I am connecting a 240 volt convection oven using a double pole 30 amp but the oven heats but never reaches full temp. It's a brand new oven.

What is the amp rating of the oven, many are 50 amp that I have seen in the past.

Please we need more information:

Make and model of oven. From the specs page, the Peak or maximum Amperage.

Did you take a meter and verify your voltage at the oven? You verify the voltage by inserting the meter probes as follows:

Back to one vertical slot, red to the other = 240VAC. Black in left vertical slot, red in center = 120 VAC. Black in right vertical slot, red in center = 120 VAC.