Hi all, apologies for the novice but wanted to check some basics before a call out. I live in a rented property and have just moved in. The heating kicks in instantly when I use the digital thermostat but the hot water is delayed. For example I've run the shower for 20 mins to get luke warm water this morning and the preheat indicator took this long to come on. Often we get hot water at the taps then it stops and runs cold for minutes before becoming hot again and this repeats. We can't get enough hot water to fill the bath. Cold water flow seems fine. Any ideas?