22mm or keep 15mm?

Discussion in 'Plumbers' Talk' started by anthnewman, Jan 8, 2013.

  1. anthnewman

    anthnewman New Member

    Hi all, another newby for you to savage!!!

    I have bought an aqualisa digital bath filler, my water supply is via a conbi boiler, it states in the instructions it recommends i fit a 22mm pipe as close to the hot and cold inlet as possible (15mm inlets so happy to reduce back down.

    I pressume (good DIY word) 22mm will give enough supply for demand? however it does not state what length this 22mm pipe should be? As the outlet is 15mm, will it make much difference if i did not use 22mm and keep the inlets at 15mm?

    Any help much appreciated!!
  2. Aren't there two models available - one for high-pressure (combi) systems, and one for conventional low pressure (storage tank) systems - the latter coming with a built-in pump?

    If you bought the correct one, I'd have thought that the current 15mm pipework would be fine. Combi systems tend to use 15mm pipework because the mains pressure behind the flow will easily deliver the full water flow down this size of pipe. Very little benefit from up-sizing to 22mm.

    Check with Aqualisa is you are uncertain.
  3. anthnewman

    anthnewman New Member

    Hi, thanks for the info, i got the right one for a combi / pressured system, i just found it strange that it still states 22mm should be used for the inlets? i have some 22mm from the old pipework so might just fit 1 meter or so for each inlet? My only other problem i have is i do not know my water pressure for cold into the baxi combi, the Aqualisa should only be fed with max pressure of 6 bar. I take it i will need a pressure gauge and fit it to a cold outlet pipe? If it is too high then i have to fit a pressure reduction valve prior to the cold feed entering the combi, happy with that.

    Thanks again

  4. Captain Leaky

    Captain Leaky New Member

    I have fitted these on combis and always use 15mm. It will be fine.
  5. Crowsfoot

    Crowsfoot Screwfix Select

    Long cold water draw off times and low flow rates are issues with combi boilers and I would have thought having 22mm pipework would make matters worse the more you have.
  6. I can't see 22mm pipe affecting the flow rate - except to fractionally, barely perceptably improve it - but it will delay the hot water coming through as there will be more cold water to shift first.

    Anth, you worry too much. Fit the 22mm pipe for a metre length if you have it - no harm, and you'll feel better inside...

    6 bar is high, although certainly not unheard off. If it does turn out to be higher than that, you simply have a PRV fitted on your incoming water mains - they cost, ooh, around £20+ and many come with a pressure gauge on them so's you can tweak it to what you want.

    If you have 6 bar pressure, I think you'd know about it - you'd wet yourself every time you turn on your kitchen tap (through splash-back or fright), and cisterns and taps would tend to be a bit noisy.

    Don't take it personal, like, but I doubt you have it .
  7. anthnewman

    anthnewman New Member

    Thanks all for taking the time to respond, all seems well with the pressure etc, it takes a while to fill a hot bath but thats a combi and does the same with standard tap set up!!
  8. Cool.

    Yep, it wouldn't make any difference whatsoever whether 22mm or 15mm pipe was used, so it's strange they suggested 22mm even with a high-pressure system - unless that's just a misprint or copy-over from the 'low-pressure' instructions?

    And, yep, a bath will take longer to fill with most combis compared to a 'stored' system as using the hot tap has quite an effect on the cold water flow too. On a storage 'vented' system, the hot and cold are fully independent, so you can have them both full-on.

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