The gas meter's diaphragm could be faulty.
It's possible that your hot water system isn't getting enough gas (which can be caused by an under-sized gas bottle).
It's possible that a faulty showerhead or restrictor is preventing a tap from being registered as a 'hot water' tap.
Low hot water pressure could be a problem for your system.
The strainer valve on the cold inlet is clogged.
The thermostat is broken or malfunctioning.
The pilot light may be to blame if water is also coming out at a lower pressure. However, keep in mind that instantaneous units deliver hot water at a lower pressure than storage systems.
Check to see if gas is still flowing to a stovetop or other gas appliance. If it does, the problem isn't with the gas supply; if it doesn't, you've most likely identified the source of the problem. Check your gas valve meter and contact us if there isn't any gas flowing to other appliances.
Double-check that the continuous flow is properly connected to its power source.
If your system has a controller, make sure it's turned on and the temperature is set correctly.