System blockage

[pault123]

I installed a new 28 rad sytem (Ideal concorde 240) 8 years ago. The first 3 rads on the system have suddenly gone cold.
Each of these has individual flow and returns through the screed in Hep20 run to an accessible part of the cellar where the common pipework is.
I disconnected each flow and return and flushed through from the mains in both directions. I got loads of crap out the returns but the flows are blocked solid with just a dribble of water coming through.
The debris (magnetite ?? - it is magnetic) from the returns is gritty but the system water is really clean - no sign of sludge. Is this likely to be from the boiler which would have been difficult to flush as its in a cellar. MB1 was added from day one and its not been drained since the initial fill and flush.
Will a power flush with positive/negative pressure and reverse clear this, where the mains may have just compacted the debris at the first elbow (damn those Hep20 inserts !).
I really want to avoid digging up the extremely decorative/expensive tiled floor.

Any suggestions and if power flush is the best option what unit (Kamco ?)& chemicals to use. Its fairly easy to isolate this section of pipework from the rest of the system.
Thanks

[Chris]

Odd that it's collected all that in a new system with inhibitor.

Flushers aren't particularly high pressure - the Kamco normal one is about 1.4 bar. Fernox and Sentinel are higher iirc.
But as long as there's a dribble of flow, a chemical such as Kamco's FX-2 should help get things going. If you're ONLY flushing a piece of pipe you could use something stronger which you wouldn't want to get into the boiler. Kamco do an inhibited hydrochloric acid based chem. It would be worth talking to them, they know their stuff.
If you have access to an "end" where there isn't immediately an elbow, you could try a thin sani-snake down the pipe. The cheap ones ( about 6-8mm diameter) you find in "Pound" shops would go a few feet, I have one which is 5 metres.

[SimonD]

For you to have sludge in a system 8 years old that's never been drained I must assume you have an 'open vent' system.

If so, it has either been pumping over or you have a leak.