Hi Any advice appreciated on my unusual project. I would like to get instant hot water to the kitchen sink via a small electric heater. I have a log burner with back boiler so would not want to use it when fire is on. I would prefer to have the one mixer tap. My problem is having some sort of system (maybe a valve) to isolate the electric side from the back boiler if you see what I mean. Not too sure if I have put this over correctly, look forward to any advice
I am not a plumber, these are suggestions/ideas for you to research further, not 'advice'..
You should fit non-return valves inline between (a) the cold feed to the water heater and the heater inlet (b) the hot water pipe coming from the hot water tank.
The simplest way would be to fit two stopcocks (1) in the pipe from the heater outlet and a T piece (2) in the pipe from the hw tank and the same T piece. The third connection of the T piece goes to the tap hot feed. Turn one stopcock on and the other off, and vice-versa. The non-return valves are in case you forget, so that water from the heater doesn't go back to the tank, and water from the tank doesn't go back through the heater and into the cold supply.
An alternative would be a diverter valve, you may struggle to find a simple brass one and the fancy ones may have BSP connections that you will have to adapt. These are used in a shower riser rail so that you can have a fixed head and a head on a hose, the diverter sends the flow to one or the other. They are usually chrome plated and cost about £15, it would need to be installed in rigid copper pipework to support it.
You'd need more of an expert than me but this could possibly also be done automatically with a thermostatic mixer valve, such is used in old peoples' (dementia sufferers) bathrooms to prevent them accidentally scolding themselves. IF (I surmise) the electric heater went in one side and the hw tank went in the other, the flow to the tap would draw from whichever feed had hot water in it........? Don't know.
As far as I understand: you have a backboiler, that has obviously a gas fire front. The boiler heats up the water in the cylinder and does your heating. You would like to have an under sink electric water heater for your kitchen??
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