Hi again and thanks for that information.
From what you describe, you MAY have more than one issue, so let me walk through the possibilities..
First, if the handset batteries have not been REPLACED (with NEW) in the 3-4 year time you have owned these, then that could cause this type of issue. So replacing the batteries in the failing handset would be one of the things I would do - if necessary. This is because "weak" batteries (even if they show that they are fully charged) can decrease the range of the handset, and make it more sensitive to interference.
Next, I would gather ALL of the handsets together in a single room, along with the MAIN base unit, and then "reset" the system. This will allow us to TEST if the handset in question is still "registered" to the main base unit and if it WILL find and communicate with the main base unit of the system when it is "close by". I have the reset procedure I use shown below.Cordless system "reset" procedure.
This is done by following the steps below.
1) Remove the batteries from ALL
handsets in the system.
2) Remove the phone cord from the main base unit AND
the phone jack in the wall.
3) Remove the AC power adapter plug from the main base unit AND
remove the AC adapter from the power outlet.
4) WAIT 15 minutes
. This allows any "stuck" conditions in the components to clear.
the batteries in all handsets.
the phone cord between the main base and the phone jack in the wall.
the AC power adapter plug in the main base unit and then plug the AC adapter into the wall power outlet.
8) Wait 30-60 seconds
for the system to reinitialize.
each handset for proper function.
each function of the main base unit (answering system, caller id, etc.).
Now if the handset still works properly when near the main base unit, then it would be time to see "how far away" the handset would still work AND if there is some "interference" causing the handset to "disconnect" for the main base unit. That will take some experimentation by using the handset and then moving around to different locations in your home - to TEST when & where the handset disconnects. If this happens in a particular room or location, then we must look around in that location to find out what is causing this disconnect. It could be some other piece of electronic or electrical equipment, or just the distance from the main base unit.
As a point of reference about the terms I'm using, I have also included a system diagram (below) showing the terms I use when referring to the "Main Base Unit", the "Handset(s)", and the "Charger(s)".
Please let me know if you can try these things and the results when you do.
Best Regards, XXXXX XXXXX(im)