Electric shower only produces scolding hot or ice cold in hotter months. Any idea what I can do to fix this or is this normal?

[endecotp]

I will admit am sensitive to heat

Right....

Get a thermometer that you can use to measure the water temperature.

 

[Alec_t]

I'll give it a few quarter turns. Its currently turned to 12-6 position with the pipe running vertically. ill give it a few turns

If it's the usual isolator/service valve then it's a quarter-turn type. The 12-6 position is fully open (and the 3-9 position is fully closed).

 

[jj4091]

It still seems like the problem is the flow rate either into or out of the shower unit. See these instructions about flow rate and maintenance.
https://www.bristan.com/product-files/576763/fitting-instructions.pdf perhaps you just need to clean both filters

If you can achieve the required input flow rate but not out then it would suggest that the stabiliser valve is is either blocked or faulty

Google Search

 

[Johntheo5]

Eco power setting on most showers is generally ~ 60% of full power so yours certainly shouldn't be greater than say 5.0kW. At a present mains temp of 17C it only requires a flowrate of 3.12LPM to have a comfortable 40C shower, if it's just about reaching its cut out temperature of 50C, but isn't, then the flowrate can only be 2.17LPM or less. A healthy shower should flow between ~ 2.0 and 8.0LPM MIN/MAX temp control settings.