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Thread: Digital Raypak RP2100, Low Nox Heater Not Heating Correctly

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    Digital Raypak RP2100, Low Nox Heater Not Heating Correctly

    I have a Digital Raypak 2100 that I am putting back in service after years of offline. Everything works as expected... pilot light, burner and controls. However, the water temperture in the SPA mode never gets above 80 degrees. I can see part of the burner flame and it appears to burn blue, with just a few flecks of sporatic yellow. The flame is not "blowing" above the burner, so gas pressure appears to be OK. The supply pipe is
    1 1/4", so the supply should be OK. I can't see if the flame is burning high enough ( I think it is supposed to be 4"). Any ideas that I can check. Thank you.

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    JasonLion's Avatar
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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    Welcome to TFP!

    If you have flame and nothing leaks there aren't very many ways for a heater to be broken.

    Check to see if the heater is also heating the pool water, and not just the spa. Various valve mis-adjustments can cause it to heat both, which will take way way longer and probably never get to full temperature.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    Thanks for the feedback. The heater is only connected to a SPA, so no other valve adjustments in the system. Is it possible that the flow of water through the heater is too fast... such that the burner cannot heat the water to spa temperatures?

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    JasonLion's Avatar
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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    No, water moving too quickly can damage the heater over time, but in the mean time it actually heats more efficiently.

    Are you sure that the thermostat isn't turning the flame on and off at the wrong temperature?
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    The flame is staying on all the time... and so is the "flame symbol" on the Control Panel. Question: Is there an inspection plate or site plate that I can access that will allow me to see the full flame on the burner. I can't locate any sight hole to get a full view of the burner flame... although I do know that it is burning all the time because I can see just a small portion of the flame.

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    JasonLion's Avatar
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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    The front panel comes off and you can see some things through there, which is what I assume you are doing already. Other than that you would have to do some fairly major disassembly. A small mirror on the end of a pole is handy in this kind of situation.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    Jasonlion, thank you for your assistance... and patience.

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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    Does your temp adjust by rotating a knob? If so, some of those models have a metal "ring" around the temp knob. There is a small screw head on that ring. The ring restricts the rotation of the knob, which in turn limits how high the water can be heated. If yours has that ring and screw, back out the screw a few turns and see if it allows you to rotate the limiter ring and knob, essentially asking for a higher water temperature.

    If you have hard water and, as you wrote, your heater has seen little use, there is a possibility that you could have scale build-up in the heater tubes. Depending on the amount of build-up, it could restrict flow through the heat exchanger, and possibly, restrict the amount of heat transferred. But I'm guessing there.

    Raypak's heater are field repairable though, and pretty much DIY-friendly. So you could open it up and take a look. Directions about using the reamer tool and cleaning out scale are in the manual.

    Good luck!
    20' x 40' plaster pool with 6'D 4-jet spa. Estimate 23K Gallons
    Raypak ASME 400k propane heater, Pentair Intelliflo pump, Pentair Quad DE 100 filter
    Liquid Cl via Stenner 45MPHP10 pump and Intermatic HB880R timer
    Loop-loc cover, Letro Legend II sidewall cleaner, soon to be replaced
    Live in CT, use pool from mid-APR to mid-NOV

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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    Mongo, thank you for your input. Mine is a Digital unit and has "Up-Down" touch screen controls for increasing/reducing temperature settings. So, no knob to rotate. I set the Mode to SPA (not POOL) and increase the setting to a higher temperature (eg... 100 degrees), but the water temperture never gets above 80 Degrees... either by the thermomter in the SPA, nor by the temp read-out on the control console of the heater. I am not able to confirm the strength of the flame on the heater as there is no easy access to see the burners. I can barely see a bit of the flame, which is blue, with a bit of yellow flecks, but I cannot see the height of the flame. I have thought about drilling a small sight hole near the burner area so that I can see inside the cabinet, but have not done so as I am not sure what is on the other side of the cabinet wall. If I could see that the flame is strong, then that pretty much narrows down the problem to the heat exchanger. One other point, the flow of water throught the heater is very strong. I have checked the flow at the circulation pump exhaust in the SPA and it is very strong. I had a Teledyne Lars unit before this Raypak, which I replaced due to rusted out water manifold, but it heated the SPA to 100 Degrees in about 1.0 hour. So, I know that the gas supply pipe at 1 1/4 inches is large enough to supply the proper gas pressure.

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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    Try setting it to POOL, crank it up to 100, and see if that gives you any different output. It will probably be the same as it's just another setting.

    Other than that, I'd remove the top and inspect the HX. Makes sure there's no debris between the fins.

    From the bottom, you should be able to catch a peek at the flame height but you have to get your head down low, ear-to-the-ground low. Maybe a small mirror to get a reflection? If your flame is too small, you could have insect debris or rust in the burner assembly or gas orificii. The burner tray is fairly easy to slide out to clean the burners. I had to pull mine last year to clean it. A small flame can also be due to low gas flow. If you're comfortable doing so you can source a manometer and check WC inches.

    Or just call a gas guy to come out.

    Good luck with it. Frustrating for sure. Without a doubt my happiest moment of opening up the pool is getting the heater to light off. Relief.
    20' x 40' plaster pool with 6'D 4-jet spa. Estimate 23K Gallons
    Raypak ASME 400k propane heater, Pentair Intelliflo pump, Pentair Quad DE 100 filter
    Liquid Cl via Stenner 45MPHP10 pump and Intermatic HB880R timer
    Loop-loc cover, Letro Legend II sidewall cleaner, soon to be replaced
    Live in CT, use pool from mid-APR to mid-NOV

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    Re: Digital Raypak RP2100, Low Nox Heater Not Heating Correc

    Thank you for the input.

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