yes. Incoming water temps vary from around 12-14C in summer to 5-9C in winter. But its not a huge difference.
Likewise HW tank losses will be a little greater in winter of the tank is outside the insulation barrier as mine is.
Of course hotwater inside the insulation, is, until you drain it down the drain, just more heat input to the house.
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System and heating only boilers generally will, so long as the tank HE has enough transfer power. With combis it caries more - a number of manufacturers do models that do and don't - so you need to read the specs carefully.
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