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Megaflo - rubbish shower pressure

Discussion in 'Plumbing and Central Heating' started by robatwork, 8 Jul 2019.

  1. robatwork

    robatwork

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    Hi all,

    Don't know much about plumbing so please bear with me.

    Moved into a house that has a Vaillant system boiler and Megaflo 300L cylinder in the loft.
    Water pressure into the house isn't great at 2.5 bar and 15L flow, and it's shared with 3 neighbours.

    There's a bath downstairs that gets 14L cold and 20L hot flow which is just about OK.
    The shower upstairs gets a rubbish 8L for both (no nozzle), with the nozzle it's like standing in a light rain.
    The taps in basins get between 4 and 7L, nothing like "mains".

    I thought a megaflo made all taps the same pressure - so do I have a faulty megaflo, or need to get the pipework or shower mechanism looked at? Or is this just caused by the mains not being powerful enough and I need either some sort of water booster/accumulator or even get a dedicated 25mm feed from the mains instead of the 15mm shared one. Obviously don't want to go down that last route unless is guaranteed to help as it will be really costly.

    Grateful for any expertise.
    Rob
     
  2. oldbuffer

    oldbuffer

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    1. If the cold feeds to everything except the kitchen sink are taken from the cylinder's combination valve, then hot and cold pressures will be the same. If not, then cold may well be higher than hot.
    2. Sounds as if there is some mis-measurement if you can get 20 lpm from the bath hot when the incoming mains flow rate is a maximum of 15 lpm.

    The megaflo, like all unvented hot water systems, requires servicing every year. If this hasn't been done I'd suggest it's you first port of call in identifying the issues. Once serviced, get the mains pressure (static and dynamic) and flow rates checked.
     
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  3. ianmcd

    ianmcd

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    you cant get 20L/min anywhere if the incoming mains is only 15L/min
     
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  4. robatwork

    robatwork

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    I probably need to measure it again!
    The water company measured the flow rate with a proper device, I am just filling up a jug in 6 seconds and x10.
     
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  5. ianmcd

    ianmcd

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    you can not get more out of a tap than you have coming in to your house , not rocket science, when you measure the flow rate you have to run the tap and wait untill the flow is a steady flow then measure it, you wont be able to do it from scratch in 6 seconds
     
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  6. robatwork

    robatwork

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    OK Ian - thanks.

    I redid the measurement and it's 15L hot into the bath. So the fact the bath is the same as the incoming mains but the shower isn't presumably means the MF is performing OK but there's some restriction either with the shower itself or the pipe going to it?
     
  7. undertrained

    undertrained

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    What showers are you talking about? If electric then flow rate is significantly reduced.
     
  8. robatwork

    robatwork

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    The main shower is upstairs where there is a big showerhead and also a handheld. There's also a handheld in the bath downstairs. The one downstairs has better pressure than upstairs. If you aim the upstairs handheld at the ceiling it just sprays about 5cm up and then falls away. I'd expect it to soak the ceiling!

    Nothing is electric.
     
  9. terryplumb

    terryplumb

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    Check the filters in the shower are not partially blocked.
    If basin taps have flexible hoses ,examine them for sharp bends/ twists,which would reduce flow. Also check the end of the tap spout ,some taps have a section that can unscrew off the spout ,and contain a fine mesh that can block up.
     
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  10. dilalio

    dilalio

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    Try swapping the downstairs handheld with the upstairs one just to rule out the hose and wand, then it could be restrictions within the upstairs valve and/or pipework from the UV to the upstairs being restricted or a convoluted route. Your incoming mains flow and pressure is not great for a UV setup and you will also lose some of that as you go higher up the house.

    We did a job last year where it was considered that the pipework from the downstairs mains up to the UV was causing issues with pressure and flow as it was fairly decent at an outside tap (not great but fair) and running a new rising main would improve things... This would have meant a lot of disruption and opening up building fabric, so we ran a temp 25mm mdpe up the outside of the house from the exterior tap and directly into the UV control group.
    It made very little difference to the performance of the hot and cold supplies to outlets on that floor and below.

    Location of property was in a high up part of North London, notorious for poor flow and pressure at the suppliers stopcock so it was deemed upgrading main from street would be an expensive and pointless exercise.

    The solution was to install a pump and accumulator next to the UV and hide it all in some fitted wardrobes. Took up a lot of the "spare" room and there was also the noise issue of the pump when running, but we dealt with that as much as possible via timing and sound proofing.

    Customer didn't really have much of a choice and the performance was a vast improvement, which was his priority.
     
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  11. DP

    DP

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    Right away a few questions arise.

    You are sharing the mains supply with others. If mains pressure poor, it will get worst when others using cold water
    If incoming mains is 22mm, is it 22 all the way to the cylinder?
    Are hot and cold balanced feeds.
     
  12. Madrab

    Madrab

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    I'd advise getting someone who is experienced ( + qualified) with advanced hot water systems. You need the system checked at several different points to understand what's going on, check filters/PRV's etc and obtain a confirmed starting point before fault diagnosis.

    You may have that flow at certain points but has the pressure been checked? The key component with your un-vented system alongside flow is mains dynamic pressure. You only get out what can be put in.
     
  13. jonbey

    jonbey

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    I know nothing about plumbing, but I had a megaflow in my last house and next to it (above) was a red cylinder that a plumber told me was something to do with water pressure for the shower.
    So maybe you need a magic red cylinder thing. Just Googled it, I think a bit like this - http://unwinplumbing.co.uk/wp-content/uploads/2014/04/DSC00010.jpg
    More Googling reveals it might be called a External Expansion Vessel

    Sorry I cannot be more helpful! Hopefully a plumber can make sense of this!
     
  14. dilalio

    dilalio

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    Nope, that's part of the safety system on a UV and nothing to do with boosting water main. That type of UV is also not directly connected to the DHW it allows for expansion of heated water in the sealed flow and return circuit.
     
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  15. Madrab

    Madrab

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    Yup +1 ... The megaflow has a built in expansion safety system and doesn't come with an external expansion vessel (EV).

    As @dilalio mentions, the red EV is for the sealed central heating system that heats the hot water and has nothing to do with the actual hot water pressure for the shower or anywhere else.
     
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