Two Bathrooms, Lose Hot Water When The Other Shower Is on

amorphous2111 on 05/06/2024 - 22:06
Last edited 05/06/2024 - 22:07

Hi fellow bargainer,

I am hoping to get some inputs before calling in a plumber. My house has 2 bathroom and use a instant gas hot water. Generally we can only use one shower at a time because whenever we tried to run 2 hot shower at the same time one will lose hot water. This basically happens when other water line is on too, like kitchen sink, dish washer, and not even with hot water (turn on the cold water to the dish washer and we lose hot water in the shower too).

I suspect there is a problem with pressure preventing the hot water line to go to the shower head whenever there is a change in the pressure of the network, but I am not a plumber.

Any idea? Thanks in advance.

Home & Garden Hot Water System

Comments

  • Benoffie on 05/06/2024 - 22:13
    +7

    What's the capacity of the system? Often people cheap out and get the low capacity ones like an Infinity 12 or 16. But really, most houses to deal with multiple outlets should be on a 26.

    To be more precise, a shower uses around 9L/min of water. Times by outlets = flow.

    26L instant system should, theoretically, provide enough for 3 outlets simultaneously with spare.

    Edit - also, it could be the flow rate into the property. However AS has this at 500kpa. But the rate coming in off the main could be an issue.

    By all means, get a plumber/gas fitter out but they should investigate all possibilities

    • JimB on 06/06/2024 - 09:31
      +1

      I have a similar issue, I reckon it has to do with the 500kpa water pressure limit and the fact hot water has to travel via the solar hot water to the tank and then the instant system.

      Cold water is ok but hot water has less flow. I have a 26L system.

  • sumyungguy on 05/06/2024 - 22:15
    +1

    What make/model HWS do you have? As already posted above by @Benoffie

  • Stewardo on 05/06/2024 - 22:42
    +1

    Modern Australian taps have a limiter of 9ltrs per minute.
    So if you don’t have strong water pressure, a small diameter gas pipe, a 16ltr per minute HWS, multiple taps open, or mineral build up in your taps, your going to have a combination that will give you luke warm water.

  • MS Paint on 05/06/2024 - 23:46
    +3

    Sounds like your system is suffering from dihydrogen monoxide pressure limitations.

  • Fysh on 06/06/2024 - 00:56
    +1

    Is there a thermo valve ? The gas system might be turning on extra hot due to demand and the valve shuts off as its to hot

  • Dollar General on 06/06/2024 - 08:24

    Just do everything in the shower like Kramer

  • Youfah Mizzum on 06/06/2024 - 08:55
    +1

    Similar situation in my house a few months ago.
    And had odd fluctuating pressure too.

    Plumber came out and replaced the pressure valve near the meter out the front.
    One of these. Now we have good pressure in the house & can have 2 showers at once. I'm 99% sure this would solve your issue.
    https://www.reece.com.au/product/zurn-wilkins-20mm-pressure-…

  • Euphemistic on 06/06/2024 - 09:00
    +3

    Not surprising. Pretty much every house ive stayed in has the same issue. Theres only so much hot water you can pull through the system. Normally, one tap only.

    Its a great way to get someone out of the shower if theyve been in too long. Just go and turn another hot tap on and off full blast. Theyll struggle to keep up with the change in temps and give up. Also potential for them to chase you round the house dripping wet and naked.

    • MS Paint on 06/06/2024 - 10:13
      +1

      I saw that video recently.

  • JIMB0 on 06/06/2024 - 09:18

    I have no problems running 2 showers from a gas storage unit.

  • CheapukeeSkate on 06/06/2024 - 09:27
    +1

    Ahhh this one. Do you have a restrictive low-flow shower head or hose?

    What happens is the cold water effectively has slightly higher pressure as the hot. Thats fine when both are going to ambient room pressure and you adjust the valve positions on each to get the right flow from each, balance the pressures and the right temperature (human sets temperature).

    What happens I think:
    1. Turn on both showers.
    2. Shower 1 with the cold water has low pressure hot pipe (the how water is leaving shower 2 dropping the pressure). The cold pipe flows up the hot pipe on this one.
    3. Shower 2 with the hotter water is getting some cold from cold pipe and mixed hot+cold out of its hot pipe.

    A MS paint would be helpful (I might draw one later).

    A couple of ways to solve it. 1 would be remove the low-flow shower hose/restriction. Makes sure all the hot/cold comes OUT at the fixture rather than mixing and flowing around your hot pipes.

    1. Inline to each shower - put a non-return valve on the hot water pipe. Usually its the hot that is lower pressure so only need that one.

    2. Some fancy valves like they use in USA plumbing that can self-regulate pressures. However here I've never seen something like this sold. We seem to be the backwater of this stuff. No safety really implemented here. See this- does anyone know if these are available here in Australia? https://www.youtube.com/watch?v=4IjXXohWaOQ&ab_channel=ThisO…

    • amorphous2111 on 06/06/2024 - 15:09

      Thank you, I think you are right. It is somewhat a pressure issue rather than the hot water itself. I will try the simplest solution first, change the shower head as I can see that they are the type of flow limitting shower head (8L/m).

      • sumyungguy on 06/06/2024 - 15:10

        Are you certain your HWS has an adequate flow rate? Instant gas systems vary widely and are inherently low-flow; e.g Bosch Hydropower 16H only services one bathroom. Changing your shower head may achieve only a cosmetic improvement to your bathroom.

        • amorphous2111 on 06/06/2024 - 20:23

          my HWS is 20L Rinnai. It was a replacement for an old Bosch when I bought the house, using the same gas pipe. The plumber said it is adequate for our 2 bathrooms.

          • sumyungguy on 06/06/2024 - 20:30

            @amorphous2111: Infinity 20 is ideal for one bathroom and can service two bathrooms only in warmer climates where the cold supply temperature is higher. You probably need a 32 to comfortably service two bathrooms assuming you're in Adelaide. You may have noticed acceptable performance through the summer?

    • lgacb08 on 07/06/2024 - 04:17
      -1

      Mate, your explanation doesn't make sense, his 20l hws definitely underspec for the house, at least 26l flow rate is needed. Contrary to your belief it is very hard for cold water to run back to the hot line because none of those mixer would pass standards here, unless you had some dodgy plumber buying things of aliexpress. Pressure at both incoming ends of the mixer will always be greater than the outlet regardless of how many mixers open, cross flow between hot and cold line will not happen.

  • amorphous2111 on 08/06/2024 - 16:46
    +1

    Just to update: I changed the old shower head and it seems to solve the problem. Both bathrooms are running with hot water now. Thanks for all the suggestions.

    • CheapukeeSkate on 13/06/2024 - 14:08

      Awesome to hear Amorphous. Glad the simple solution worked. The gold standard will be non-return valves on the input to each shower, but if its working don't fix it more than it needs to.

      Most of your outlets are rated to maximum 7.5l/m, so two showers running full hot are well within your 20l/m unit. Don't worry while its working your plumber got it right in the first place.

  • amorphous2111 on 13/06/2024 - 18:48

    Yes many thanks for your input. I did notice that when other open water and I have shower, the water temp and flow are still changing but I can readjust the hot and cold tap to bring it back to normal. Before once it happened there is no way to adjust, water just turned cold no matter how I tried to change the tap.

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