larger pipe to microbore

Discussion in 'Plumbers' Talk' started by 81misfit, Nov 10, 2019.

  1. 81misfit

    81misfit New Member

    can you in theory add larger pipes to a microbore system (8mm)? or will it screw it?
    have a pressurised 8mm system and a radiator thats too big and/or a damaged pipe.

    spoke to a few people some said pipe is kinked rad should work, others said rad is too big, and one said adding bigger pipes to the existing system will cause the rest of the radiators in the house to stop working properly - is this the case if so why has nobody else said this!!

    wish there was a slight consensus as to if this is a bad idea or not. just want a warm home.
  2. KIAB

    KIAB Super Member

    I hate microbore & 8mm is the worst.
    Usually other way around,step down from large to small.
    Joe the Plumber likes this.
  3. Jimbo

    Jimbo Screwfix Select

    How long is the run on 8mm and what size is the radiator in terms of kW?
  4. KIAB

    KIAB Super Member

    He fighting a losing battle with the 8mm.
  5. 81misfit

    81misfit New Member

    around 2.4kw (90% sure) run is maybe 7-10m? not 100% on the route of the pipe as the manifold is at the top of the stairs and rad at bottom. think it runs through the bedroom and down.
  6. 81misfit

    81misfit New Member

    should add, inital plan was to come off before the manifold on the 22mm (nearer boiler) and cap off old 8mm pipe. not come off a 8mm pipe and widen to 10 or 15. could this scupper the entire system.
  7. The Teach

    The Teach Screwfix Select

    The system may just need balancing but first approach is to turn off all the working radiators and see if the luke warm heats up any better :).

    you need a heating repair technician to visit and work out the problem,its very to diagnoise circulation faults. Some onsite tests can be carried out,these will be bespoke to your installation ;).

  8. 81misfit

    81misfit New Member

    tried both. no change (a hair warmer but might just be wishful thinking).
  9. Joe the Plumber

    Joe the Plumber Screwfix Select

    I'd check your central heating pump is working properly. They can be the cause of untold problems if they're on their way out or simply sludged up. Bear in mind your radiator is effectively a series of big, open pipes. It doesn't really care much if the pipes feeding it are big or small.
    Heat likes this.
  10. Heat

    Heat Screwfix Select

    And ignore what people are telling you about replacing 8mm to 15mm ruining rest of system.
    It won’t if the new pipes to rad are carefully balanced by closing the lockshield rad valve down
    Joe the Plumber likes this.
  11. Jimbo

    Jimbo Screwfix Select

    I ran some calculations. Drawing 2.4kW at 20* dT gives a water velocity of 0.8m/s in 8mm and a pressure loss of 80mBar over each 10m leg.

    10mm pipe will halve the pressure loss and 15mm will reduce it to 5mBar.

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