Navien NHB-055 temp too low

rasortown

Hello, I have a 1-year-old Navien NHB-055 Tankless for hydronic floor heating only, that won't go above 102 deg on the outgoing water, for some reason they installed the "outdoor temperature sensor" inside so in my opinion the unit always thinks it is 70* out and keeps the water at a low temp. Everything I am reading says your water should be between 120- 180 outgoing. Is there any way to override the temperature sensor? I tried unplugging it from the unit but it errors out. I am not even sure if I could run the sensor outside because of how far the unit is from an outside wall and how short the wire is. Or am I wrong about the sensor and something else is going on? Any advice would be super helpful. Thanks a lot

Jamie Hall

Two thoughts -- if the outdoor sensor is inside, it's not going to be much help, is it? I'm not sure what the menu options on that unit are, but in spite of it's not being the best unit for in floor radiant heat, there might be a setting which will override or skip the outdoor sensor. Hopefully someone with more Navien water heater experience will know.

On the temperature, though, two sub thoughts. First, most water heaters won't go over 140 anyway. But the other is you don't want the floor heating to go that high -- 120 should be more than hot enough, unless your installation has very poor coupling. You certainly don't want 180!

rasortown

Thanks for responding and I totally agree that 180 is too high but it should be over 102, when it is really cold (like it gets here in the northern hemisphere) it takes forever to heat the house up. There does seem to be a setting to override but it is buried in the Installer options so I am a little worried to mess with it without some advice. As it is right now I can't set a custom temperature or anything.

GroundUp

102 is a perfect design temp for a radiant floor unless your building envelope and insulation is poor. You should never be "heating the house up" with a radiant floor. Set the thermostat and leave it alone. 50,000 BTU is a small boiler, and at 102 degree SWT it's using all those BTUs anyway. A higher water temp will serve no purpose besides using more fuel and causing bigger temp swings. Either disconnect the ODR sensor or move it outside where it belongs.