How to unblock SOLID 15mm central heating pipe and rectify a banging boiler

Discussion in 'Plumbers' Talk' started by Bento, Mar 8, 2019.

  1. Bento

    Bento New Member

    Beware..... long post.....

    I have 2 rads on the second floor of my house that have been cold/lukewarm for years and I've just got it sorted after a huge amount of work so hopefully this may be of some help to anyone in a similar position!!!!

    After trying all the usual stuff (before I concluded that they were blocked) e.g. balancing the system, bleeding the system, trying to force flow to the cold rads by closing every warm rad, uprating the central heating pump, flushing the affected rads, checking the rad valves were functioning properly.... I concluded that the pipework must be blocked:(. I confirmed this by placing a magnet on a piece of copper pipe and getting a magnetic force (which indicated a ferrous material must be inside the copper). So here's what I did.....

    The 1st floor and 2nd floor rads are on the same zone and all 1st floor rads were hot but the two on the 2nd floor were lukewarm/cold. So I concluded the blockage must sit between 1st and 2nd floor. After much huffing and puffing and furniture and carpet moving, I managed to locate the pipe connection points. When I did this I could see that the 2nd floor system had been added at a later date from the rest of the house as the main pipe runs were all copper and the 2nd floor was all plastic. These plastic pipes had also been laid to create a natural low spot (which I think is significant as it acts as a settling point for sludge when the water isn't circulating).

    I disconnected the plastic pipes from the copper ones to isolate the 2nd floor. I then connected a hose to these plastic pipes and tried to blast flow through (from an external tap - starting at low flow and slowly increasing to max flow). I did this from both 1st floor upwards (with discharge to 2nd floor) and from 2nd floor downwards (with discharge at 1st floor). Both of these were unsuccessful. I then cut out a section of plastic pipe on the feed (hot) side underneath the 1st floor floorboards, and I could see the pipe was ENCRUSTED with sludge build up. After cutting out a section of pipe on the 2nd floor I could isolate a length of pipe approx 3m long, buried in the wall, that must have been blocked (i.e. when I connected the hose to this no flow would come out of the end).

    Next off I bought myself a 6mm diameter pipe of rebar (I could only find a 2m length - £3) and rodded the 15mm pipe from the 2nd floor down towards the 1st floor. I then used a coat hanger from the first floor to pull as much sludge out as possible. I repeated about 10 times (hands in agony!!!). I then used a 4m piece of tough garden wire and threaded/forced it through from the 2nd floor down. Eventually I was able to pull the wire through from the 1st floor and out came more sludge. I then connected a bike pump to the pipe and tried to blow air through but with no impact. I then re-connected the hose from the external tap to the pipe and turned it on (slowly increasing the flow). After about 30secs a huge glug occured and black water came out :) I left it running for about 10mins to clear as much sludge as I could. I reconnected all the pipework, recommissioned the system and hey presto! the rads on the top floor were all working!

    But it doesn't stop there :(...... after a couple of hours my boiler started to make very loud banging noises. After a bit of YouTube and web research I concluded this must be 'kettling' (debris blocking the heat exhanger.... which seemed logical as I'd been clearing sludge from the system and there was bound to be some in there). What I noticed was that if I turned the thermastat down on my boiler it didn't 'kettle', so it only seemd to happen at higher temperatures. So I put some cleaner in the system (I was intending to anyway after a few days of sorting the system). Initially the noises didn't subside but I knocked the thermastat back to min and ran it for about 8hrs. It apears to have cured the problem!!!:) I'm currently in the process of ramping up the thermastat slowly (over the next few days I'll get to max) so we'll see how we get on.

    Basically..... if your pipes are blocked solid I think you have a few options once you've located the blockage....
    • try and flush from mains water pressure
    • cut out the blocked pipe (easy if its accessible, but if it's buried in a wall you may face a big redecorating bill)
    • rod the blockage (not as easy as it sounds - you'll need something like rebar as long as it's not blocked on a bend)
    • powerflush the system (I'm honestly not sure it would have solved my bloackage)
    • accept cold rads in one part of your house :(
    At some point soon I will powerflush the system to get more sludge out - particularly if the kettling comes back. If I need to get a new heat exchanger or boiler I'll powerflush BEFORE doing so as I don't want to risk blocking a new one. I'll continue to clean my magnetic filter daily as well.

    Sorry for the long post - hope it helps anyone. Good luck.

    JB

    PS - the reason rads occassionally got lukewarm was because of natural convection within the system.... it wasn't because any flow was reaching the rads. The rads were filling from the return (cold) pipework.
     
    wh22 and Wayners like this.
  2. KIAB

    KIAB Super Member

    First I fit a magnetic filter (Magnaclean Pro 2 among the best & easiest to fit) on the CH return,add Sentinel X400 cleaner,leave in for two weeks,it will not clear blockages, but should help move crud, this would collect any crud rather than recirculating it around the system.
    Good thing with the Magnaclean, you can remove filter & connect a Magnacleanse to system & it will collect any crud, beter than a powerf flush, gentler on your system.

    A steel draw tape is brilliant for clearing blockages in pipes.
    You could try clearing a section at a time,remove radiator,connect hose to either lockshield or trv end & run to outside drain,then flush that section,repeating process around the house, also take radiators outside & flush out with hose.

    If pipes are buried in wall, then repipe,easiest option.
     
  3. Heat

    Heat Screwfix Select

    Bento, have you checked if your plastic pipes in system are all done with barrier pipe? If incorrect pipe only suitable for hot and cold water, then they will block solid due to ingress of air through pipe walls.

    In an ideal world you are best with a sealed system if gas or oil system (combi or heat only boilers), no plastic pipes because they absorb air and tend to have other problems, a magnetic filter installed perhaps and inhibitor in system.
     
  4. Bento

    Bento New Member

    Thanks KIAB - I have recently installed a magnetic filter so I'm hoping this will pick up lots of the sludge. Never come across steel draw tape but sounds like a good option. I desperately didn't want to re-pipe because I would need to chisel out OR run the pipes external to the wall but accept that it would be relatively easy (if external). The blockage has defo cleared so it's now just a case of hoping the 'kettling' subsides given the clearner that's in the system I've used Sentinel before but this time it's Corgi (that's what Toolstation supply).

    Thanks again!
     
  5. Bento

    Bento New Member

    Heat - thanks for this advice. The existing plastic pipe is Hep2o and 'stamped as 'suitable for central heating'. The pipe I installed is barrier pipe. (Phew!) My system is sealed and I have recently installed a magnetic filter. Thnaks again for great advice.

    Plumbing is much harder than people give it credit for:) (I'm a lowly DIY'er)
     
  6. KIAB

    KIAB Super Member

    A steel draw tape is usually used to pull electric cables through conduit,but I found it perfect for unblocking a 22mm pipe from a F & E tank in loft,usually you would replace the section of pipe,but as access was almost impossible,I just remove gate valve from pipe,& had a moment of inspiration to use a draw tape, as it was the only thing I had,that was flexible & long enough to feed up pipe.:)
     
    Last edited: Mar 8, 2019
    Bento likes this.
  7. Heat

    Heat Screwfix Select

    An old speedometer cable out of a car is excellent due to being very flexible, yet very strong. Goes around bends really well.
     
    Bento and Astramax like this.

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