Miller Furnace Shuts Down and blinks 3 times

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Posts: 1054
Joined: Sun Feb 18, 2007 3:24 pm

Been having some strange days with my furnace, a Miller MMHA-075AAHR-01, with not staying on. Years ago it went into lockout and the control box was blinking 3 times. I called a professional (?) that pressed the reset button on the upper limit switch and called it a ($) day.

6 years later my problem is back. At first I was thinking upper limit switch is faulty. But when it is fussy it does start properly and runs in full for 30sec to 5 min (varies), then shuts down too soon, blinking 3 times. After a few resets (off then on) it finally stays on long enough to warm up the house by the thermostat. Then it runs properly for a few days or a few weeks. Weather does not seem to be a factor, only the need for heat.

Since it is going completely through the startup/ignition and shutting off/error after being in full operation I am confused to the real cause. I am a vestal mechanic with electrical, electronic, and computer experience. I cannot find a good manual on this unit or anything close.

It is obvious something is telling it to shut down, but what component?

Dave
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Posts: 1054
Joined: Sun Feb 18, 2007 3:24 pm

Hi,

3 flashes is failed ignition, gas valve error or false flame sensed during warm up.

By what you describe, I would suspect first two.

Mostly the failed ignition, in which I would suspect the HSI Control #626421 or the Ignitor #902661A.

Both can be seen and ordered if needed at below link.

Check HSI Control for good ground.

Check Ignitor closely for hairline crack.

Check Ignitor positioning to be sure the burner flame is in contact with tip of Ignitor.

Disconnect Ignitor leads at receptacle and then test for 120vac at plug during Ignitor sequence.

Set meter to Ohms setting of RX1 and allow Ignitor to reach room temp., then with it disconnected, test for resistance. Should read 40-75 ohms.

Hope these help.

Take care and best wishes,
Robert

Link: http://www.mobilehomerepair.com/NordyneGas.html
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Posts: 1054
Joined: Sun Feb 18, 2007 3:24 pm

Thanks for the reply Robert!

Unit is still working since the last fussy day. So I will check it out more this weekend. To clear up one point, I have good ignition everytime. Full startup including main blower on with good airflow. When it is fussy I get the early shutdown. Once that period of time is over with, we are back to normal full operation.

Questions: (So I understand this unit better)
What actually senses proper flame? The gas valve? And if the sensor was dirty why would the problem be so intermittent?

What else can shut off the burner?

Any idea where I can download a real shop/service manual?

Meter in hand, will be looking at all connections this weekend.

Dave
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Posts: 1054
Joined: Sun Feb 18, 2007 3:24 pm

Hi Dave,

Even though it ignites and runs fine to start off, when it fails, it is still during Ignition phase.

The sensor will detect whether it is proper flame and if not after 6 seconds, the circuit to the GV is interrupted.

Anything electrical or electronic can/will/does on occasion fail intermittantly.

It can be dirty, burn off, reoxidize and be dirty again.

What I listed is main faults for 3 flashes at module.

No place to get manuals, most repairs on gas furnaces are not DIY. Without proper testing equipment, a wrong or false diagnosis can prove to be dangerous.

If those things I listed does not resolve it, have an experienced Tech inspcet it and advise.

I will be leaving shortly and not be back until Wednesday.

Will check back then.

Take care and best wishes,
Robert
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