Bradford-white water heater wont heat water.the blower motor hums but wont blow.also,pilot light wont light,is this just a safety feature?

I would say your on the right track, a humming motor is most likely a stuck motor, so it tries to run it a bit then shuts off because the blower doesn't spin up. Replacing the blower should get you going again, good job troubleshooting!

It is pretty easy - make sure gas valve is open, change control know to pilot. Press the ignitor a few times and once pilot lights up switch control to warm or hot position.

See instructions by downloading manual for MI-403SF6BN from this site
Bradford White Water Heaters Built to be the best

Sounds like a lack of intake air for combustion.

http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Call Bradford White or installer

Gene
h

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Copy following link to troubleshoot by type of gas control valve:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Bradford White posts service manuals: Both before and after introduction of ICON (Honeywell) gas control valve
http://www.bradfordwhite.com/documentation/residential/gas.asp

Don't forget to clean air intake locate under combustion parts, using instructions in service manual. Or compressed air. Ample air supply will ensure that combustion chamber does not overheat because of slowed venting of hot combustion by-product that will trip the FV system.
And remove heat trap inserts if water pressure has problem or water heater is humming or whistling

Post question on pro water heater forum:
http://www.thetankatwaterheaterrescue.com/forums/forum3/

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

here's what Bradford White lists....
Burner Will Not Ignite
REASON REMEDY Excess primary air Adjust air shutter to reduce air supply -- if supplied No gas Check with utility Dirt in main burner orifice Clean orifice -- check for source of dirt and eliminate Dirt in gas lines Notify utility -- install dirt trap in gas line Venturi clogged Clean -- check for source of trouble and correct Pilot line clogged Clean -- check for source of trouble and correct Main burner line clogged Clean -- check for source of trouble and correct Defective thermocouple lead Replace with new thermocouple lead Defective thermostat Replace Defective magnetic valve Replace entire control Thermostat set too low Turn temperature knob to desired temperature Heater installed in confined space Provide ventilation by use of louvers in wall or door time for a service tech.

If the blower will not run, then the unit will not fire up due to a safety hazard. If it is a capacitor start motor, then you may have to replace the capacitor, otherwise you will have to install a new blower motor. Hope this helps

Check
1 that the pump is working.
2 the overheat thermostat is ok

you may have pusge the air out the gas line best of luck