Diagnosis
Weak or dead remote operation is almost always a battery issue, an obstructed sensor on the heater, or the remote's internal contacts being dirty.
How to Fix It
1) Replace the remote's battery (CR2025 coin cell). Even if a battery seems new, try a fresh one from a name brand. 2) Check the infrared receiver window on the heater (a small, dark plastic panel, usually near the control buttons). Wipe it clean with a dry cloth. Make sure there's no direct, bright sunlight or another strong IR source (like another heater) shining on it, which can jam the signal. 3) On the remote, check the battery contacts for corrosion (white/green powder). Clean them with a cotton swab dipped in a little rubbing alcohol and let it dry completely.
If That Didn't Work
Test if the remote is emitting a signal. Use your smartphone's camera (not the selfie cam). Point the remote's LED at the phone camera and press a button. On your phone's screen, you should see the remote's LED light up with a purplish glow. If you don't see any light, the remote is dead. If you see light, but the heater still doesn't respond from a normal distance (over 10 feet), the IR receiver in the heater is likely faulty.
Heads Up
The remote is a convenience, not a safety-critical part. The heater's main controls always take priority. If the remote fails, you can still operate everything manually from the unit. Don't leave the remote where it can be damaged by heat or fall off a table.