Hi can you please tell me how can i check that the water heater uses correct amount of gas ?
If you have a gas meter you can time how long it takes the slowest dial to make one revolution. I attached a chart. There will be a rating plate on the water heater that will tell you how many BTU's it is. A tankless can be more complicated than a tank type as it's output will change depending on usage, so you need to open all the water taps to make sure it runs using the highest BTU's.