Water Heaters - Rheem Water Heater wont stay lit

My Rheem gas water heater wont stay lit sometimes. The igniter glows, the burner lites, but will occasionally turn off after about 5 seconds. The HS780 controller will try 2 more times, and if it doesnt stay lit, it goes into lockout mode. The ignitor measures under 30 ohms when hot, and about 175 ohms when cold. These numbers seem to be ok per Rheem. I get 24 volts at the gas valve when the valve is open. Might be my imagination, but seems to go into lockout mode overnight when the water heater doesnt run. I think the controller might be bad but looking for some advice.

The module needs proof that the flame has been established. This is done either thru a flame sensor built into the ignitor [local sense] or a separate flame rod somewhere around the burner[s][remote sense]. What actually happens is the flame is used to conduct a very small current to ground which proves the flame. The flame is conducting electricity which how the module knows the flame has been established. Over time the flame sensing rod gets a coating on it which interferes with the flame sense circuit. Cleaning or replacing the flame rod is the solution. If it's part of the ignitor, smply replace the ignitor. If it's s remote sense flame rod, try cleaning it but also check the ceramic closely for a crack. My experience has been that the modules are either go or no go, rarely intermittent.

Daddyjohn, thanks for the info. It's a combo ignitor flames sensor. It checks under 30 ohms when hot which is in spec. I have also tightened the ground screw on the module. Do u still think it's the ignitor? Thanks again.

It would be the flame sensor, not the ignitor per se. How is the area where the ignitor bracket attaches? Clean, bright, tight? There are only a few econds in which the module waits for the flame sensor circuit to be established. One test is to check the flame sensor current to the module. It's in microamps so you would need a digital VOM that will read that low. You hookup the meter is series with the sensor wire that goes back to the module. Of course you have to know the spec number as well. Like I said before, my experience has been that modules either work or they are kaput.

Thanks for the info. I will try a new ignitor I guess.

ok let us know how you make out. thanks.

Well, yesterday, it wouldnt light at all. So I went home and checked the voltage supplied to the gas valve while it was trying to light and it was 13-14 volts, not 24 volts as was spec'd. In order to have hot water, I powered the gas valve from the 24 volt line to the Ignition Control and it stayed lit for the 20 minutes or so that I ran it. I repeated this 2 more times last night and this morning. I replaced the Ignition Control and it started right up. However, irst time it started up, the burner cut off again after about 20 seconds (approx) and then lit successfully on the 2nd try. It continued to run OK, then I had to leave for work. I am hoping that it was a startup issue and not the old issue still there. On a side note, I have never been happy with the placement of the ignitor I used last fall because it had a different mounting bracket. It was the OEM replacement, but it placed the ignitor such that the burner flam hits the ignitor at its midpoint, not near the tip as the documentation suggests. It has worked for 6 months that way, but I thought it might be worth mentioning. Any ideas if this positioning might be part of the problem?

It still fails to light and locks out. So tomorrow I have a new water heater being installed. 50 gallon power vent. I guess I should feel lucky I got 17 years out of the old one.

thanks for the update I hope the new one is less trouble