I have a hot water cylinder which is heated by an immersion heater in the summer months and a boiler (indirectly) in the winter. When heated by the boiler I get plenty of hot water for a full bath. However in the summer the heater element gets the water piping hot but it runs out very quickly. I have the old style non-resettable thermostat heater but it seems to be working as i have a live current on both terminals. Might I need a longer element? or a new one altogether? also if I do have the 11" element is there any benefit in having the 27"?