Ao Smith Gas Water Heater Manual

Why You're Looking at This Manual Right Now

You probably have a gas water heater that is acting up, or you just got one installed and need to figure out what all the switches and dials actually do. The A.O. Smith manual covers a lot of ground because they make dozens of models. Some are 30-gallon point-of-use units for a bathroom sink. Others are 50-gallon atmospheric vent heaters for a whole house. The differences matter, which is why you should not skip the first few pages of any manual you pull up. The official manuals are free on their website, but the direct link changes depending on whether you are looking for a residential or commercial unit, and whether it is a newer electronic ignition model or an older standing pilot design. The model number plate is right on the jacket, usually near the top. It looks something like GE-30T4N or GMHA-50-DV, depending on the series. Write that down before you search, because the search filters on their site are not particularly helpful if you do not already know the exact series code. The manual for a power-vented unit will not help you troubleshoot a direct-vent model, even though both are gas water heaters from the same company. I wasted about twenty minutes on a dead end last year because I grabbed the PDF for the wrong series. The part numbers inside the manual did not match my unit at all. Once I went back and pulled the correct model tag, the right manual came up in about thirty seconds. Most A.O. Smith residential gas water heaters use one of two thermostat systems. There is the older style with a simple gas valve and a thermocouple that you light with a match through the access panel. Then there is the newer electronic ignition models that have a control board with LEDs for fault codes. The troubleshooting approach is completely different between those two systems. If your heater has a circuit board with lights, you do not need a manual for pilot light troubleshooting because there is no pilot light. The manual tells you which LED blink pattern corresponds to which error. A three-blink fault on an A.O. Smith electronic ignition unit usually means the pressure switch is not closing. A five-blink pattern often points to an open thermocouple circuit. You can reset these by turning the power off at the breaker for about thirty seconds and then back on, but if the fault clears and comes back immediately, you need to look at the actual component rather than blame the board.

The thermostats on these units are also worth understanding before you start turning knobs. A.O. Smith typically sets the factory temperature to around 120 degrees Fahrenheit, which is the standard recommendation for preventing scalding and reducing standby heat loss. If you need hotter water for a dishwasher without an internal heater, you can raise it, but anything above 140 degrees requires a mixing valve if you have young children or elderly people in the house. I had a homeowner call me once because his water was lukewarm after he turned the dial all the way down to save energy. He had dropped it to 90 degrees. The water was technically safe but basically pointless for laundry or hand-washing dishes. Set it back to 120 and let the tank do its job. One thing most people miss in the manual is the anode rod section. A.O. Smith includes a sacrificial anode in nearly all their residential tank models, and it is usually a magnesium rod unless you specifically ordered an aluminum one for hard water areas. The manual mentions replacing it every three to five years, which is honestly optimistic if you have average municipal water. In my experience, a magnesium anode in a hard-water area will look like a rusted sponge after about four years. The tank itself often lasts another five to seven years after the anode is spent because the steel starts corroding from the inside out. I replaced an anode rod on a twelve-year-old A.O. Smith GMHA-50 unit last spring and the rod was basically gone. Just a thin wire core left wrapped in scale. The tank still held water, but replacing that anode was a band-aid at best. The corrosion had already started eating the bottom of the tank. I told the homeowner to budget for a replacement within the next couple of years rather than trying to patch it. The gas valve adjustment is another area where the manual is somewhat vague. A.O. Smith valves, particularly the Hubbell-style valves they use on many residential models, have a flame adjustment screw and a manometer port. The manual tells you to set the flame to a steady blue color with no lifting from the orifice. That is correct but not detailed enough for someone who does not do this regularly. You want the flame to cover about two-thirds of the thermocouple tip when the pilot is lit. If the flame is too small, the thermocouple will not generate enough millivoltage to keep the gas valve open, and the pilot will walk off. I spent an afternoon on a job where the pilot kept extinguishing after a power flicker. The manual suggested checking the thermocouple seating and replacing it if damaged. It was both. The thermocouple was fine but the flame was not reaching it properly because the orifice had a bit of debris in it. A quick compression-air blast cleared it and the pilot stayed lit ever since. The manual never mentions cleaning the pilot orifice as a troubleshooting step, which is a gap I have found in several A.O. Smith manuals over the years.

Condensation issues are worth addressing if your unit is in an unconditioned space like a garage or crawlspace. A.O. Smith heaters do not produce condensation during normal operation because they are not high-efficiency condensing units. If you see water pooling around the base, it is either a leaking temperature and pressure relief valve, a cracked tank, or condensation on the cold water inlet pipe sweating in a humid environment. The T&P valve is the most common culprit. The manual instructs you to lift the test lever monthly to ensure it moves freely and does not weep afterward. If it weeps continuously, the valve is either failing or the static pressure in your home's water supply is exceeding the valve's rating. Most residential T&P valves are rated at 150 PSI and 210 degrees Fahrenheit. If your home's water pressure is above 80 PSI, which is common in older buildings with no pressure reducing valve, the T&P will weep periodically as a safety release. Installing a PRV upstream of the water heater will usually stop the nuisance dripping entirely. The venting requirements in the A.O. Smith Gas Water Heater Manual are strictly enforced by code and for good reason. Single-wall black pipe is acceptable for the first few feet from the unit in many jurisdictions, but most inspectors now require double-wall B-vent pipe for the entire run, especially if the vent passes through a wall or ceiling. The manual specifies minimum vent diameters based on the BTU input of your particular model. A 30,000 BTU heater might accept a four-inch vent, while a 75,000 BTU unit may require six inches. Using a smaller vent than specified will cause combustion gases to back up into the room, which is a carbon monoxide hazard. I once inspected a installation where the previous contractor had reduced the vent from six inches to four inches with a reducer collar because the hole in the exterior wall was the wrong size. The heater worked for about a week before the homeowner complained about a gas smell near the unit. The manifold pressure was too high because the exhaust could not escape freely. That reducer collar was the problem. Never reduce a vent unless the manufacturer explicitly allows it in the manual, and even then, verify with the local code official. Expansion tanks are another thing the manual mentions only in passing but that can cause real problems if you ignore them. Closed plumbing systems, which include homes with backflow preventers on the municipal supply or check valves on the well pump, have no place for heated water to expand into. The thermal expansion has nowhere to go, which increases pressure in the tank and the piping until the T&P valve lifts. The solution is a thermal expansion tank installed on the cold water inlet side of the water heater. A.O. Smith recommends sizing it based on your home's water volume and temperature rise, and the manual includes a chart for this. A typical 50-gallon residential unit in a city with 60 PSI incoming water and a 70-degree temperature rise usually needs a minimum of a two-gallon expansion tank. Going smaller will cause the T&P to weep every time the heater cycles on. I installed a three-gallon tank on a job where the previous installer had used a one-gallon unit, and the diaphragm in the small tank was ruptured within six months from constant over-compression. The larger tank resolved the issue completely.

If you are reading this because your heater is making noise, the manual has a section on rumbling and popping sounds. That is almost always sediment buildup at the bottom of the tank. The water gets trapped under a layer of mineral deposits, overheats, and flashes to steam, creating the noise. Draining the tank through the drain valve at the bottom will flush most of it out. Open the valve, let the water run until it is clear, and close it. Do this once a year and the noise will stop. If the sediment is severely packed, you may need to disconnect the cold water inlet and flush the tank in reverse, which is not covered in the manual but is a standard plumbing practice. I flushed a 120-gallon commercial A.O. Smith unit that had not been serviced in eight years and got about five gallons of thick sludge out of it. The heater ran quietly after that, but the efficiency was already degraded because the sediment was insulating the water from the burner flame. Electronic control boards on newer A.O. Smith models are reliable but not immune to failure. Moisture in the basement or garage is the number one killer of these boards. The terminals for the thermocouple, flame sensor, and gas valve can corrode over time, especially if there is any condensation or high humidity. If you are getting random ignition failures or error codes that do not match the manual's chart, check the terminal connections first. A little contact cleaner on the spade connectors and a tight reconnection often resolves issues that people mistakenly attribute to a bad board. I replaced a control board on a model that turned out to have a loose thermocouple wire that was intermittently touching the case and causing a short. The board was fine. Tightening the wire and wrapping the terminal with electrical tape fixed it permanently. The drain valve is another component that deserves attention. A.O. Smith typically uses a brass drain valve on their residential models, which is better than the plastic ones on some cheaper brands. Still, these valves fail if you never operate them. A quart of silicone spray or plumbing grease on the threads once a year will keep the valve from seizing. When you drain the tank for maintenance, open the T&P valve at the same time to break the vacuum and allow the water to flow out freely. If you do not crack the T&P, the tank may partially vacuum-lock and the draining process will take much longer than it should. The manual does not mention this trick, but it is standard practice among experienced technicians.

There is a limit to what any manual can solve. If the tank is leaking from the bottom, no amount of reading will fix it. The weld seams and the steel shell are the failure points, and once water appears at the base, the tank is compromised. A.O. Smith does not warranty tanks against internal corrosion, only against manufacturing defects, which is standard across the industry. If your heater is past its rated capacity and you are seeing leaks, replacement is the only option. The manual can guide you through the installation of the new unit, but it cannot reverse a corroded tank. Factor in the cost of a new unit, possible venting modifications, and a permit if your area requires one, and you are usually looking at a few thousand dollars depending on the model and complexity of the install.