On heating the unit go to a three cycle try on the burner then shot down. The blower will come on but the burn will not. Replaced the flame sensor but stayed the same

Sounds like your you may have a dirty pilot assembly if your unit is a direct spark system. Also check ground wires are secure.

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The flame sensor, which is located in front of one of the burner flames is probably oxidized and needs cleaning or replacement. If the unit can't "sense" the flame, it will continue to cycle.

Check out the flame sensor see if it is clean and check the connections .

You need to clean the flame sensor or replace the flame sensor.

Sounds like the unit is triping the limit before the blower comes on. Try puting the fan ON at the thermostat and see how the burners react with a heating call. If they stay on then I would look at the wiring diagram and try and determine what turns the blower on it the heat cycle. is it temperature or time delay through a control board. Hope this helps.

your thermal fuse near the dryer vent opening or blower housing inside the unit,this is a one-shot fuse when it burns out you can't reset it,you need to replace it,then the radiant sensor(senses the flame),high-limit and cycling thermostats located on the burner tube on the dryer,then the boost and secondary gas valve coils located on the units gas valve body near the gas inlet to the burner tube

http://www.vikingrange.com/MEDIA_CustomProductCatalog/m20127_f20254.pdf
Go to this web site. It has a manual on Viking ovens.
Usually, when the set temp is reached, the flame will cycle down to what is called "Minimum Blaze". This is to put heat into the unit at the rate that it leaves the unit. It helps to hold temp rather than cycle off and on. It cycles high when temp goes below set and then cycles down when set temp is reached.

sounds like its not proofing flame. it has a sensor usually like a needle sticks out into the flame that tells the gas valve the flame lit and is burning so its ok to keep sending gas, if its fails to proof flame then burner shuts down, then it tries to relight 3 times then locks out on fail safe. the blower will sometimes run continually once that occurs to highlight a failed condition. every time you reset it will try again 3 times then shut down. lp gas is very dangerous, even i do not work on it as the gas acts like gasoline and lays around. not like natural gas that disperses well. if you see the flame sensor try gently cleaning it with a little emory cloth. also a loose ground can cause this. check tio be sure any green wires are snug , they actually flow volts to ground through the flame on some to proof, thats why no ground no flame. if that fails then the board is most likely problem. change wire for wire , or get generic replacemant and follow directions exactly. good luck.some ignitors act as a flamre proofer as soon as they are done igniting! rarely do they fail to perform both funtions.

1. check indoor wiring.
2 check selector switch.
3 heater not working.check heater eliment also.