Is the model number you have quoted the actual model of the water heater or the gas control valve on the front of it – seems like the correct numbers for the gas valve is all.
In any case the input consumption gas be proven by utilising the test dial on the gas meter after shutting down everything else using gas. Measure the volume of gas consumed, the time of the test period, know the calorific value of the gas being used and it can be easily calculated.
As to the efficiency of the water heater with sufficient data provided that too can be calculated fundamentaly.
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians