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The and buttons can also be used to adjust the speaker and ringer volumes (see page 7) Troubleshooting The Celestia 400 must be serviced by trained engineers. NEVER attempt any repairs or adjustments yourself — you could make the problem worse and invalidate the Guarantee. Always make sure your Celestia 400 is fully plugged into the telephone line socket and the mains power socket. If the phone does not ring … . Check that the ringer volume is not set to -0. . Check that the total REN value of a