Unable to use DHT11 with NodeMCU(esp8266)
The esp8266 boot configuration pins 0, 2, 15 require a pull-up/pull-down  to ensure the required state at boot. The board (NodeMCU in this case) has pull-up resistor on io0 and io2 and a pull-down resistor on pin 15. The MCU pins io0, io2 and io16 are the NodeMCU pin D3, D4 and D8. You can use this pins in the sketch, but only to attach devices which are not in conflict with the required boot state and are not disturbed by the pull-up/pull-down.

NodeMCU and "Wemos D1 R2 and Mini" esp8266 pins and io overview



Serial

RX io1 RX0

TX io3 TX0



boot config pins with pullup or pulldown on board

D3 io0 PULLUP (LOW for boot to flashing mode)

D4 io2 TX1 PULLUP (Serial1 TX. no RX for Serial1)

D8 io15 PULLDOWN (SS pin if esp8266 is SPI slave)



untroubled GPIOs with optional function for I2C or SPI bus:

D1 io5 default pin for I2C SCL

D2 io4 default pin for I2C SCA

D5 io14 SPI CLK

D6 io12 SPI MISO

D7 io13 SPI MOSI



RTC pin for timed deep sleep wake-up (if connected to reset pin)

D0 io16 - optional internal pulldown, internal pullup not available



not useable: Sx pins io 6 to io 11 connect QIO SPI flash memory (in DIO flash mode the 2 QIO pins can be used as gpio) (in a very special setup the SPI bus can be used with other SPI device)

note: most digital IO start as INPUT_PULLUP