How to diagnose and repair a faulty atmospherically-vented, gas-fired water heater. Common problems and how to fix them. Example tank is a John Wood 40 gallon: Model AV40N Same tank as A.O. Smith 40 gallon: Model GCRL 40 Status Light Codes Normal Flashes: • 0 Flashes Indicates Control Off/Pilot Out. • 1 Flash Indicates Normal Operation. • A continuous light indicates that the gas control valve/thermostat is shutting down. Diagnostic Flashes: If the water heater is not working, look for the following diagnostic flashes after lighting the pilot. 2 Flashes Indicates Thermopile Voltage Low 4 Flashes Indicates Overheat Failure 5 Flashes Indicates Sensor Failure 7 Flashes Indicates Electronic Control Failure 8 Flashes See “Status Light and Diagnostic Code Troubleshooting Chart.” Troubleshooting Chart: https://www.manualslib.com/manual/743692/A-O-Smith-Gas-Water-Heater.html?page=33 Related Videos: Control Valve Replacement https://youtu.be/5f6UFwRlXr8 Thermopile Replacement https://youtu.be/1VIvEqVbt14 Thermopile Voltage Test https://youtu.be/mtbn3FtMqCM 𝗔𝗺𝗮𝘇𝗼𝗻 𝗔𝗳𝗳𝗶𝗹𝗶𝗮𝘁𝗲 𝗟𝗶𝗻𝗸𝘀 Thermopile 100112328: https://geni.us/tglX2B Thermopile Assembly 100112330: https://geni.us/p4gHRaE Control Valve 9007884005: https://geni.us/ZJJkIB Control Valve WT8840B1000: https://geni.us/2Kj3p 𝗦𝘂𝗽𝗽𝗼𝗿𝘁 Want to support my channel or give back? Help me improve on these DIY videos by making a financial contribution. All contributions no matter how small are greatly appreciated! https://ko-fi.com/prosdiy Thank you! 𝗖𝗼𝗻𝗻𝗲𝗰𝘁 More DIY videos! https://www.prosdiy.com Facebook: https://www.facebook.com/prosdiy Instagram: https://www.instagram.com/prosdiy Subscribe: https://www.youtube.com/c/prosdiy Amazon: https://www.amazon.com/shop/prosdiy Disclosure: Pros DIY is an Amazon Associate. We earn a small commission from qualifying purchases through our affiliate links at no additional cost to you. Videos produced by Pros DIY (https://www.prosdiy.com) are provided for informational purposes only. Please check with all national, state, provincial, and local codes and regulations before attempting any work. Pros DIY does not assume any responsibility or liability for any damage or injury from the information provided in our videos. Please hire a licensed, certified, professional.