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Discuss Best chemical flush? in the Central Heating Forum area at

  1. Cailean

    Cailean Plumber

    I've been using Fernox F3 and on occasion Sentinel X400 to chemically flush out old 8mm microbore heating systems. I've had mixed results with both products, although they generally do the job.

    I'm thinking of trying the fast acting stuff Sentinel X800, on a very old and never cleaned 8mm microbore system, which the manufacturers claim works in an hour.

    Has anyone tried this stuff or is there something even better than is recommended?
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Not worth even trying on 8mm repipe time
    • Like Like x 1
  3. Cailean

    Cailean Plumber

    Unfortunately due to financial constraints a repipe is not even an option for this customer at present.
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    TBH I wouldn't even bother flushing
  5. Cailean

    Cailean Plumber

    It has worked in the past, but not all of the time. It's worth a wee go at it to help them out. Nothing ventured, nothing gained.
  6. Best

    Best Trusted Plumber

    How about flushing solely the pipes with mains water?
    (Clean the rads by removing them)
    No sure about manifolds though.
    I have in the past flushed microbore, but by doing each rad valve into another hose.
    No doubt best repiped if possible
    • Like Like x 1
  7. Harvest Fields

    Harvest Fields S. Mod Trusted Plumber GSR Top Contributor!!

    Possible powerflush ?
  8. BYP


    Personally I hate microbore pipe. I’d do as Shaun suggested and go with 15mm. If the customer is on a tight budget though no harm in giving a go, although explain that they may be no better off. How Many rads is the?
  9. AMGasServices

    AMGasServices GSR

    I know of a friend who was a similar situation but he was given a finance option I think it was 6 months interest free.

    It helped him out with funds and has a better heating system.
    • Like Like x 1
  10. Cailean

    Cailean Plumber

    I'm going to the job today and will fully open all lockshields and TRV'S, flush out the system with fresh water, refill it and add fast acting Sentinel X800. I'll run this through the system at maximum temperature for an hour, flush it out, refill the system and balance it. If there's still a few cold spots, I'll add the Sentinel X400 and allow it to circulate for two weeks.
    The ideal solution is to rip out all the old 8mm pipework and replace the entire heating system, but unfortunately this is not a financial option for this customer at present.
    I'll let you know if the chemistry is a success.
  11. sammathias

    sammathias Plumber GSR

    X800 for more than 1 hour that's for sure. 24, hours even better. Then hot flush it. Open vented??
    • Like Like x 1
  12. Cailean

    Cailean Plumber

    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.
    • Like Like x 2
  13. Best

    Best Trusted Plumber

    Glad you achieved a big improvement.
    I used to just flush systems many years ago by using mains from a garden hose, often removing every rad and also flushing the pipes. It also achieved great results. I think still good to do this as a first clean.
    I have found the Fernox F5 good for removing magnetite. The clean looking water in a system will turn grey and a mag filter would pick it all up.
    Nothing beats removing microbore pipes and also scrapping old rads imo.
    • Like Like x 1
  14. AWheating

    AWheating Trusted Plumber GSR

    Acid would be best. X800 only works for a short time as it's designed for quick powerflush use. After a day in a system it is doing nothing more. Others last longer but are not as strong.

    Calmag do a product similar to fx2 it's only £5 a bottle. Works quite well.
  15. Harvest Fields

    Harvest Fields S. Mod Trusted Plumber GSR Top Contributor!!

    Acid cannot be used on aluminium
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