We've been having an issue with our gas Water Heater for quite a while. It is about 4 years old. When it starts up the blower will come on for about 10 seconds then the burner will light and stay lit for only about 2-3 seconds then goes out and the blow shuts off. It will then do this again and usually stays running on its second attempt, however sometimes it doesn't start after 3 attempts then goes into lockout mode and we have to power it off then back on so it can try again. It seems that it never fires up correctly on the first try but usually does on the second. Any suggestions as to what I should check look at? Thanks for any help!

Check for gas leaks around the valve. If there aren't any, check the thermocouple (that would be the copper rod leading into the bottom of the water heater). It could need replacing.

Your unit may be a system that uses a flame sensor and these will get corroded over a period and will need to be cleaned or replaced.

I agree that really sounds like how a furnace with a dirty flame sensor behaves. You may find some helpful details at https://www.askmehelpdesk.com/heatin...ons-58313.html

The attached image is from the manual. Do you think the "sensor" mentioned in the diagram is the flame sensor?

Yes I would say that this is the flame sensor and it should be cleaned or replaced. If you can find one in your area you should just replace it while you have it out. If not rub the sensor prong with some very fine grit sand cloth.

I pulled it out and cleaned it off (with a scouring pad) and that seems to have fixed it! At least for now... Thanks for the help.