The address code settings are selected using the manual DIP switches and jumpers on the receiver and thermostat. So that the two devices can communicate with each other on the same frequency. If it used to work and you haven't changed these settings then it should still be OK. You can't accidentally change the RF address, it is done by physically moving the DIP switches & jumpers.
Usually the reason for changing the RF address would be if something else is interfering with your thermostat. What generally happens to make a change necessary, is that a thermostat will switch the receiver 'on' and 'off' as it should, but it also gets switched 'on' and 'off' by something else, usually another Salus in a neighbouring property set to the same RF address (usually both have been left on the factory settings)
However, there's no harm trying changing the address, but you need to set both devices to have the same one. The instructions tell you how to do this, but it is important to follow the instructions to the letter so that every step is carried out and in the right order. There is a link to the instructions
here.
in my desperation I pressed the reset button on both the boiler and the thermostat.
I'm not sure about the boiler reset, but the thermostat reset shouldn't cause a problem other than you loosing the time / temperature settings that you have entered. Even if the boiler was disconnected the receiver should still switch on (green light) when the thermostat tells it to, and that's still not happening.
I did have a power cut before, when a light bulb went and the fuse came out. Maybe that effected the system?
It shouldn't have damaged it even if it lost power. It is would be very unusual for the Central heating to be connected to the same fuse as the lighting anyway, but even if it was and fuse blew, it shouldn't have caused a problem really,......but if that's when it happened, nothing else has changed, and all else has failed to fix it, it's looking a distinct possibility.