What's weird is that it used to work. Here in Switzerland i bought it from a company that provides co2 solutions to soda companies. Can you please advise what adapter i might need? Something between the bottle and the regulator?
If it was working with the regulator, and then stopped working. It might be the regulator or the keg disconnects failed. Not that you might need an adapter, I didn't read the OP as was working and suddenly stopped.
Nothing against your intelligence, just because I'd hate for you to go through all this and it be stupid simple mistake. Make sure when your tank is turned on
Do any of the gauges on the regulator indicate pressure is reaching the unit?
If both gauges are showing pressure, the issue is after the regulator. Take off the keg disconnects and open the regulator and see if CO2 is delivered. The disconnect could have gummed up from beer, if it wasn't cleaned completely. If the regulator has a check valve, try removing that from the setup and see if it delivers gas.
If the tank pressure gauge (in line with the tank stem), is not showing any pressure, it would suggest something failing in the regulator/tank connection. I'm not familiar with European gas cylinders. If the regulator/tank was delivering CO2, the regulator must have a pin inside that corresponds to the pin on the tank. Make sure the regulator still has a pin inside and that it has enough tension to depress the tank pin. It could be a broken spring.
If the tank pressure gauge is reading pressure, but the line pressure is zero that might indicate a blown diaphragm. It could also be a regulator diaphragm is blown, check with the regulator manufacturer about getting a repair kit.
