Power vented water heaters typically have a pilot assembly. This consists of an ignition source and a flame sensor rod. The water heater will begin by inducing a draft, the fan runs. Then proving the draft; a small switch operates with the appropriate amount of pressure or vacuum, depending on the model. The pressure switch is a round plastic unit with a clear plastic tube attached and two wires. Never bypass this switch except for testing purposes only. The unit can overheat, creating carbon monoxide; an odorless gas. When a odor is present it is usually alkalides and not CO2. After proving the vent is clear and the draft is functioning properly, the unit will attempt to fire. With a hot element ignitor, a red glowing rod near the burner, the unit first heats the ignitor. Then turns on the gas valve. If the element glows and the gas turns on but doesn’t ignite then the gas pressure to the burner is typically at fault. Only with a manometer can one determine the gas pressure at the burner. AO Smith is 4.5 inches of pressure. 28 inches is equal to one pound of gas. If this happens and only this symptom, one can light the burner with a long stick type lighter. I would not recommend this approach though. It will only give you heat temporarily and is the pressure is too great or there is a build up of gas, you may only loose your eyebrows and eyelashes. Been there once, won’t go back. If the unit fires but then shuts off after ignition then the flame sensor rod is the culprit. Remove the burner and clean the flame sensor rod, the one with only one wire attached. It will give you a couple days, maybe a week before requiring service. Although I have heard of people having a longer effect using this method. It’s a crap shoot. Be sure to check any gas connections you have loosened with soapy water. If it bubbles then fix a leak. Your safest course of action is to call a professional. Ask him or her a few of what I discussed here. If they can’t answer your questions, then show them the door. There are a few bad eggs ruining the eggnog.
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