For anyone else who looks for an answer to this, I had an email today from Hep Technical Support and they had confirmed that white and grey is fully compatible with each other.
Hi All,
My question is quick and easier to anyone who uses Hep20 piping.
I have lots of old fittings and piping left and I want to add to my extension in the house and I don't have enough to cover so i will need to buy more Hep. I can only find the new white kind.
Can I mix and match...