tankless water heater cycling

macawake

I have a new (installed Aug 2023) tankless water heater (Rinnai RE199e) that cycles on and and off very frequently when when it is cold outside, say less then 40 degrees Fahrenheit. we have had the installation company out several times and needless to say it works perfect when they are here and there are no error codes. They seemed to have checked everything and it all checks out, gas pressure is fine, filters are clean and whatever else they can check is good. I can not replicate the problem by turning on my furnace, and other gas appliances thinking it might be gas steal. But I am tired of taking 4 a.m. showers with 20 seconds of hot water then 20 seconds of (ice) cold water repeating over and over. Any ideas?

hot_rod

It turns on even without any faucet running?
Does it have a recirculation pump?

macawake

It doesn't turn on by itself, it only cycles off and on when a hot water tap is on and it is cold outside (we haven't had any freezes yet so not frozen pipes). no recirc pump. We had a previous Rinnai hooked up to the same spot for 15 years with no problems with freezing or weather issues.

Larry Weingarten

Hi, One thing you could do as a test is to also turn on a sink hot tap when you shower. This will increase flow through the heater. If running the extra tap keeps hot water in the shower, you'll be closer to knowing what the problem is.

Yours, Larry

mattmia2

Did they do a combustion analysis? Maybe it is off and the cold air or higher fire tips it to the point it goes out. Did they check the pressures at high fire with all other appliances also firing? Does it get combustion air from outside?

hilltown

Sounds like a flow issue…. Did you check for a faulty fixture cartridge causing cold water to enter the hot line?, perhaps a thermistor sensor reading improper or over heating…
Clean the inlet water screen and your shower head and see if that helps.

hot_rod

Strainer on the tankless plugged?