Immersion heater thermostat failed?

[StephenStephen]

In the past, the immersion heater would heat the water hotter than the gas boiler.
In recent months, when I put the immersion heater on, it consistently stays on for about a minute or two then switches off.
This happens whether or not the solar electric diverter is set to on or to bypass. If the solar diverter is set to on, it reports max temp reached after a minute or two.

The immersion heater thermostat is set as high as it will go. The dial on the gas boiler is unchanged.

So do I just call in our electrician to check, and if needed, replace the immersion thermostat? Or is there something else to check/try first?
For example, should I let the water in the tank get cold then see if the immersion stays on longer?

Many thanks, Stephen

 

[Johntheo5]

Is the immersion element mounted (horizontally) low down in the cylinder or is it vertically top mounted?, if the former then running off 20/30L of HW should certainly close the stat contacts, if top mounted, then you might have to drain off 2/3rds of the HW.
Most cylinder stats have a 6C to 8C hysteresis so should not stay on for just a minute or two.

 

[StephenStephen]

Thank you - it's horizontal - low in the cylinder.
Guess I'll have a bath and then check it...