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Rinnai code 14 problem

I hope that someone can help me with this problem, because it's extremely annoying. I have a Rinnai RC98hpe natural gas, condensing tankless unit that is heating water for our 1500sf, two bath home. I bought it off Ebay for a steal (looks like a customer return that was never put in service) and self-installed. The water heater has worked perfectly for the last couple years except during the winter months when the water supply gets colder. If I open the hot water for the tub on full blast, which is around 5 feet from the heater, then I get a code 14 (the resettable bi-metal switch, not the one-shot fuse). If I open the hot water to the tub gradually, then I don't have this problem. I also get a code 14 if our washing machine, which is around 30 feet from the heater, is set to hot or warm water. I don't get a code 14 if I just open the hot water at the tap full blast or run the dishwasher.

The gas pipe to the heater is sized properly, and I'm getting 7.8 in WC of pressure at the heater. I've set the water pressure to 70 psi. I've flushed the heat exchanger with vinegar, which seems to help temporarily. I can set the forced low fire manifold pressure on the heater just fine, but if I try to set the forced high fire manifold pressure I get a code 14 immediately (this is while the hot taps for the tub and sink are open). Our water is pretty soft, so I don't think it could be scale in the heat exchanger. I also don't see any signs of overheating on the heat exchanger.

I'm thinking I should try to test the temperature at the bi-metal switch as I try to recreate a code 14 (I've read it supposed to pop at 207 F) to make sure it's not malfunctioning. Does anyone else have any ideas about what could be causing this problem. I've tried calling Rinnai, but all they will do is give me the numbers of certified repair techs in the area.


Comments

  • 4Johnpipe
    4Johnpipe Member Posts: 478
    edited November 2015
    You may want to get a certified contractor in to perform tests.
    This link is the tech sheet...
    https://www.rinnai.us/documentation/downloads/U290-663(00)_tech_sheet_RC98HPe_tankless_water_heater.pdf
    LANGAN'S PLUMBING & HEATING LLC
    Considerate People, Considerate Service, Consider It Done!
    732-751-1560
    email: [email protected]
    www.langansplumbing.com
  • 4Johnpipe
    4Johnpipe Member Posts: 478
    Try this one...
    LANGAN'S PLUMBING & HEATING LLC
    Considerate People, Considerate Service, Consider It Done!
    732-751-1560
    email: [email protected]
    www.langansplumbing.com
  • dflippin
    dflippin Member Posts: 2
    Did you ever have any luck fixing this? I am experiencing a similar issue, where I get random code 14's, most of them occur instantly when I turn on the faucet to full. Turn the faucet off, the beeping stops (code 14), turn it back on and it will work most of the time, seems to be very little rhyme or reason to when it want work.
  • taylorjames
    taylorjames Member Posts: 3
    Thermal fuse has been activated due to the high temperature in the combustion chamber and venting. Ensure that there is no blockage in the vent system (lack of the combustion air). Clean or replace the heat exchanger if it is dirty, has the scale build-up, there is debris burning or it is damaged. Increase the water flow if it is too low.
  • dflippin
    dflippin Member Posts: 2
    I'm sorry I haven't gotten back but been very busy and haven't had much time to work on this. With my setup I have a water softener in front of the tankless and I did get to do the descale procedure, I ran vinegar through for over 2 hours and it was clear enough to see the bottom of the bucket afterwards. I am on a well and don't have a lot of water pressure so I powered up the heater while I still had the pump hooked up and it failed with a code 14 on the 2nd try. This code 14 comes in instantly, you hear the woosh of the propane igniting and then almost instantly the code 14 hits, it doesn't have time to get hot never less going over tempature the failure is more frequent that before but when it does work, it works great and you can run it for 30 minutes solid with no problem. This is an external unit so it doesn't have venting. Any ideas or suggestions is greatly appreciated. Thanks!
  • It could be a bad thermal fuse that trips when the temperature differential is too great. Try replacing it.
    Often wrong, never in doubt.