Interesting discussion ongoing on Pistonheads Forum, Home and DIY section. There are some muppets here but also some very knowledgeable people who have gone through the regs with a fine toothcomb and assert that provided you are not doing it for profit/reward or for someone else, then...
I have an Intergas Combi installed 15 months ago to the loft of our bungalow and have been installing new drainage for a bathroom and en-suite with an internal stack.
I took the opportunity to connect the condense drain (32mm) to the new internal stack to reduce the dreaded freezing risk and...