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Rinnai 431FA direct vent propane furnace

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Johnski
Johnski Member Posts: 3
in Gas Heating
Hello, I've got a 22ish year old Rinnai furnace, 431FA III in a small house that's been trouble free.

https://media.rinnai.us/salsify_asset/s-19768263-5b55-47ce-a13d-40e5d225f51e/RHFE-431FAIII Installation and Operation Manual.pdf

But...it would not light a few weeks ago, it had spark, but seemed like there was no gas.

I believe one of the 2 gas shutoff solenoids is bad (one is redundant). One reads 1.6kOhm the other 1.7MOhm (bad). I have temporarily bypassed the bad solenoid by pulling the piston out of it. That whole solenoid gas control block is on order. I assume those 2 solenoids are either on or off.

The third solenoid on that block has an adjustment screw on it and a diaphragm type deal, but since it's been working for 20+ year, I figure I'd not touch it. But maybe something is off with that part of the gas control block. Now that I'm writing this I suppose it's possible that that diaphragm part could be leaking or something.

I've had some luck getting it to light and run, but it usually stops working again. And doesn't look like it's burning correctly.

I'm measuring the gas pressure differential using a homemade water manometer and the pressure seems like it's way too high and the adjustments in the manual are not making any difference. My manometer is measuring about 10" WC (which is basically the house supply pressure) but the spec for the difference should be .8"WC on low and 2.8"WC on high.

"Adjusting the pressure" involves some push button switches on the PCB and what I assumed were the < and > temperature buttons on the outside panel. So I turn the furnace on, press button 5 then button 4 for forced low and then pushing the < and/or > to try to adjust, but the manometer reading doesn't change. The same happens when trying to adjust while on forced high.

I just had a thought, though, maybe when the manual says the < and > buttons, it's referring to the other 2 buttons on the PCB (there are 5 buttons in close proximity).

There are 4 DIP switches that should be all on, ON ON ON ON for propane and OFF OFF ON ON for ng. When I first took it apart I took some pictures for reference. I could have sworn the switches were ON OFF ON ON, but my pictures have a wire blocking the view on that switch so I don't know. I've set them all to ON as the manual says for propane.

My other gas appliances seem to work correctly. I haven't had any luck in finding somebody to work on it, so I'm trying to learn/fix it myself.

I'm fairly handy, but I'm not sure what to test next, especially since the gas pressure differential seems way off and the adjustment procedure doesn't make a difference.

Any thoughts?

Thanks,
John

Comments

  • Johnski
    Johnski Member Posts: 3
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    A new (used) solenoid control block seems to have fixed the problem. The pressure can now be adjusted as expected. Odd that 2 solenoids seem to have gone bad at the same time.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,834
    edited February 2023
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    Yea, I think taking apart a gas valve is not the best idea. You know... being an explosive gas and all. I wonder when we will see you in the news?

    DIY GAS HEATER REPAIR
    CAUSES EXPLOSION IN RESIDENTIAL NEIGHBORHOOD


    Film at eleven!
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Johnski
    Johnski Member Posts: 3
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    Nah, I did not take the new solenoid block apart. But to fair, I am a mechanical engineer, HVAC is just not my area. And I couldn't find anybody to work on it, so I had to do what I had to do.

    -note house is in the boonies, so the shrapnel shouldn't do too much damage. ;)

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