Hayward H400 ignition problem

[nickco201]

Hey,
I have a Hayward H400 natural gas, electronic ignition from approx 2005-2006 model. It worked great for the first two years, then we had to replace the heat exchanger, once again worked great for a few years with no leaks. Last year it would light then shut off but generally it would eventually stay lit after a few tries, however by middle of the year say July, it wouldn't stay lit at all. I cleaned etc etc etc, eventually replaced the flame sensor ( even though the old was not damaged or rusted), this seemed to fix it, it generally worked fine the rest of the year. This year with the new flame sensor from last year, it simply won't stay lit. I have cleaned the jets that are right by the access panel but not the actual burner under the heat exchanger. Once again the thing will light and burn, then 5-8 seconds later it will turn off, you can hear the ignitor sparking almost the whole time it is lit even though it lights immediately. I inspected the flame sensor, it is 100% new looking with no defects or rust. Any suggestion? I really would rather not pay 300$ for a tech to come out and look at it. I do a lot of plumbing/ electrical work on diesel locomotives for a railroad so feel pretty comfortable about fixing it, I just don't know where to start.
Thanks!

 

[Qwaxalot]

Try polishing the flame sensor a bit. A dollar bill works good for this

 

[danpik]

All classic signs of a flame sensor problem. First, as has been suggested clean the flame sensor wire/probe. Check the insulator for cracks, dirt, etc. Also check all terminals to make sure there is no corrosion. Next, make sure the sensor is well enveloped in the flame when it is on. Make sure all burner tubes, especialy the ones near the flame sensor, are clean and burning good. Check all wiring to the heater. (Is this a plug-in unit or hard wired?).A flame sensor needs a good ground connection to function properly. F.inaly, there was some reports of certain heaters that had to have some vent openings closed off as the air flow thru them caused the flame to lift off the burners and move away from the sensor. Not sure of the models though

 

[ps0303]

If the ignitor looks good and lets say you even clean it a bit and still have the issue, it could be the system board of which the flame sensor plugs into. The flame sensor/ignitor could be sensing flame but it's not registering with the board. Especially if you still hear it trying the light even after it's been lit.