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Erratic instantaneous gas HWS and water saving shower heads

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  1. #1
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    Default Erratic instantaneous gas HWS and water saving shower heads

    Hi gurus,

    I've recently moved into a house with instantaneous gas HWS and experience very erratic hot water from the showers. Basically the water gets to a hot temperature but then goes cold a few minutes later. I then have to turn the cold water off and wait for the hot water to come back. I've read online and spoken to the AGL Energy Shop about this issue and they mention water-saving shower heads being a problem due to the low flow rate. The way I understand it the HWS needs a certain flow rate to trigger the gas heater. I have 2 shower heads in the house and both behave erratically, I think one of them has a lower flow rate than the other.

    Is this a common issue? Does anyone know what flow rate is required through the HWS? Doing a bit of research and it seems all shower heads are either 9l/min or 7.5 l/min. I think I must have one of each since both act erratically.

    Does anyone know of a brand of shower head that has a higher flow rate than 9l/min?

  2. #2
    Senior Stinkologist Sir Stinkalot's Avatar
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    Ours does this every now and again if the flow is low ..... I too find it is fixed by turning off the shower and starting again. Typically with ours we program the water temperature to close to what we want the final shower temperature to be (typically 45 deg but can go up a little in winter) and then do not use any cold water at all. This seems to keep the flow sufficient to prevent the HWS from cutting out.
    Licence to drill!

  3. #3
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    Quote Originally Posted by TheOtherLeft View Post
    Hi gurus,

    I've recently moved into a house with instantaneous gas HWS and experience very erratic hot water from the showers. Basically the water gets to a hot temperature but then goes cold a few minutes later. I then have to turn the cold water off and wait for the hot water to come back. I've read online and spoken to the AGL Energy Shop about this issue and they mention water-saving shower heads being a problem due to the low flow rate. The way I understand it the HWS needs a certain flow rate to trigger the gas heater. I have 2 shower heads in the house and both behave erratically, I think one of them has a lower flow rate than the other.

    Is this a common issue? Does anyone know what flow rate is required through the HWS? Doing a bit of research and it seems all shower heads are either 9l/min or 7.5 l/min. I think I must have one of each since both act erratically.

    Does anyone know of a brand of shower head that has a higher flow rate than 9l/min?
    Instantaneous or continuous flow hws. It actually makes a big difference.
    But probably the restrictor in the showerhead.

  4. #4
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    It's a Rinnai Infinity 26, which is a Continuous low HWS

  5. #5
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    The Rinnai 26 wont ignite with less than 3l per minute, Still sounds like the showerhead should be modified.

  6. #6
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    Most people do not understand the principles of hot water verses cold water, especially in showers.

    The hot water tap should be turned fully on until the hot comes through, then, while the hot tap stays fully open, the cold tap is turned on enough to bring the water temperature to the required level.

    And as Plum said, the shower usually needs to be modified to allow more water flow.

  7. #7
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    Quote Originally Posted by cyclic View Post
    The hot water tap should be turned fully on until the hot comes through, then, while the hot tap stays fully open, the cold tap is turned on enough to bring the water temperature to the required level.
    That is how I run my showers - hot first then cold.

  8. #8
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    Quote Originally Posted by TheOtherLeft View Post
    That is how I run my showers - hot first then cold.
    That's good.

    Another thing which will impact on the hot supply/flow is poor cold supply caused by old or incorrect size pipes.

  9. #9
    Old Chippy 6K
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    I never use cold with our Rinnai - just set the temp for shower (39-43) or dishwashing (50-55) or whatever and turn the hot on full.
    Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.

  10. #10
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    Quote Originally Posted by Bloss View Post
    I never use cold with our Rinnai - just set the temp for shower (39-43) or dishwashing (50-55) or whatever and turn the hot on full.
    What I have now, less waiting for the hot shower as well as you don't need to wait the extra time for fully heated water

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