Domestic Electric shower

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Hello all
Went to a call out today where shower would heat water fine on medium setting but once it was set to higher temp it would cut out. Mcb remains in and supply still present. Is there some sort of cut out inside shower if the water pressure is low?

First time I've seen such A fault


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  • #3
Had exactly the same at my house a while ago. Was told by my plumber that most showers have a thermal cut out built in so if the water pressure is too low or there is no water at all, it protects the element from damage by cutting the supply.
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needs a certain amount of water flow to stay made. somebody flushes the bog. shower goes cold.

Richard Burns

Probably the element inside is furred up and when set to full temperature the element overheats because the heat does not go into the water and the thermal trip trips.
The flow rate would not change on changing the temperature, but if the flow is low then the element may still overheat because the water is not passing it fast enough to cool it, but I would expect this to cut out because of low flow at any temperature.
I get called out to these every summer. Once the incomming water supply to the property heats up by a few degrees as the ground gets warmer (only mid to late summer after a couple of hot weeks) then the shower tries to raise the water temp by the same amount that it would with the colder supply. (as no-one bothers to try and adjust the controls) This then operates the overheat cutout to keep the user safe. If the water pressure cannot be increased to compensate then just use half power and adjust for temp with the flow rate dial.
You answered your own question without knowing it really, 'would heat water fine on medium setting' If it heats it fine then why use full power?
Once the incomming water cools again in sept then turn it back to full heat.
Years ago before the days of variable pattern handsets, (in my dads day) showers were supplied with summer and winter rings for the handset to vary the water flow in order to compensate for the summer/winter change in incomming water temp.
Hope this helps, it's explaining to the customer that there is nothing wrong with their shower yet they stiill owe you for a call out that's the tricky part, tell them it's better than an expensive flow valve or new shower!
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  • #9
Most modern shower units have two or more heating elements in the heater tank, one for each heat range of the shower. It is common for the highest power heating element to fail first as it tends to be used most often, particularly in the winter months. The condition of the elements can be assessed with continuity and insulation resistance tests. Remember to disconnect the control circuitry from the heater elements before testing to prevent damage to sensitive electronic components and/or misleading results.
Hi, in it's failed state did you test the solenoids resistance? A faulty solenoid would cause problems with low flow which if faulty would shut off the water going through the shower, think a shower solenoid resistance should be above 3ohms. Worth a quick try.


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  • #13
I had this problem and it just needed the shower head de-scaling. Sometimes the problem is simple but not obvious.
All the above could cause your 'fault' or it could just be that on full power the element will heat the water up to above the temperature limit of the safety cutout. If a satisfactory shower temperature and flow rate is achieved with half power I don't think there is anything wrong with it.
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