I have Worcester 25i combi boiler. The hot water supplied by it is hard to use mostly because it's min water flow requirement is too high and when you adjust the hot water tap so it decreases the hot water flow below requirement the boiler stops producing hot water at all. I considered an electric water heater (I thought of Ariston Oversink Water Heater 3kW 15Ltr (5106G) from ScrewFix) to be connected just after the output of the boiler's hot water, so, it will not consume much electricity, but still provide hot water with no minimal water flaw requirements and without gaps of cold water if you switch water off and back on. I asked a plumber to install it and he said it cannot be done. He claimed it was not allowed legally, but even if it were, it would not work like that because of valves that stop reverse water flow. He would have no problems If I wanted to connect the heater to main cold water supply. He is a certivied unvented hot water tanks installer. So, I wonder, can it be done at all? It would be the cheapest solution to my problem. If not, what other possible options I have? An expensive one I know myself already - replace the boiler and install unvented hot water tank. I am really considering it as hot water suppy from my Worcester 25i is unusable, but I am still paying for my current boiler. I don't want to install "instant" electric water heater as they are not instant and I will also need to do special wiring to it and it will cost me probably more than replacing the boiler. I called a Worcester engineer and he measured everything and said the boiler operated within its limits as specified in the manual. Thanks.