On Wed, 4 Mar 2020 09:10:07 +0000, Chris B wrote:

However on the cold side the entire volume of the cold supply pipe
inside the house (2 or perhaps 3 litres) will be warmed from 5C to house
ambient - say 20C. This must cause some expansion (volume increase may
only be an egg-cup full) and I am curios as to how this is dealt with.

The coefficient expansion of Water is highly nonlinear but from 10 to
20 C it's about 0.0001 / deg C. So 1 litre of water warmed by 10 C
expands by about 1 ml.

I'd be surprised if your incoming underground fed mains water is as
cold as 5 C even in a severe winter. 10 to 15 is much more likely.

--
Cheers
Dave.