Hayward H400FDN IF ignition failure voltage question


New member
Jul 22, 2017
Huntersville, NC
I was getting the IF code this spring right before we began using the pool for the summer. I turned off the heat pump this last week, because it was struggling to keep up now that it has gotten cold here. I went to troubleshoot the gas heater. I've been through all the steps I can find from Hayward but have had no luck. I'm thinking it could be the board. If I pull the igniter off the board I get a 120 volts when it first tries, but then will throw the IO code immediately and stop trying because it's unplugged. With the igniter plugged in the voltage fluctuates between 88 and 105 when it is trying to start, ie for about the 10 seconds when it powers the igniter. Under load would it be normal to see this voltage drop vs. unplugged? I've never seen this before in other types of applications. Any thoughts from someone that has more experience than I do?


Well-known member
Mar 30, 2019
Las Vegas, NV
What is happening before it shows the IF error code? The IF error code is for ignition failure. When the ignitor is powered it should glow an orange/red color. After a specified warmup time for the ignitor the gas valve should be powered ( you might be able to hear the gas valve solenoid click open). The burners should then be lit off and proven through the flame sensor. If the ignitor is not glowing when powered, you might have a bad ignitor or possibly ignition control. If the burners light off, but then drop out you probably have a dirty flame sensor. If you can let me know where in the sequence of operation something that is supposed to happen doesn't happen it would be easier to troubleshoot from there.


Gold Supporter
Jul 8, 2015
If you think there is an issue with the HSI, you can also check the resistance across the igniter leads. it should be between 40-90 Ohms. Higher than that and its likely bad. When they develop micro cracks they won't glow or don't heat up enough.