On average any gas tankless water heater takes around a few minutes to completely heat up the water, however, if you have switched off your heater or have recently installed a new gas water heater then your heater can take up to 45 minutes to warm up the water inside. But all in all, this depends on the type of your heater, its capacity in gallons or BTU but if you have to wait for an hour for hot water to reach your faucet then it is likely that your water heater is faulty. The good thing is that gas water heaters have a faster recovery time as compared to electric heaters but regardless of the type of water heater they never take an hour to heat up water for only minutes.
