powered off, but yesterday this didn't really happen......just made the strange "boiling kettle" noise and chucked out boiling water after 10 seconds.

Hopefully the replacement TCO switch will fix it

 

[Johntheo5]

I hope so Dan but hope you don't just end up with another blown TCO.
This shower's PCB probably control relay(s) that make/break the power to the heating elements so suggest to start up the shower (after replacing the TCO) on its no power setting and see if it runs cold, then while still running, switch to full power and see if the shower temperature increases to normal, if so, then switch back to the no power setting and see if the shower temperature again runs cold. Maybe then try running as per normal.

Do you have any limescale in your area?, all simple "normal" showers don't have a phased shutdown but you will clearly hear the 48C trip clicking off about 10/12 seconds after switching off the shower and you might get a few drops of water from the shower head, I've only seen one that tripped the 75C stage and found its heating elements and can with large deposits of scaling.