Rheem tankless gas water heater always starts on HIGH!

The Tank Rheem tankless gas water heater always starts on HIGH!

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  • #22661
    toysareforboys
    Participant

    We had our failed electric water heater replaced with a Rheem RTGH-84DVLN Tankless water heater a few weeks ago. Couple of issues with it but the main one is:

    When the hot water heater is at rest and even a tiny amount of hot water is requested the hot water heater starts on its highest setting. This is very loud (the hot water heater is located in a noise sensitive area), and a waste of gas and electricity and wear and tear on the machine. When it switches from the highest mode to the lowest mode there is a big air pressure change inside the tankless cabinet which causes the poor quality/flimsy front cover to do a big flex and give out an all mighty THUMP.

    It wouldn’t annoy me so much except that for some reason when any toilet in the house gets flushed it triggers the water heater to fire up! IN HIGH mode, THUMP, low mode, off, all in the period of 3 or 4 seconds. What a waste.

    I called Rheem tech support at 800-432-8373 and spoke with a “senior” technician and he laughed when I asked if we could make it start in the lowest mode. “But it would take an extra few seconds to get the full hot water out of your taps! Why would you want that?”. After that he didn’t seem very helpful and just said “Nope, can’t change that, always starts at 100%.” Yay.

    There’s eight dip switches in this beast and I only know what one of them is for (DIP1#4 to unlock 140f max temp output setting).

    So….. Anyone know what the rest of the dip switches are for? Ideally I would like to DELAY the activation of it by 1 or 2 seconds (to stop the toilet flushes from activating it) as well as make it start always on the lowest mode (i.e. be less aggressive trying to heat the water quickly).

    Thank you for any help or advice you can provide.

    -Jamie M.

    #22665
    Larry Weingarten
    Participant

    Hi: You might run this dip switch question by the installer, who should have a service manual for the heater. Other thoughts that come to mind are to add an expansion tank just upstream of the heater, so using cold water is less likely to reduce pressure in the hot side of things. Also, can a brace be added to the heater door to stop the banging? 😉

    Yours, Larry

    #22670
    toysareforboys
    Participant

    eleent wrote:

    Hi:  You might run this dip switch question by the installer, who should have a service manual for the heater.  Other thoughts that come to mind are to add an expansion tank just upstream of the heater, so using cold water is less likely to reduce pressure in the hot side of things.  Also, can a brace be added to the heater door to stop the banging? 😉

    Yours,  Larry

    Thanks for the reply! I also had another person say that when we cause a big drop in the cold water line (i.e. flush the toilet) that’s what’s causing the hot water trigger. I still don’t understand quite how it’s triggered though, is hot water flowing backwards through the heater causing the trigger??

    I was planning on adding an on demand re-circulation pump under my kitchen sink and I see that Rheem recommends adding an expansion tank to the cold water input line of the water heater so I guess I might kill two birds with one stone if that’ll also solve my flush problem. http://tafb.xxx/Rheem%20recirculation%20pump%20tankless%20diagram%20Piping-Diagrams_MAIN_print.pdf

    There isn’t much room behind the door to put bracing, at least not the top half. I did put a foam block on the main center cover support beam (the silver beam visible running left to right in this pic) to put outward pressure on the cover when we screw it back on, but it seemed to make the problem even worse, there were four parts flexing instead of just the center 🙁

    Another person suggested that the door flex could be caused by an obstructed intake pipe so I did an inspection and the support beam that was holding up the intake pipe broke, so it was pretty much snuffed right out against the snow and ground!!

    I’ve temporarily tied it up to the exhaust pipe so it’s not so close to the ground.

    In reading the installing manual, does the intake pipe need to be so long? The deck is completely open on one end and has lattice covering the one side, I don’t think that counts as an “enclosed” deck?? When I call the installer in the morning I’ll ask him if he can shorten the intake pipe close to the wall. And if he’s got the service manual I’ll photo copy the pages that show any dip switch settings 🙂

    Thanks again for the reply.

    -Jamie M.

    #22697
    toysareforboys
    Participant

    The installers came back and cut the intake pipe way way shorter (about 2ft from the house wall). The water heater is quieter (it doesn’t start as high now) but the door still flaps pretty bad.

    I got the problem fixed with the toilets activating the water heater. Installed a backflow preventer (i.e. check valve) and an expansion tank and no more toilet activation!

    I also took advantage of it starting at pretty high 🙂

    Soooo nice.

    -Jamie M.

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