MiCS-4514 sensor issues and confusion

I recently got a MiCS-4514 dual gas sensor and have been trying to get it working to produce useful data.

The board I'm using is the CJMCU-4541 from banggood:

This board has the heater FET, as well as load resistors for the two resistive sensing elements.

When I connect it up to a 5V supply and measure the outputs from the sensors, one is way down at 0,5V, the other is up at 3.9V. This didn't seem right to me since in normal air this should be set up to sit at mid-range voltage level.

I got out my multimeter to start measure resistances, and the sensor resistances look fairly closely balanced with the load resistances on the board, so the output voltages don't make much sense... or perhaps I don't understand the operation correctly.

Beyond that I'm not too sure how I'm supposed to make sense of these readings and turn them into usable ppm values.

Has anyone else had similar issues trying to get this sensor working?