Saxat från: Remote repair facts
Reduced Operating Range
With proper design, there really shouldn't be anything in a remote control (or the receiver) that degrades with reasonable use (at least in terms of operating distance). However, not all remote controls are properly designed (or manufactured) and there can be other causes for a remote that used to operate reliably from the other end of the house or bounced off the far wall but now won't even respond directly from a few feet away:
*Weak batteries - replace them!
*Dirt, gunk, tobacco smoke or cooking grease residue, and other coatings on the windows of the hand-unit or receiver. Clean thoroughly (but gently) with detergent and water, and alcohol, as required. This may mean INSIDE as well as outside!
*Damaged window in hand-unit or receiver. If someone attempted to clean the window with sandpaper, there could be problems. Remove, replace, or polish the damaged area.
*Weak IR LEDs. Since these are driven hard, it is possible for them to degrade over time. Replace with high intensity IR LEDs from Radio Shack or a real electronics distributor and see if that helps.
*Dried out reservoir capacitor. To drive the IR LEDs requires large peak currents. Sometimes, this depends on the input capacitor fed from the battery and not the battery itself. If this capacitor goes bad, the peak output will be greatly reduced or will be erratic. Test and/or just replace all electrolytic capacitors in the hand-unit.