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Flame Sensor Test

Have you tried this? What's the model? What did you find?



  • Techman
    Techman Member Posts: 2,144
    Flame Sensor Test

    HI All!How do Gas Roof Top Units and Swimming Pool Heaters that use Flame Sensors test the sensor itself ,this is with spark ignition and/or glow coil.Some literature[Fenwal] refer to "test ports" on the spark module,I've never seen them!

    In this case a Teledyne/Lars pool heater;glow coil glows ,gas ignites for 1 sec.and then shuts down,the flame sensor was replaced and the gas stayed on for 2-3 sec. and shuts down.I will be looking at the unit tomorrow ,so,THANKS IN ADVANCE!
  • carol_3
    carol_3 Member Posts: 397

    Often the problem is that the ignition module isn't grounded to the burner. This ground is important because it makes sure that a complete circuit exists for the "message" to get to the module that there's flame and it's safe to release gas for the burner to light. The presence of flame completes that circuit. Flame conducts electricity. But without a burner ground, the message doesn't always get through, or for long.
  • Techman
    Techman Member Posts: 2,144

    Hi Carol!Should I be testing the microamps ?How? and how much?Thanks again!
  • Empire_2
    Empire_2 Member Posts: 2,343

    Those test points are little silver in color dots. I don't know which module you have, but you could always call the tech rep and he can guide you thru it. UA,....depending on the module it can range from 1.0 to 5 or 6. Cleaning is also a big thing. check gas pressure to make sure the unit is firing properly, and pull burners and clean. I am assuming this in a direct fire unit or "Spark to Explosion" as I call it.??

    Mike T.
  • Rich W
    Rich W Member Posts: 175

    Ditto to everything above. It's been a few years since I've seen a Fenwal. Does it have the flat edge connector? If the sensor is hard-wired to the connector, you can cut the wire and test there. I believe you can also check that module by installing your uA meter in series with the burner ground wire. Seems to me the Fenwals want a higher uA reading than Honeywell does. Double check power to the gas valve- had two jobs one summer where the valve was trying to draw over 3amps from a 40va transformer. The symptoms LOOKED like a dirty sensor or bad module. It only takes a few minutes to take the readings. I don't know where you are as far as skill and experience but here's a little tip. Get a little all-in-one clamp meter. Set it to capture the max amp reading (5 to 20A setting). Then clamp it around the output of the transformer and cycle through the tests with your other meter. If something tries to draw more than 1.66amps from a 40va transformer, you've got a problem waiting to happen. Then it's just a matter of locating the guilty load. I guarantee you'll be the guy that catches the intermittent problems that other people miss. Happy hunting.

  • Known as " Rectification "

    Called "Flame Rectification"

    Hope that helps
    He who knows WHY

    Shall be master of

    He who knows HOW
  • Techman I e-mailed you some

    information on this subject did you get it?
  • Darin(in Michigan)
    Darin(in Michigan) Member Posts: 90

    I've been in flooded basements where the humidity was extremely high and for some reason the unit wasn't registering a good flme signal. Once the basment dried out the unit ran fine. It might also be noteworthy the location of the chemicals to the pool heater. I would imagine caustic materials can degrade wire. Just my 2c.
  • Empire_2
    Empire_2 Member Posts: 2,343

    I know what you are getting at, but I think what you will find in certain scenarios there is either a poor ground OR loose connection. DC flame rectification is like water,....It will seek the easiest path, and take it. No doubt that hi RH% can effect this circuit, but if the ground is clean and tight there should be no problem. Good observation though. Just as a notation,...Any equipment that has been subject to flooding requires replacement of all devices pertaining to Nat. Fuel Gas Code.

    My O2

    Mike T.
  • Rich W
    Rich W Member Posts: 175

    I would agree Darin. I've seen basements with standing water (not up to the equipment)with this problem.

    Try unplugging the sensor from the module and checking the resistance (connect ohmmeter to burner ground and the sensor wire). Even extremely high ohms will short-out a signal of .0000008 amps by providing a path to ground. Your standard meter may show and open circuit but a "megger" would show a path to ground via condensation on the ceramic.
    I think this is why a cracked ceramic causes problems- moisture can't evaporate very well without heat.

    Good luck
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