Not much hot water from horizontal cylinder

[naimq]

I have a horizontal standing hot water cylinder and after the boiler goes on for 30 minutes I only get enough hot water for 1 shower. The central heating is not on at the same time as the hot water. I wonder whether there is a fault with the heating element(s). How can I check this?
Thank you.

 

[cross thread]

this type of cylinder are known to give a poor volume of h/water,try setting boiler stat and cylinder stat higher