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| how does it deliver directly to taps bypassing the tank? or does it have to heat up the whole tank on demand? | |
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It probably has a heatsink, an internal water tank or metal mass through which the water to be heated flows in pipes (like a reverse immersion heater).
Oil isn't as instant as gas, and it is more efficient and emissions friendly to burn less frequently but over longer periods. Also less likely to accidentally boil a large mass of water than the water in the heating flow pipes.
Hence the heat sink (or on our boiler strangely named "heat generator") is heated to a point above the necessary temperature for hot water or heating flow, and then when it has passed on the heat and is too cool it gets heated up again.
Our boiler allows me to see the current and target temperatures for hot water, heating flow and heat generator.
ps. we don't have instant hot water - given how well insulated hot water tanks are, not sure what the point is to have an option - instant just saves space, but if you have the tank anyway?