Main oven will light but not continue with larger flame and hotter temp?

Very probably

For some reason you thought it wasn't important to give the make and model of the oven - maybe you think we are psychic, I don't know. A quick Google search (that would, incidentally, have given you a more extensive diagnosis) - for the model and the words "flame failure" may well prove fruitful.

You could always check that the flame is actually playing on the flame failure device and has not been misshapen or otherwise prevented from playing properly on the flame failure device, by dirt/burned food etc., in the bottom of the oven.

Anon
September 2016