Heating system flush

Heating system flush
I have an air to water pumped underfloor heating system for an area of 162 square metres. It was installed seven years ago and the system was flushed after installation. It has been professionally serviced annually. After the last service I was advised to have it flushed again due to ‘sludge’ in the system. I assumed that the annual cleaning and topping up of additive solutions would be sufficient. However, I’ve seen what the engineer drained off and it looks like a rusty coloured liquid. No idea what’s caused it or whether the problem will just return again after a flush.
So, is there anyone out there who can a) make any sense of this and b) has any idea of the cost of a flush.
Many thanks

Last September I was quoted 280 euros to flush our CH system (18 rads).

BTW, I had a magnetic filtration filter fitted last year.Central Heating Filters _ Central Heating _ Screwfix.pdf (604.8 KB)


I go with Nigel, fit a magnetic trap makes everything last longer and make sure the correct anti corrosion additive is put in for your equipment.
Additives do change the colour of the water so be careful it is rust and not a con trick, the plumbers should have a test kit and be able to demonstrate the level of anti corrosion additive in the system.

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We’ve got U/F water heating and after 5 years the water inside looks ‘rusty’. I’ve bought an Adey Magnaclean and will fit it after this heating season. Simple enough. Previous years I’ve flushed through by connecting each zone up to mains water (reduced pressure to 2bar) but even so the water looks brown. Suspect the problem is in the reservoir tank which had previously been used in a radiator system - i.e. high (~55C) rather than as present (35-40C).

Hmm any system corrosion inhibitor in there? Vital and vital to get the correct one, one of our HVAC engineers used the wrong one and rotted out the heat exchangers.
Underfloor is usually plastic pipe so clean, its the mucky boiler and other components so sometimes worth fitting a heat exchanger to keep them separated and much shorter to flush when needed and less inhibitor neeeded.