I used the X800 and it worked a treat.
I fully opened all lockshields and TRV's in the house (3 floors), drained down the system via a rad in the basement and using the fill valve on the boiler, flushed it through with fresh water on each level.
I added the X800 to a rad after removing an air valve, via a filling loop I made up a while back, filled up the system and bled out all the air on all three floors. The instructions say to fire up the boiler and circulate the X800 at working temperature for an hour, so this is what I did.
After about 40 minutes, two of the rads that hadn't been heating up for years, were red hot, as was the entire system.
After an hour, I attached my hose to the basement rad and cracked open the valve. What came out looked like jet black treacle, years of sludge and metal deposits came pouring out. I thoroughly flushed out the X800 and the years of crap it dislodged until the water ran clear.
I refilled the system, added inhibitor, bled every rad and turned on the heating. Every rad in that house is red hot now. I balanced the system throughout the house and both me and the homeowner are very happy at the result.
The chemistry is NOT a cure. It will add life to an ancient 8mm microbore system, until money is available for a repipe. A Magnaclean is now being fitted too.
I'll now offer this to customers who want rads added to their existing systems, as it does dislodge crap that fresh water flushing does not, and it does the business in about an hour.
It's no miracle cure, and won't work on every system, but for 20 quid, it's certainly an option and worth a go.
