[BlueBSH]

Water heater was working fine, until recently. Water would get cold fast... well the other day the water went cold and didn't recover, looked at it, and it was just sitting there, not error codes blinking on the heater controler or anything... turned it off and back on (this is a power vent water heater).. blower fan came on, watched the hot surface ignitor come on, heard the gas valve open after a couple seconds heard gas, then the ignitor went off and no flame... then it retried that a couple times...

cleaned the flame sensor, not that it would help but did it anyways and retried it. no luck.

got old fashioned, and decided to light it manually when the gas came on... lit fine, and kept running... strange thing is after this manual light it works fine again... any time the hot surface ignitor comes on now, boom flame when the gas comes on...

any ideas what would cause this to happen?

 

[AllanJ]

Did you have to unscrew a sealed hatch to reach in and light it manually?

Did you leave the hatch ajar after that time?

Your heater may have an air intake cutoff that prevents flammable vapors from the outside (such as spilled cleaning fluid) from getting in and flaring up and causing a fire hazard. If your heater has this and it trips you need to follow specialized instructions to get it reset. If you left the hatch ajar more than just a crack, the heater may operate without having the intake cutoff reset.

Maybe the orifices in the burner nearest the igniter are clogged with rust or dirt. Then before enough gas from the other holes gets close enough tothe igniter, the normal safety mechanism shuts off the gas flow before the burner can start. If you get a "boom" when it does start then you probably have this problem.