Rheem Furnace Shuts off after 5-7 minutes

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Old 01-28-19, 07:28 AM
K
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Exclamation Rheem Furnace Shuts off after 5-7 minutes

New user, looking forward to helping a single grandmother in my community get back to a warm home!

Unit: Rheem RGPH-07EAUER horizontal installation
Symptoms: Furnace fully ignites and runs blower with warm air being sent to house, but shuts off gas after 5-7 minutes. Confirmed multiple times control board does NOT indicate any failure codes (no blinks at all, just flame sensor LED de-energizes). After gas shutoff both inducer and blower motors run proper shutdown sequence, then process starts over again.

Checks:
Removed thermostat and wire-nutted RH and W wires to ensure thermostat is not issue.
Cleaned flame sensor, no change. Unit detects flame properly (LED energizes) upon flame-on.
Cleaned supply/return registers, fully opened, slightly longer runtime.
Ran unit fully open with finger on blower door switch, no change.
Confirmed flue outlet is clear of obstructions

Diagnosis is unknown, but it seems like a limit switch issue with overheating either the coil or the discharge air, or just a bad limit switch.

Ready with a multimeter to start diagnosis, but want to confirm what I am looking for.
Grounding, looking for continuity between inducer fan ground connection and furnace body.
Furnace limit switch - do I watch ohms for anything except 0?
Flame rollout limit switch - do I watch ohms for anything except 0?
Inducer pressure switch operation - check for continuity once inducer fan is running, any OL is failure?

There does NOT seem to be a limit switch on the flue stack, but perhaps I am missing where it might be

It does not seem like there is any dirt/dust/grime in the burner housings and minimal dust on the squirrel cage blower, everything looks to be clear.

Thanks for any help you might be able to provide!

Kevin
 
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Old 01-28-19, 01:27 PM
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Is this a direct spark ignition or a hot surface ignition system ?
In the link below should be your furnace. It shows that the control board will issue a fault on the OK LED.

Rheem RGPH-07 manual (pdf)
 
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Old 01-28-19, 04:18 PM
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What makes you think there is anything wrong. Is this a new problem or existing.

Furnace just might be oversized, reaching high limit before stat is satisfied then blower continues to run until its sensor shuts it down.

With the stat jumped out does the burner eventually come back on by itself with the blower still running as though the stat was still calling for heat.
 
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Old 01-28-19, 07:34 PM
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hot surface ignition

The problem is even with the white and red tied together at the thermostat (heat forever) it still shuts off after 5-7 mins. With the thermostat in place it shuts off before reaching temp. I'm to the "System runs until call for heat ends" with a no response there I checked ground to be good (disconnected and reconnected wire, confirmed continuity). I cleaned the flame sensor last night. I think it just needs a control board. Will report back! We recently had a big power outage from downed lines around here and electronics of all sorts are doing weird things...
 
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Old 02-19-19, 12:34 PM
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FYI for those who find this in 2037, it was the control panel. Replaced it and all is working great.
 
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