DHT22 and Nano Failing to Read

I have an interesting problem that I cannot get to the bottom of regarding DHT22.

I had been running a temperature based project over winter: check the temperature every minute and turn a heater on if it drops below a threshold value; turn the heater off when it goes above. Record values to an SD card. Use an RTC for timing. Works as planned and did so for four months, with me extracting the data from the card once per month.

I don't need that particular project in the summer and so utilised the components on another project, but have run into a problem where the Nano fails to read from the sensor. I have now stripped the project down to the Nano and the DHT on a breadboard, and am using the DHTtester library example sketch to test it. I am using the Adafruit Unified Sensor library (same as for the earlier winter project).

-Wiring continuity checked (it's only three wires)
-breadboard continuity checked
-Nano to breadboard continuity checked

I have run other sketches on this Nano with no problems
I have had this DHT working with an Uno with no problems
I have tried other DHTs, which also work with the Uno, but the Nano still fails to read
I have tried other Nanos and all failed to read

I have tried adding a line to the sketch to read the data pin while the DHT is still connected, and get results that vary if I apply hot/cold air to the DHT. Unfortunately, I do not know what the readings mean, or indeed whether or not they are meaningful, which is why I am using a library in the first place. I just wanted to check if the line was 'seeing' anything. I have some DHTs with a resistor and some without, but that seems to make no difference.

I wonder if anyone has experience of a similar problem or can even suggest solutions?

I have tried other DHTs, which also work with the Uno, but the Nano still fails to read
I have tried other Nanos and all failed to read

Post your code and post a wiring diagram for the UNO and Nano case! Just to assure: Nano means Arduino Nano and not any of the newer boards that also have "Nano" in the name, doesn't it?