Change from System and tank to Combi

ChrisJP said:

That assumes that the delayed HW is solely due to lack of water flow. With a combi boiler and HW on demand, the water flow is limited by the capacity of the boiler to heat it dynamically. Speed up the flow too much with a secondary pump and the HW will just be lukewarm.

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Secondary pump on an unvented cylinder NOT a combi boiler
OP has a heat only boiler and cylinder.

Winter second pump maybe a good idea, but in summer, any heat into the house means AC runs for longer, so don't want the second pump. And it is not just a second pump, but flow and return, so extra pipework as well.

To lag the CH and DHW pipes together may again work in the winter, but not in the summer. Also to was hands 10 mm pipe work is ample, but not to run a bath. Even then down to boiler size, if the boiler can't deliver full bore with a 28 mm pipe, no point in having it that big.

I wash my hands likely 5 times a day after going to the toilet, but shower is instant electric, the washing machines (clothes and dishes) are cold fill, so between each use the water has gone cold. And often I will not wait for the hot, so that water drawn into the pipes just heats the house.

I like the reservoir of water, be it a tank, cylinder, or cistern does not matter. If the water goes off, I still have enough for a week or two. But I would if starting from scratch, likely have a different system. Smaller pipes for sure. But not starting from scratch, so will keep it as it is, not really worth changing.