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Thread: Hayward H400FDN Ignition Failure

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    Re: Hayward H400FDN Ignition Failure

    I am also having the IF issue. I took everything apart today to a take a look and everything looks fine with no spider webs. I did not take of the the jets to look at them when I had the burner tube off so I will need to do that tomorrow. Mine starts up with all the clicking and I can see the flame through the window for about 2 to 3 seconds and then it goes out so I know I am getting some kind of flame. My heater is less than 1 year old. How can I check the flame sensor? It has been raining very heavily here and the insulation inside where the burner tubes go is soaking wet, could this be causing the problem? There are no leaks what so ever when it's not raining so i don't think that I have a leak. I am going to order a cover to prevent the inside from getting soaked in case that that's what is causing the problem. Any help is appreciated.

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    Re: Hayward H400FDN Ignition Failure

    The insulation should not get wet just because it's raining. It's a sealed unit and nothing can get inside like rain. Usually when this is like this it is because there is a leak in the heat exchanger. It could be a very small leak spraying all over inside.
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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    Re: Hayward H400FDN Ignition Failure

    The flame sensor works by a process known as flame rectification. An AC signal is sent along a wire to the flame sensor. A good blue flame will act as an electrical rectifier. A rectifier converts the AC signal to a DC signal. The control module senses the DC current and confirms flame.

    If flame is not good or not present at all, there will not be a good DC current.

    Most likely, the water in the insulation is fouling the flame and the flame is not good enough to support the DC microamp signal. This causes the control module to shut off the gas.

    As noted above, wet insulation is probably due to a leaking heat exchanger. The Hayward heater uses a two-tube four-pass exchanger instead of a four-tube two-pass exchanger.

    In my opinion, having only two tubes creates excessive velocity in the copper tubes and results in excessive erosion of the exchanger. I would estimate the water velocity to be above 20 feet per second.

    The leaks seem to be primarily near where the water enters the first tubes going into the exchanger. I suspect it's where turbulence is created as water transitions from the header to the tubing.

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    Re: Hayward H400FDN Ignition Failure

    I have seen in these Hayward units where a portion of the heat exchanger is weaker than the rest of the exchanger. When I take them apart, it looked like during the manufacturing process there is a glitch which causes the week spot. I don't see turbulance as being the issue but more of a weak spot in the copper to begin with. Hayward never had this issue with the older ED series units.
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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    Re: Hayward H400FDN Ignition Failure

    I think that the older units had 4 tubes and a double pass. The newer units use 2 tubes and four passes. This doubles the speed of the water going through the tubes, which greatly increases the erosion.

    In any case, the Hayward heat exchanger seem to develop pinhole leaks more than average.

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    Re: Hayward H400FDN Ignition Failure

    Here is one guy that fixed his. Not your regular DIY job for most folks. Hayward H350FDN Heat Exchanger Repair - YouTube
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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    Re: Hayward H400FDN Ignition Failure

    Thanks for all of the responses. I did check the gas orifices and they were clean. My heater is less than one year old and I am now suspecting a small leak like noted in the posts above. I did replace the flame sensor so I know that wasn't the problem. I will take the unit apart this weekend if I have time and see if I can find a leak. The leak is most likely small since I do not see any water anywhere and all I felt was the wet insulation. Does anyone know if I can remove all of the panels and run the heater so I can see if there's a leak, that's what my plan is for this weekend. Is there anyway that It could still be the flame control board? The heater lights up for about 3 to 4 seconds and then shuts off.

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    Re: Hayward H400FDN Ignition Failure

    Quote Originally Posted by JamesW View Post
    The flame sensor works by a process known as flame rectification. An AC signal is sent along a wire to the flame sensor. A good blue flame will act as an electrical rectifier. A rectifier converts the AC signal to a DC signal. The control module senses the DC current and confirms flame.

    If flame is not good or not present at all, there will not be a good DC current.

    Most likely, the water in the insulation is fouling the flame and the flame is not good enough to support the DC microamp signal. This causes the control module to shut off the gas.

    As noted above, wet insulation is probably due to a leaking heat exchanger. The Hayward heater uses a two-tube four-pass exchanger instead of a four-tube two-pass exchanger.

    In my opinion, having only two tubes creates excessive velocity in the copper tubes and results in excessive erosion of the exchanger. I would estimate the water velocity to be above 20 feet per second.

    The leaks seem to be primarily near where the water enters the first tubes going into the exchanger. I suspect it's where turbulence is created as water transitions from the header to the tubing.
    Is there a logical way that I can test this theory out? I have access to meters and a scope? How is the circuit formed, does it originate at the flame sensor board and terminate to a ground through the flame? Is there a way to bypass or fake it so I can rule this out? I also think that running the heater for an hour might also dry the insulation out which might help if it did in deed get wet during a very wet week here.

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    Re: Hayward H400FDN Ignition Failure

    You can put a meter in series with the flame sensor to see if you're getting the correct dc current. I think it should be about 3 to 5 microamps. You can try cleaning the sensor. Wet insulation might be interfering with the dc microamp signal.

    Don't do anything that you're not sure that you can do safely. Don't operate a gas heater unless you're sure that it is in good working order. Typically, when the exchanger goes and soaks everything, you might be better off replacing the heater.

    Flame Sensor Testing Furnace - YouTube

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    Re: Hayward H400FDN Ignition Failure

    Quote Originally Posted by JamesW View Post
    You can put a meter in series with the flame sensor to see if you're getting the correct dc current. I think it should be about 3 to 5 microamps. You can try cleaning the sensor. Wet insulation might be interfering with the dc microamp signal.

    Don't do anything that you're not sure that you can do safely. Don't operate a gas heater unless you're sure that it is in good working order. Typically, when the exchanger goes and soaks everything, you might be better off replacing the heater.

    Flame Sensor Testing Furnace - YouTube
    Thanks for the words of caution and that great link. I am an electrical engineer by trade so i understand most of the risks of messing with electricity and flammable gasses. I hope to be able to find the root cause this weekend by measuring the current for the flame sensor circuit like exhibited in the video.

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    Re: Hayward H400FDN Ignition Failure

    I had an opportunity to take a quick look at the heater last weekend. I was able to use the resistor/diode combination to get the heater running which tells me that the problem is definitely being caused by a rectification failure. I let the heater run for an hour in order to heat up the hot tub to 100 degrees hoping that would dry out the inside of the heater. It seemed to work later when I tried to start the heater without the resistor\diode and it started up like it should. I then tried again the next day after running the pumps all night without the heater on and the IF code was back and the heater failed to start. I am guessing that there's a leak even though I can see it and it's is causing an issue with the rectification of the AC voltage that is being output at the end of the flame sensor. I will open the heater up when I have more time and see if I can locate the source of water if there is one or if there is some other issue with the rectification circuit. Everything is properly grounded so I am suspecting a leak in my 6 month old heater. Not a happy camper and will never purchase a Hayward product again.

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    Re: Hayward H400FDN Ignition Failure

    Since this unit is so new, why haven't you called Hayward about this? Did you not have this installed by a licensed installer?
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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    Re: Hayward H400FDN Ignition Failure

    Sometimes it's just a dirty or bad flame sensor. Cleaning the flame sensor can sometimes solve the problem.

    However, in this case, a leak is the most likely cause.

    Did you check for the dc microamp current?

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