An E1 is directly related to an issue involving your gas supply.
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If you are getting an E1 error code, first verify that your water heater is the correct gas type. On the right side of the water heater, there is a plate that specifies LP for Liquid Propane or NG for Natural Gas. This should match the type of gas that is being supplied. If this matches, verify that your installer checked to make sure that the gas is the correct pressure for your 45H/HI. The pressure needed for this model is 8-11 inches of water column for Liquid Propane and 4-6 inches of water column for Natural Gas. Also, make sure your installer used a regulator capable of delivering the proper gas flow needed for the 160,000BTU 45H/HI. Next, verify that your gas supply is turned on. Lastly, after doing all of this, make sure that you are not out of gas.
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Can you hear the water heater trying to ignite? In a proper ignition sequence, the fan will come on, the display will show ground water temperature, and you will hear a series of fast, high pitched clicking followed by a few lower pitched clicks which are noticeably slower. It should go through this sequence twice if it does not ignite.