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Rinnai tankless cycles on when toilets are flushed.

Sibley
Sibley Member Posts: 4
in Domestic Hot Water

Installer changed 1/2" water lines to 3/4" during installation. Everything working fine except when toilets are flushed, tankless unit blower cycles on for a short period of time.

Anyhelp would be appreciated.

Comments

  • bjohnhy
    bjohnhy Member Posts: 58

    Every toilet in house? Does this happen when you turn cold on to bathtub?

    Do you have hot water recirculation? Dedicated recirculation line or a crossover valve that uses cold water line as return?

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,848

    Some type of cross connection between the hot & cold water??

    SuperTech
  • Sibley
    Sibley Member Posts: 4

    Not all toilets, just the downstairs one, and yes, the unit cycles after turning on the cold water for the bath tub.

    No hot water recirc lines and only two mixing valves, one in the downstairs shower and the other is the kitchen sink.

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,636
    edited January 3

    Hi, Do you have check valves in the cold supplies to the mixing valves? Also, have you done a cross connection test? This is where you shut off water supply to the heater and open any hot tap. It should stop flowing in seconds.

    Yours, Larry

    Grallert
  • Slimpickins
    Slimpickins Member Posts: 351

    Yes first check for a cross and make sure you don't have crazy high water pressure.

  • bjohnhy
    bjohnhy Member Posts: 58

    This is a nice instructional:

    https://www.prostarmechanical.com/blog/plumbingcrossover

  • bjohnhy
    bjohnhy Member Posts: 58

    Mixing valves with no checks or without functional checks are a common source for crossover.

  • yellowdog
    yellowdog Member Posts: 204

    Toilet anti-sweat valve causing the cross?

  • Intplm.
    Intplm. Member Posts: 2,318

    Here's a thought. Is the toilet piped with hot water?

    Flush the toilet a half a dozen times or more letting the tank fill each time and then feel the pipe under the tank and the water. Is it hot?

  • hot_rod
    hot_rod Member Posts: 23,816
    https://forum.heatinghelp.com/discussion/comment/1831637#Comment_1831637

    What model mixing valve is installed? An ASSE 1070 comes with check valves. They are required as part of the listing.

    Some valves have dual listings ASSE 1017, point of distribution, and ASSE 1070 point of use. Those models will have two checks in the box also.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sibley
    Sibley Member Posts: 4

    Cross connecton test done to no avail. Followed the instructional link, thanks bjohnhy, and everything seem ok. The hot water is shut off to the washing machine so mixing valve {solenoid} is isolated. Both toilets are confirmed plumbed with cold water as well.

    I will change the cartridges in both the single handled faucets for the shower {MOEN} and the kitchen sink {BLANCO}.

    I appreciate all the assistance.

  • hilltown
    hilltown Member Posts: 47

    sounds like when the cold side valves shutoff, it sends a shock wave thru the unit and turns it on for a second or two. You can try a domestic expansion tank and or a check valve at the unit

    bjohnhy
  • PC7060
    PC7060 Member Posts: 1,521
    edited January 5

    This thread is very similar…

    https://forum.heatinghelp.com/discussion/197306/navien-npe-210a-fan-runs-on-toilet-flush

    bjohnhy
  • Sibley
    Sibley Member Posts: 4

    I thought it was a check valve issue the first time I flushed the toilet or turned on the outside faucet for the hose and the units fan cycled on for a few seconds.

    I contacted the installer and requested a check valve be installed on the cold feed prior to the isolation valve on the unit which he did beause I hadn't paid for the installation yet. That did not solve the problem.

    Could the problem be: 3/4" city water line to house…shutoff valve…city water meter…shutoff valve reducing internal water lines to 1/2" throughout the house…increased to 3/4" ahead of tankless and then reduced back to 1/2" for tie-in ?

  • Kaos
    Kaos Member Posts: 336

    You can try to close the cold water supply to the toilet a bit to reduce the flow there, just enough that it doesn't trigger the flow sensor on the unit. With 1/2" pipes, this had the added benefit of limiting the toilet flush/ scolding while showering issues.

    P.S. A big water pressure improvement with 1/2" setup is to replace the cold water pipe from the meter up to where your cold water starts branching off and to the water heater with 3/4". You can leave the rest 1/2".

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