A.O. Smith with HSI not lighting the burner.

Old 02-08-10, 01:57 PM
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Unhappy A.O. Smith with HSI not lighting the burner.

I have a 50G A.O. Smith power vented water heater with a hot surface ignition. Problem is it's not lighting the burner. I've already replaced the HSI but it doesn't seem to be venting gas. HSI glows oranged then everything kicks off before the gas ever starts. About 20 seconds later the process restarts. I find it odd that the control panel isn't reading an error. It will try to light all day if I don't power it off. Any ideas?
Old 02-08-10, 09:10 PM
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It sounds like it may be in your safety circuit. I am not familiar with this exact unit, however, most power vented units have the same type of safety circuits.

Look for a 'vacuum switch' which should have a tiny little hose on it. Make sure the switch is operating (closing) when the inducer kicks on. You may check this by taking off the two leads and using a test meter on the resistance reading. It should close when the inducer kicks on and open when it stops. The meter should read a short when the inducer is on and nothing when it is off.

If that checks good look for any 'roll-out' sensors or 'spill' sensors. These are usually button type sensors that 'open' when high temps. are detected and some must be re-set manually, some re-set automatically, and others are one-time use and must be replaced. If you have any, and I am not sure if you do, look for a little red button in the center between the two wires and push it in and check with a meter like the other one before. Make sure that you pull off the wires before testing.

Like I said, you may not have any, or there may be one or two that may have been field added and did not come with the unit, etc... but IF you have any---check them all. There may be one on the smoke pipe (duct) that you will need to check too. Most people miss this one! If ANY ONE is open, the main burner will not come on and the unit may attempt to fire the burner all day, depending on the unit. Most units today 'lockout' after a pre-determined amount of failed attempts but water heaters use a variety of systems and may also be wired for additional safety in the field.

Good luck.


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