Well timed Dan as I just found two copies of the spec in a file. New systems and refurbs. Doesn't ask whether a flush is needed simply states there must be one before the work is started on replacements.
First the contractors. There's loads of money in each allocation but the majority is eaten up by admin. and checks and asbestos, electrical works and other things. Not defending it just telling you how it was.
As soon as criticism came efforts were made to reduce costs and of course that included laying off staff and reducing rates. When I left all the fitters took a big hit or hit the road if they could find anything else at a time when there was little else away. Not excuses but reasons.
Anyway the spec.
From Specification for the Repair of Gas Central Heating Systems and replacement boilers. Known as TS110 issued by eaga and what the contractors quoted on.
This is dated 2003 but I have revisions up to 08. It hasn’t changed much I’d guess since then if at all.
I can give you some quotes.
Page 5: section 1 Overall requirements:
Ensure the client is satisfied with the work.
Page 6:
Comply with Building Regs Parts B,F,G,J,L1,L2,M,P.
Page 7:
Comply with British Standards. The one you’re interested in is BS 7593 Treatment of water in Domestic Hot water Heating Systems
Page 12:
System Flushing: Prior to commencing any rectification or boiler replacement work the existing heating system will be flushed and rinsed to clean the pipework and radiators etc. This is to remove sludge and accumulated corrosion products etc from the system.
I think the word WILL is operative here. Remember BS 7593 allows power, mains water and gravity flushing so any will do but the TDS must be within 10% of incoming mains when complete. More than 20% system must be flushed again. (I’ve always wondered what you do between 10 and 20%!!)
A proprietary agent must be used and I think the choices were Sentinel and Fernox products.
Where flushing equipment is used (as per manufacturers instructions) it is to be used but only for a duration that will ensure the removal of the majority of the dirt.
Next paragraph:
The flushing process may need to be continued where subsequent checks show that the heating system is still not clean enough.
There's enough there for the OP to put the matter to bed.
I also note the requirement to comply with Part L which has been mentioned here many times.
Sometimes I dream my whole world is held together with cable ties.
Now for the football