CCS811 sensor not working

[Quinn]

I have two sensor: Si7021 and CCS811 connect to board (nRF51 DK). Si7021 work fine. CCS811 always return NRF_DRV_TWI_EVT_ADDRESS_NACK error. Anyone can give me a help?

[awneil]

So the CCS811 is either not (properly) connected to this bus, or is sending a NACK (Negative Acknowledge) when you try to communicate with it.

What debugging have you done to find the source of this problem?

Are you sure that you are sending the correct Slave Address?