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Thread: Hayward H300 Propane Milivolt not firing

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    Hayward H300 Propane Milivolt not firing

    Hello...I recently picked up a used Hayward H300 milivolt propane heater on CL...Before I became the proud owner, the heater had been bought and sold a couple times, with both of the previous owners never having actually hooked it no one really 'knew' anything about it. I now have it all hooked up and of course, it isn't working.

    I can get the pilot to ignite and stay lit, as long as I continue to hold down the pilot gas knob on the gas valve, and while holding down the knob, there is a strong blue flame...but once I let it go, the flame either goes out completely, or is very faint and when I attempt to turn the gas knob to the 'on' position, nothing happens.

    I traced the troubleshooting flowchart from Hayward and it seems to indicate a bad gas valve? Can anyone substantiate this? The HAXGSV0003 MV gas valve seems pretty expensive and I would prefer to have an accurate diagnosis, before purchasing it...

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    Join Date
    May 2007
    South Central NJ

    Re: Hayward H300 Propane Milivolt not firing

    Disconnect one lead off the pressure switch. There should be about 400 mV DC between the two after 45 seconds of the pilot flame hitting the pilot generator(aka thermocouple/heat sensor). If it's 0 mV, reconnect the wires and check for continuity through the safety circuit. I sincerely doubt its the regulator. They are pretty reliable devices. It could be the wires were chewed, bad hi-limits, or a bad pilot generator.

    Owner of - PoolGuyNJ LLC
    Expert Pool and Spa Repairs, Renovations, and Augmentation. Helping people decide what is the right gear for meeting their needs. Expectations Set, Expectations Met, No Surprises.

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