Instantaneous Hot Water Service Works Fine When The Gas Stove Is on? Intermittent Failure When Not. Any Ideas?

tunzafun001 on 07/09/2023 - 12:05

Got a Rinnai Infinity instant gas HWS.

Recently started cutting out intermittently (with a 12 coming up on the controller).

Checked the service manual. A code 12 refers to a flame issue. Sure enough it would ignite at start up, then when it normally reduces back to a couple of burners (as it only needs to get to 42C), it would cut out completely.

I checked / cleaned the flame rod and igniter. They are all good. Pulled out and cleaned the burner assembly with no change.

So then checked to see what happens with the stove on. The gas burner drops just a little when the hotwater starts, then goes back up once running.

HOWEVER…this is the weird bit. The HWS works perfectly when the stove is on, but wont run, or intermittently works when the stove is off.

I repeated this about 50 times just to check it wasn't a coincedence.

I'd expect normally the issue would be too low gas pressure, but the whole burner lights fine, but goes out when it drops back to a single burner. So maybe an over pressure issue, but the gas stove looks normal, and does drop when the HWS comes on (which seems like a low pressure issue).

Any help would be greatly appreciated.

Thanks

Electrical & Electronics Hot Water System

Comments

  • try2bhelpful on 07/09/2023 - 12:28
    +4

    Call in a professional and stop trying to DYI with gas.

    • MS Paint on 07/09/2023 - 13:06
      +3

      Do Yourself In?

    • tunzafun001 on 07/09/2023 - 13:47
      +6

      Rang around…professionals simply say "just replace it with a new one".

      Got the same advice for my Fujitsu ducted aircon "boards dead, not worth replacing…new one $9k fitted"…

      Ended up fixing that with a couple of caps and a triac for just under $5!

      I think this just needs the regulator "re tuned", or maybe the solenoid in the gas control/ modulating valve is on the way out.

      Never looked at a HWS before yesterday, but they aren't that complicated. I'm sure someone has seen this issue 1000x

  • djones145 on 07/09/2023 - 12:42
    +1

    professional time. it does sound like the stove gas line is connected to the hot water. is the hot water system further away from the stove. it might be pressure is not enough to reach the hot water system but when the gas stove u improves the pressure

    • tunzafun001 on 07/09/2023 - 13:50

      Thanks, but I thought the opposite would be true (ie. too much pressure) as it only runs when the stove is on. So perhaps a solenoid doesn't have the strength anymore to open against the pressure.

      Alternatively, perhaps the incoming gas regulator is iffy, and once a higher volume of gas is required down the line, it opens up more and the pressure rises. Never had the to deal with this before. Guess that would be the gas retailer/ suppliers issue?

  • PensionerXXL on 07/09/2023 - 13:37
    +2

    try shorten the pipe with an angle grinder, make sure to tig weld back up tight once done

    • MS Paint on 07/09/2023 - 13:42
      +3

      Post the Facebook Livestream link here first.

    • tunzafun001 on 07/09/2023 - 13:51

      Good Darwinian test.. Hard pass from me!

    • GordonD on 07/09/2023 - 14:44
      +1

      Had a guy renting next door to me who didn't pay his gas bill. The gas company couldn't get in to cut him off at the meter because he grew marijuana and had raised and secured the fences. One morning there was an excavator working on the footpath, went out to ask them what they were doing, and they said they were cutting off his supply by turning off everyone's gas, digging up the pipe supplying his house, and cutting and plugging it. He moved out, new owner bought the place, and asked me why the stove and hot water didn't work. Next thing out comes another work crew, excavator digs up the pipe, repairs it. It cost someone a fortune.

      • tunzafun001 on 07/09/2023 - 16:12

        Apparently this is the way when you want to disconnect your gas and go full electric. They charge a fortune to have it disconnected… but if you don't pay your bill…then they disconnect it.

  • ESEMCE on 07/09/2023 - 13:51

    Only thing I can think is that there's a flake of rust (or other foreign body) blocking the gas pipe..
    When gas flow is high enough, it pivots like a butterfly valve to allow flow, but when flow is lower, there's not enough pressure to "open the valve", so the HWS flames out.

    • tunzafun001 on 07/09/2023 - 14:02

      But it's the opposite, it only works perfect when the stove is on as well, so suggests that it only runs when there is less flow available.

      Works intermittent when the stove is off. Wondering if one of the solenoids is getting tired and is struggling to work against full pressure.

      I opened up the gas modulating valve. It is 2 chambers with a solenoid valve on each (default closed).
      When it first ignites, both chambers are open. When it's at temp, one side closes. It is at this switching point it goes out (unless the stove is on, then it keeps going). So maybe it can't open enough against full pressure.

      Actually, the solenoids look the same on both sides of the modulating valve. Wonder what would happen if I swapped them (as one side would have only done a fraction of the work as the other - ie it only opens for first ignition and when above 55C, so a few seconds each time). Could either swap the order of the problem..or maybe the secondary side will open enough to keep going. Or I might be way off… so strange that it runs perfectly when the gas stove is on.

      • ESEMCE on 07/09/2023 - 14:19

        But it's the opposite, it only works perfect when the stove is on as well, so suggests that it only runs when there is less flow available.

        Depends… If the "blockage" is between the stove and the meter, then the flow to the stove would be in addition to the flow to the HWS, therefore flow would be higher at this point of the pipe with both operating.

        • tunzafun001 on 07/09/2023 - 14:23

          Ok, cheers for this.
          So we could have a higher total flow, but less pressure situation (at the HWS)?

          Sounds like I need someone to check the pressure at both the incoming regulator and the HWS. There is a pressure test point on the unit. So it's definitely doable.

          Now to find a professional who will actually do it…

      • Transient on 07/09/2023 - 22:21

        If you know what you are doing then you could swap the pipes around, in which case the HWS should work properly and the stove should not. If still fails, then there could be a blockage between valve and HWS or valve needs replacing.

  • GordonD on 07/09/2023 - 14:36
    +4

    Pressure regulator fault.

    The gas main is at a high pressure. There is a regulator attached to the meter that reduces the pressure for appliances in the house. Its not working properly at low flows.

    Get onto your gas supplier.

    • tunzafun001 on 07/09/2023 - 20:37

      Top of the chain in Australia…pretty sad isnt it

  • vince088 on 07/09/2023 - 18:41

    how old is the system?

    • tunzafun001 on 07/09/2023 - 20:48

      Coming up on 20 years. Most would say its at the end of its life. But it's a high capacity '24' unit that has been been supplying one person 90% of its life. So just taking it easy at 1/3 output max. Everything I looked at internally still looks brand new (burners, jets, turbine, o rings in manifold / modulating valve). No corrosion in boiler. Impressive construction from the Japanese built Rinnai.
      Hot water unit at our old place was just over 30 years old and still working well.

      • vince088 on 07/09/2023 - 22:28

        wow. my house had a solar hot water system for 11 years when it broke, now I have continuous gas Rinnai system.

        I think 20 years its time for an upgrade :)

        • tunzafun001 on 08/09/2023 - 01:39

          11 years, that's bad. But Im guessing you didnt replace the anode? Or maybe the TPR valve was stuck, so overheated (solar heaters easily go over 80C in summer and crack the inside of the tank if the release valves dont work). What brand was it?

          As for an upgrade, the new units are still exactly the same tech.

  • tunzafun001 on 08/09/2023 - 12:46
    +5

    Just thought I'd report back to wrap up in case anyone else experiences this.

    @GordonD seems to be on the money. Gas company came out today and replaced the incoming regulator. Seems to be all working now.

    If nothing else, I know have a good understanding of how these things works, and at 20 years old…the Rinnai still looks amazing internally.

    • moar bargains on 08/09/2023 - 14:50
      +1

      Chalk up another win for Ozbargain. You should ring all the gas fitters you originally rang and tell them how to fix it for next time ;)

      • tunzafun001 on 08/09/2023 - 15:28
        +2

        Meh…its the norm these days. Bin / replace ..then work back from there.

        *in case there are any gramma police around… I apologise for my previous comment… *now (can't edit it now…it is what it is)

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