I have another thread relating to heating that I'd gone a bit off topic into DHW so thought I'd start something in the right spot to request advise and opinion.    Current setup : immersion. Probably 20 plus years old. Not easily accessible to insulate further. Very little control - we added a timer to reduce energy use  Wired to economy 7 only so no mechanism to top up outside eco 7 hours.  Mains Flow rate - 1 ltr every 2.5 seconds  Pressure - not known a