Ktg,

There are a couple of things you need to check:

Did you check the heat and operation of the dryer with the vent off ?

How or what does the flame look like ?
(it should be a large blue flame that extends the full length of the burner inlet tube, with little to no white tipping at the end of the flame).

If you have a weak, discolored flame(mostly orange or white) or short flame, the heat will slowly increase but never cycle the thermostat to turn the burner off.

You have not reached the 300 degree limiter, or it would have opened and you'd have no heat at all.

But you may have a stuck cycling thermostat(155 dgr) and or hi limit thermostat(200dgr).

The cycling thermostat is located on the blower housing,and the hi limit thermostat is on the burner cone.

You can test them with a meter and match, they should read a closed circuit until you warm them with a match, there should be a click and the circuit should open.

Or if you wish, you could replace the parts, if your flame is proper, and go from there.

:) :) :)