If your particular model has a scan feature but the radio will not scan channels, then most likely you need to turn up the squelch control. If the squelch is open for any reason, then the radio is in receive mode and will not scan. Try turning up the squelch.
It is not uncommon for the radio to stop scanning on a particular channel, even if there is no apparent activity. This can happen if there is some kind of local interference on that channel which is causing the squelch to open. This will cause the radio to stop scanning. The solution is to turn up the squelch enough so that the radio scans past the offending channel.