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Rinnai error code 12 on multiple units

RC4G Member Posts: 4
I have two R94LSi tankless water heaters both exhibiting the same issue. Turning on on a lavatory faucet will cause the heater to throw an "12" error code on initial ignition. Flow rates for the lavatory faucets are all greater than 1.1 GPM (verified on the heater by holding the up arrow button for 2 seconds and then pressing the on/off button.

The 2 Rinnai R94LSi LPG water heaters that are 6 years old. I just purchased the house in January so I have no previous history on how long this problem has been an issue.

Since error code 12 diagnostics all point to a gas pressure/flow problem I had my LPG provider send out a technician to confirm that the 1st stage regulator on my 250 gallon LPG tank (85% full when tested) was working correctly. Test port on the regulator showed more than 12 psi but then he though there might be a problem with the 2psi regulator at the main feed into the house (located about 15 feet from LPG tank) but I think his gauge was suspect / not clibrated. The LPG tech. suggested that I get rid of the 2 psi system and change to a standard 1st stage / 2nd stage LP regulator system instead and scheduled the master plumber they consistently use to come out. The plumber replaced the 2 psi regulator with a 2nd stage LP regulator and eliminated the non-venting 11 WCI regulators in the attic (one dedicated to one of the R94LSI heaters and the other for the manifold system feeding the rest of the house. The only items that are LPG in the house are my kitchen cooktop, fireplace, the two R94LSI water heaters and my LP clothes dryer. The ovens, and central heat are electric. The main feed into the house and to the manifold system is 1".

Converting to the LP 2 stage regulator system did not eliminate my issue however. Hot water to showers, tubs and higher flow kitchen faucets ( => 1.8 GPM) activate either R94LSI just fine, only when a single lower volume lavatory faucet ( 1.1-1.3 GPM) is turned on does either heater immediately show an error code 12.

Dip switches are set correctly on both units (1 on, 7-8 off) and the both units are set for 120 degrees and vent length < 8 '. The firebox is cleaned and the previous owner states he flushed both units every 18 months.

Since min. water flow rate to initially fire either of these units is .4 gpm and the lavatory faucets are pulling almost 3x that I don't believe it is a water flow/pressure issue. Both units fire and run fine with the higher flow rates with a good blue flame visible thru the observation port when active. The kitchen cooktop burner flames are strong/blue even with all 5 burners on high.

The "master plumber" is scratching his head but to be fair he stated up front he is not an expert diagnosing tankless water pump error codes.

Is this a gas pressure setting issue on both heaters? Is calibrating the lo/hi gas pressure settings on the units required at initial installation because I have no way of knowing if the original installer performed this calibration.

Any thoughts how to identify the issue or proceed?


  • rick in Alaska
    rick in Alaska Member Posts: 1,179
    Gotta do a pressure check on low and high fire first, along with inlet pressure. I think low fire is like .77inches and high fire around 2.7, but these numbers should be on the info on the side of the unit.
    Check this first and see what it does.
  • Jack
    Jack Member Posts: 1,045
    With no flow to the unit, in the first bank of dip switches, throw dip switch 7. That is forced low fire. Start flow to the unit and note the gas pressure. Always set low pressure first. You need a good manometer...and know how to use it to do this. Don't "hit and hope". It sounds like your gas pressures may be to high on low fire and it is "blowing out" the flame.
  • RC4G
    RC4G Member Posts: 4
    Thanks for the input.

    I figured we have a hi/lo pressure calibration issue so your responses seem to provide at least some validation for that assumption.

    The only thing about the pressure being too high on the low fire and getting "blown out" wouldn't it also do that when the higher water flow-rate devices (garden tub, shower, hi volume kitchen faucet, etc) are used? In my case those device do not generate the Error 12 code, only lower volume faucets (1.1gpm - 1.3gpm).
  • Jack
    Jack Member Posts: 1,045
    That gas valve will modulate from 10,000-199,000 btu. I suspect it is "catching up" with the pressure gradient as the flow rates increase. Set the low pressure first and then the high. I suspect that both are likely off.
  • RC4G
    RC4G Member Posts: 4
    edited May 2017
    Jack's diagnosis was spot on, the lo pressure settings on both water heaters was hi, 1.2 in/wc where it should be .92.

    Since the "master" plumber who came in and swapped out the 2 psi system with 1st/2nd stage regulators didn't want to touch either tankless heater I decided to set the manifold pressures myself.

    Obtained a nice quality digital manometer from Amazon for $38 to my door:

    Used the Rinnai service manual downloaded from their site and followed instructions exactly to set lo/hi pressures (.92 in/wc / 5.0 in/wc) on both water heaters. Once set correctly, activating hot water on the even the lowest flowing faucet in the house successfully fired the heater with no more Error 12 codes.

    Just wanted to update the thread and say thanks to those who assisted diagnosing the original issue.
  • j a_2
    j a_2 Member Posts: 1,796
    Nice job....
  • BobC
    BobC Member Posts: 5,190
    @RC4G I bought one of those manometers a couple of years ago to verify the gas pressure at the output of my meter. They are well worth the money for occasional use. My only complaint is they could be better damped.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Jack
    Jack Member Posts: 1,045
    Glad it worked out and thanks for posting results. So many times we never hear back from the OP. Get to know the features on the touch pad. You can get a lot of info out of it.
    kcoppj a_2
  • RC4G
    RC4G Member Posts: 4
    I would like to understand all the features but the instructions that came with it read like shampoo instructions (have zero detail).
  • worthydaydream
    worthydaydream Member Posts: 1
    edited February 2019
    I'm not real technical and I know this is an old thread, but hoped my story might help others. I bought a Rinnai and was getting the same error code 12, so I called the installer back. Turns out, the unit wasn't getting enough gas pressure. he ended up replacing my half-inch-gas-pipes with one-inch-gas-pipe. After that, no more error code 12.
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