Rinnai 1004 - Temp on thermostat reads 10 deg cooler than actual, keeps running

The location of the sensor needs to be higher but my yellow wire would only pull out a couple of inches.
Turn off power to unit and remove front panel. Two screws near top/sides. Top of panel pulls out (unplug wire connector to indicator lights) and lifts off bottom tangs. Now you will see a coil of yellow wire inside unit. Remove the wire tie and you'll have enough yellow wire to locate the sensor well above the heater.

Make sure there is no cold air at the location of sensor. My unit is located on a out side wall and under the floor is not insulated therefor the unit runs until the floor is up to temp. This unis works fantastic but should be able to adapt nto a wall thermostat.

Behind the unit near the floor level, is a yellow wire with a black bulb at the end. This is the actual sensor for returning air. If there is cool air infiltrating the area where it is located, it will keep the unit running until the return air reaches temperature. You could also have a bad sensor but highly unlikely. Make sure there is no air infiltration influencing the sensor. Also, you can unclip the sensor and pull out a few more inches of wire to locate it higher up away from the floor. Tie it up with a wire tie.

Rinnai it testing a remote thermostat but as of yet, there is no plans to offer one.

Had just purchased and installed the 1004FA to my garage which we are in the middle of converting to a play room. I must say that the unit operates fine with the exception that the unit registers ~ 7 deg lower that the actual room temp. I then came to a solution of moving the thermistor... cut and stripped the yellow wire and respliced the thermister to about 8 feet away on the same wall. Now the unit opererates fine and shuts down when the set temp is met. It was easy since the walls are open and wiring is hidden.

Tried to connect a programmable thermostat but its a no go. The heater does not like when the thermister is in an open condition and the main readout on the units control bourd blinks that there is a problem with the thermister. I'd like Rinnai to come out with an adapter for the unit to operate on a programable thermostat it would be a huge plus.

Here is a link for the owners manual.

http://rinnai.us/Rinnai/FileLibrary/DealerResources/DocumentsLibrary/WallFurnacesDirectVentMainHeatSource/RHFE1004FA/GeneralInformation/rhfe-1004famanual_0.pdf.aspx

The temp sensor on all Rinnai heaters are a yellow wire with a black bulb at the end of it. It measures the air behind the unit flowing through it. It is coiled up so that if necessary, it can be relocated outside of the chassis. This is a common problem with poor insulation in walls or poor installation. If the vent kit isn't sealed properly, cold air from the outside will cool the air behind the unit. Try moving the sensor to just outside the unit through the grates on the side, or make sure the vent kit is installed properly. It is a varible resistor, and VERY rarely fails. No, an external thermostat can't be installed since it measure resistance, and doesn't use a normal 24volt system to switch the heater on and off. If you could find a way to hook an external thermostat to the unit, you would undo what makes this unit so great. Self modulating heat control allows for more accurate temp control, and energy savings. The last thing you want is this unit turning on and off at high fire only.

Check out the LUX PSP300 outlet programmable thermostat. This thermostat is plugged into the electric outlet, and the Rinnai is then plugged into the thermostat.The LUX is a full featured thermostat that includes an adjustment of +/= 5degrees F for its base temp reading.It controls the appliance by cutting power. When the Rinnai 1004 powers back up after power interuption it will be set at its default temp setting of 70 degrees F. For most applications this works great as the location of the temp sensor on the Rinnai means you should not need a setting above 70 degrees F.I purchased mine from efi.org for $45.00. Hope this helps......