Will not register

Page 26 says you can register 6 handsets. It sounds like there are handsets already registered. De-registering is on the same page.

https://panasonic.ca/viewing/ALL/KX-TG6431/OI/TG6431_PNQX1624YA/TG6431_PNQX1624YA.pdf

..

1. To de-register the orphaned handsets from their old base:
When the orphaned handset says "Connecting..." or "Out of..."
enter *331734 [menu]
and it will soon beep and display "Not registered"

2. To register the new handset to your base:
press the "Handset Locator" button on the base and hold
it until the "in use" light comes on ( ~ 4 seconds ),
then release the button and set the new handset into
the base phone cradle. After ~ 30 seconds it will beep
and display "Handset #" (next in sequence).

3: Note: the base handles a maximum of 12 handsets.

If your system was fully populated ( ie, a handset is
already # 12 ) you will have to clear all the handsets
from the base and re-register them all in sequence.
( it is the only way to 'rescue' the places occupied
by the lost handsets ).

To clear the base of all registrations:

1. Press and hold the the "Handset Locator" button
until the "in use" light lights and then starts to blink
( ~ 10 seconds ), release the button --
then press it again briefly while the "in use" light
is still blinking.

2. The base will beep and all handsets that were registered
will display "Not Registered"

3. Follow the instructions above for each handset
in turn to re-register them:
press "Handset Locator" ~ 4sec ( in-use light on ),
set handset into the base cradle, etc.

The manual is available from: www.manualslib.com
but does not fully describe these procedures.

Good luck !

1. To de-register the orphaned handsets from their old base:
When the orphaned handset says "Connecting..."
enter *331734 [menu]
and it will soon beep and display "Not registered"

2. To register the new handset to your base:
press the "Handset Locator" button on the base and hold
it until the "in use" light comes on ( ~ 4 seconds ),
then release the button and set the new handset into
the base phone cradle. After ~ 30 seconds it will beep
and display "Handset #" (next in sequence).

3: Note: the base handles a maximum of 12 handsets.

If your system was fully populated ( ie, a handset is
already # 12 ) you will have to clear all the handsets
from the base and re-register them all in sequence.
( it is the only way to 'rescue' the places occupied
by the lost handsets ).

To clear the base of all registrations:

1. Press and hold the the "Handset Locator" button
until the "in use" light lights and then starts to blink
( ~ 10 seconds ), release the button --
then press it again briefly while the "in use" light
is still blinking.

2. The base will beep and all handsets that were registered
will display "Not Registered"

3. Follow the instructions above for each handset
in turn to re-register them:
press "Handset Locator" ~ 4sec ( in-use light on ),
set handset into the base cradle, etc.

The manual is available from: www.manualslib.com
but does not fully describe these procedures.

Good luck !

Silent Mode
You can silence the ringers on the base and all handsets for a specific period of time; the answering system answers any incoming calls without playing anything through the speaker.
With the phone in standby, press and hold # on any handset. The phone prompts you to select the number of hours (1 - 9 or Always On) that you want it to stay in silent mode.
To confirm, press # or just wait about 5 seconds. The phone turns on the answering system and displays Silent Mode On on each handset.After the selected number of hours, the phone automatically exits silent mode. To exit silent mode manually, press and hold # again.
If the phone is in silent mode and you turn off the answering system, the phone exits silent mode.
Multihandset Features To use the features in this section, you need at least 2 handsets.
Your base supports a total of 12 cordless handsets: the one that came with the base and up to 11 DCX160 accessory handsets.You must register accessory handsets to the base before using them. (Handsets that came packaged with the base are already registered.)Handsets that aren't registered display a Not Registered message. For registration instructions, see p. 18, or see the accessory handset manual.If a handset was ever registered to a base, you must reset it before it can register to a new base; see p. 18, or see the accessory handset manual.Conference Calling
When an outside call comes in, two handsets can join in a conference call with the outside caller.
To join a call that's already in progress, just press Talk/flash or SpeSpeSpeaker.To leave the conference call, hang up normally; the other handset remains connected to the call.

• Your telephone can accommodate up to four cordless handsets. You can add new handsets (Model E560-2, sold separately) at any time, but each must be registered with the base before use.
• The handset provided with your telephone is automatically registered as Handset 1.
• Additional handsets will be assigned numbers in the order they are registered (2, 3 or 4). You can register a maximum of four handsets.

To de-register all handsets
• Unplug the power supply from the base unit.
• Remove all handsets from the charge cradles and base.
• Plug in the power supply while pressing and holding the HANDSET LOCATOR button.
• Continue pressing HANDSET LOCATOR until the IN USE and CHARGING indicators are lit (this could take up to 10 seconds).
• Release the HANDSET LOCATOR button.
• All handsets will display: ENTER BASE ID: XXXXXXXXXX
Once the base indicators turn off (up to 30 seconds), the handsets have been de-registered from the base, and can now be re-registered.

To re-register a handset:
• Make sure your handset batteries are properly installed and charged.
• Your handset will display "ENTER BASE ID".
• Enter the 15-digit Base ID number from the bottom of the base unit.
• Press SELECT to accept the new code and complete re-registration.

To re-register a handset to a new base unit:
• Make sure your handset batteries are properly installed and charged.
• Unplug the old base unit. Your handset will display "SEARCHING...".
• Install the new base unit by plugging it into an electrical outlet and phone jack.
• Press and hold the SELECT key until the handset displays "ENTER BASE ID".
• Enter the new 15-digit Base ID number from the bottom of the new base unit.
• Press SELECT to accept the new code and complete re-registration. The handset is now registered to the new base.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

Please try the following procedure to register the handset:

1. Place the unregistered handset in the telephone base. If PRESS FIND HS 4 SEC ON BASE does not appear on the handset screen after a few seconds, remove the handset and place it in the telephone base again.
   
2. On the telephone base, press and hold FIND HANDSET for about four seconds (until the red IN USE light on the telephone base turns on) and then release the button. The handset shows PLEASE WAIT... and it takes up to 60 seconds to complete the registration. The handset shows HANDSET X REGISTERED (X represents the handset number assigned) and you hear a beep when the registration completes.

When the registration is complete, the newly registered handset is assigned the next available handset registration number. For instance, if you already have HANDSET 1 and HANDSET 2, the next registered handset will be HANDSET 3

I have same problem

The "END" and "#" key combination can be used for several purposes:

1) If wanting to use an ALREADY REGISTERED HANDSET on an alternate base, and if if the INITIAL BASE isn't available to deregister the handset:

1a) Press "END" + "#" until it for 5+ seconds (wait for it to beep)
1b) Choose the "Base Unavailable" option
1c) That'll deregister the CURRENT HANDSET so that it can be re-registered on ANY base.

2) If a BASE has a handset registered to it which you no longer want registered but the registered handset is missing or broken:

2a) Grab another WORKING handset which is properly REGISTERED to the BASE in question
2b) Press and hold the "END" + "#" key for 5+ seconds (wait for it to beep)
2c) Choose the "Deregister HS" menu option
2d) Pick the REGISTERED HANDSET # to de-register. (Every other registered handset EXCEPT THE ONE YOU'RE ON will appear in the list!)

Short answer:
No. This model of phone can only support 4 handsets. If you need more than that, you will need to have a second base unit.

Detailed answer:
One of my handsets went bad, and I just bought complete DCT748-4 package from a seller on eBay for a very good price. This set was used, but in very good condition. I didn't need the whole set - just one handset - but like I said, it was a good price. Anyway, I began by telling my old base unit to de-register handset #2 (the failed unit). However, I then found that I could not register the "new" handset with my old base unit because it was already registered to the "new" base unit. So, I first had to apply power to the "new" base unit and de-register the handsets. Then, I placed one of the "new" handsets onto my old base unit, and it said "Handset Registering ..." and registered just fine. Just for the fun of it, I placed one of the other spare handsets into my old base unit. It said "Hanset Registering ..." but then it beeped and said "Registration Failed." This is because I already had 4 handsets registered to my base, and the base can not handle a fifth handset.

Some tricks from a helpful Uniden rep:

holding down end+# keys at the same time on the phone for about 10 secs (you will hear a beep) will deregister the handset. If you have a dead handset and want to deregister it from the base, you have to reset the base. unplug the phoneline and power. hold down the "delete message" key, plug power back in. about 10 secs later, you will hear a long beep (theres a short beep upon powerup as well). At this point all handsets are deregistred and you will have to reregister them with the end+# trick. this way when #1 handset is dead, you can make a working one #1 and get the broken one fixed

BTW, this is a woot warranty, not uniden warranty. however the uniden rep gave me the number to the people who refurb (rox0rz!) these. I'll post an update when I finally get ahold of them (and the number if its actually helpful)