Just bought a sentry digital safe at an estate auction. did not have a manual with it. do not have combination. how do i reset combination.

I would speak to a locksmith.

A serial number is not a model number, so difficult to answer such questions with a definite answer. They make so many safes in so many types and sizes. Sentry will give the stock combination for fee and a sworn affidavit that you own the safe, but it may have been changed if it is electronic. If it is electronic, you only need a large rare earth puck magnet to open it. Then you replace the batteries and press the red reset button.

Open it yourself in 5 seconds. Magnet method, bounce method, rubber mallet method, hole in the back and a stick method.

https://www.google.com/search?q=open+sntry+safe+no+tools

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To reset the combination on a Sentry safe, open the door of the safe, delete the existing codes, press the PROG or P key and enter the factory code. Finally, enter a new five-digit number as per individual preference, which is the new user combination.
It is always prudent to reset the combination on a Sentry safe when the door is open because it prevents the user from being locked out. To open the Sentry safe door, type the five-digit factory code given in the owner's manual. This factory code cannot be altered.
To delete the existing codes on newer models of the safe as of 2015, press the P button. Then, type the factory code and follow it up by inputting "00000" into the safe. On older models of the Sentry safe, press the PROG button and type the factory code two times.
After deleting the existing codes, press the PROG or P key and then enter the factory code once again. Within five seconds, type a new five-digit number, which is the new user code. To verify if the user code is working, retype it and then close the door of the safe. The user code is the primary code for opening the safe, and users can reset it as often as they want too

http://www.sentrysafe.com/check-your-safe

There is no default combination. Open it with the key and reset it to your own combination.

https://www.google.com/search?q=Sentry+safe+model+number+G1459C+default+combination

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contact a lock smith he will be able to do a master reset

Check out Barney's Locksmith in Covina, CA. Brian is the owner and there's nuttin he can't fix! Tell him Cin sent ya!

My sentry safe opened when I followed the manual.

If yours is the same as mine (Keypad, fingerprint), press 99, clear, 2004, enter, and it will reset it to factory conditions.

Press: Program 2x, enter a digit user-code (green led remains on), enter the 5 digit user pin (of your choice except 00000). After 5 digits entered, the green LED turns off.

First, has the factory combination been changed? Sentry has the code for the factory combination that they can supply you.

If the factory combination has been changed to something else, then Sentry won't have it.

In that case you need to ask Sentry for a 'reset' code combination. There is (at least) one back door to your safe -- a reset code.

The reset code will not tell you what your combination is, it will simply reset the combination to the factory combination.

You can take it from there.

Now, this isn't as hard as it may sound. There is an actual department that handles this at Sentry because you aren't the only one that cannot open his safe.

They'll want some proof of ownership, some $$ for the service, the safe serial number, and probably a notarized form claiming that the safe is yours.

Get 'hold of Sentry on the web and the rest is just process.

BTW -- this is exactly what the locksmith would do.