My old thermostat has two wires and are not labeled or color coded. The Noma thermostats wiring diagram 2-wire heating says to connect into the R 24V and into the W heating relay.
Done this and my furnace won't kick in, tried reversing the two, but to no avail. I have a Gas furnace.

You may have a very old style two wire circuit and your new thermostat requires a permanent 24 volts to operate. In other words you do not have enough wires to keep 24 volts at the thermostat at all times. All your two wires do is activate a relay for heat.

It would seen to me that if Noma gives a 2 wire digagam, it should work on 2 wires. If the furnace won't start up if you just connect the 2 wires, the problem is elsewhgere maybe a blown fuse for the transformer.

If it does, the thermostat may be bad. If I remember correctly, our Heating and cooling expert doesn't like Nomas.