Diagnosis
It's usually one of three things: a poor battery connection in the remote, the sensor window on the heater being blocked, or the remote's internal circuit getting zapped by a static discharge or a bad battery.
How to Fix It
1) Double-check the battery. Use a name-brand CR2025 battery and ensure the positive (+) side is facing down, towards the circuit board. Clean the battery contacts in the remote with a pencil eraser to remove any corrosion. 2) Check the infrared sensor on the heater's control panel. Wipe it gently with a dry cloth—dust or smudges can block the signal. 3) Stand within 15 feet with a clear line of sight to the heater and try again.
If That Didn't Work
The remote might need a reset. Take the battery out and press every button on the remote a few times to discharge any residual power. Leave the battery out for a full minute. Reinsert the battery and try. Also, test if the remote is emitting a signal by pointing it at your smartphone camera (in selfie mode) and pressing a button—you should see a faint purple light flash in the camera view from the remote's LED.
Heads Up
The heater's control panel can be temporarily 'blind' to the remote if the main unit is in a fault state (like an overheat condition). If the heater isn't responding to its own buttons either, address that primary issue first. Replacement remotes are available, but they sometimes need to be paired—consult for a pairing procedure, which usually involves holding buttons on the heater and remote simultaneously.