Rinnai tankless cycles on when toilets are flushed.

Sibley

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.

bjohnhy

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

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

Sibley

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

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

Slimpickins

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

bjohnhy

This is a nice instructional:

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

bjohnhy

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

yellowdog

Toilet anti-sweat valve causing the cross?

Intplm.

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

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.

Sibley

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

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

PC7060

This thread is very similar…

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

Sibley

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

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".