Sorry if this is a frequent post (is there a read this first / FAQ ?) Our tried and tested hot water system in our B&B is causing us grief. We haven't changed anything for 5 years, but the hot water seems to be running out much faster than it was before. The age of the system is probably 25 years. It is a gravity fed system with an indirect hot tank heated by our primary boiler (in good fettle, and heating the house fine). The boiler cuts in and out according to the tank thermostat without delay etc. We are scratching our heads. Clearly we need professional help, but we want a good idea what might be wrong before we call in the (expensive) experts. Any ideas ? Any tests ?