The IPC 2012 section 607 requires that water heaters in residences have mixing/tempering valves set to no more than 110F, and that the aquastat/thermostat on the heater itself set to the same does NOT constitute a complaint alternative (see 607.1.1) nor does local mixing valves at the taps (607.1.2). Even if the installer is required to set it to 110F doesn't mean that you are required to leave it there though. Most local plumbing codes in the US are based on the IPC. In previous versions the section numbers differ, as do some of the specific temperature requirements, but mixing valves on the output of any water heater capable of being set up to 140F or higher storage temps (basically all of them) has been code for at least the last three versions, making it pretty much code everywhere in the US that HAS plumbing codes. Non-compliant installations are grandfathered in, but have to be brought up to code whenever a new water heater is installed.