Problem...Tankless Water Heater and Occasional Low Water Pressure

kawh707August 14, 2013

Help! We recently got a tankless water heater. We were really happy with it, until we realized that it seems to freak out when the watter pressure drops low. We are on a well and, when watering the gardens, the water will drop low. When the pressure drops, the heater seems to cycle on and off...on and off... constantly for the duration... even though we are not using hot water. The installers came out and installed a valve(?) of some sort which was supposed to cure the problem. However, this evening is heard it cycling on and off again, even though no hot water was being used. Yikes... seems like it will be 1) hard on the heater 2) using a lot of electricity 3) possibly using a lot of propane to heat. (though I'm not sure the gas is going on and off as well.
Anyone know what we need to have done to cure this???

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Sounds like you need a bigger pressure tank for the well.

    Bookmark   August 14, 2013 at 2:51PM
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I used to represent Rinnai in my business. I had this happen with phantom operations and was really puzzled at first. What is happening is you are drawing water from other parts of your domestic system and creating negative pressures in, at least, the area of the water heater. When the pressure neutralizes or goes positive the incoming water is then turning the turbine wheel in the cold water inlet causing the unit to "phantom fire".

I agree that the tank is undersized or the pump isn't putting out the water. It isn't the tankless' fault. It is only reacting to what itis seeing.

    Bookmark   August 14, 2013 at 7:57PM
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My electric tankless unit occasionally activates when there's cold water flow somewhere in the house ... especially when the washer shuts OFF its cold valve after running a spin-spray or rinse fill ... as per Jackfre's explanation above.ÃÂ I hear the relay snap, then it snaps again after about 1 min when the unit deactivates, since there's no hot flow that actually occurs or is maintained. It doesn't cycle on/off repeatedly ... just once on and off.

    Bookmark   August 14, 2013 at 9:02PM
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thanks much for this information. yes, we do need to get a bigger tank for the well.... however, this problem has been solved with a pressure valve near the tank. wish i could tell you more specifics...but i can tell you that the installer tried putting in a valve (he heard that this would cure the problem) and it didn't help at all. when he returned after a few weeks, he decided to call rinnai again, and he talked to the right person. he needed a bigger valve of some sort.... installed it... and it fixed the problem! i'm so happy about this.... and we will work on getting the well in check as soon as po$$ible!

    Bookmark   October 7, 2013 at 1:03AM
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