Rheem furnace 3 blinks: limit circuit open (RGPN, RGPS, RGLN, RGLS, green LED)

Furnace control display or LED

3 blinks

“Limit circuit open”

RGPN / RGPS UPFLOW/HORIZONTAL, RGLN / RGLS DOWNFLOW; (-)GPN / (-)GPP, (-)GLN · INSTALLATION INSTRUCTIONS FOR UPFLOW/HORIZONTAL & DOWNFLOW INDUCED DRAFT GAS FURNACES RGPN/RGPS UPFLOW/HORIZONTAL SERIES RGLN/RGLS DOWNFLOW SERIES, p. 39
Technician

What it means

In the installation instructions for the Rheem RGPN, RGPS, RGLN and RGLS series, the troubleshooting chart has a legend headed “BLINK CODES (GREEN LED)”, and 3 blinks there is “Limit circuit open” 92-24161-38-12, p. 39. The 2005 edition of these instructions, for the (-)GPN, (-)GPP and (-)GLN series, prints the same legend 92-24161-38-05, p. 37.

Separately, an undated Rheem support article, “Standard Furnace Diagnostic Flash Codes”, lists “3 Blinks = Limit Switch Open”. It names no models and no LED color, and says: “Does not include Modulating, LXE, or Two Stage furnaces.” (TP0002)

Rheem’s FAQ, which also names no models, gives two places to look for 3 blinks: the main high limit control, which may be open because of low air flow or an over-fired heat exchanger, and the manual reset rollout switch above the burner, which may have tripped (Rheem support article “Gas Furnace Technical Frequently Asked Questions”, undated).

The Safety Features section of the RGPN, RGPS, RGLN and RGLS instructions, separate from the code legend, explains both parts 92-24161-38-12, p. 35. The high limit’s cut-off temperature is set at the factory and cannot be adjusted; it keeps the air leaving the furnace from exceeding the maximum outlet air temperature and shuts the furnace down if it does. The reasons a limit switch opens “almost always involve low airflow”: a dirty or restricted air filter, a dirty or restricted cooling coil, an undersized or restricted return or supply air system, a problem with the main blower (wrong speed tap, failing motor bearings, low voltage to the motor, dirty blower wheel, wrong rotation, wheel slipping on the shaft), overfiring with too much gas pressure, and ventilation problems. The flame roll-out switches shut the furnace down in a flame roll-out condition in the burner compartment. A tripped roll-out switch must be manually reset, but the same paragraph says: “DO NOT jumper or reset this switch.” A qualified installer, service agency or the gas supplier should be called to diagnose and correct the cause of tripping.

The same instructions describe a limit test for service technicians, done with the limit wires removed to simulate an open limit 92-24161-38-12, p. 31. With the wires removed during the pre-purge of a call for heat, the indoor blower should turn on, three blinks should flash, and the unit will not light until the limit circuit is closed. With the wires removed during steady heat, the flame should go out immediately, three blinks flash, and the indoor blower and inducer should keep running until the limit is closed. With no call for heat, cooling or fan, the newer controls ignore an open limit circuit; the instructions give the reason as open limits in hot attics, which Rheem’s reliability department identified as a potential field issue 92-24161-38-12, p. 31.

Check these first

No owner’s manual for the RGPN, RGPS, RGLN or RGLS series is among the Rheem documents used for these pages, and the installation instructions give an owner no checks for 3 blinks. What the instructions give an owner:

1. They refer you to the lighting instructions on the furnace itself 92-24161-38-12, p. 30.
2. Their start-up steps end with: if the appliance will not operate, shut the furnace down and call your service technician or gas supplier 92-24161-38-12, p. 30.
3. For a tripped roll-out switch they say: “DO NOT jumper or reset this switch” 92-24161-38-12, p. 35.

A dirty or restricted air filter is the first reason on the limit list 92-24161-38-12, p. 35. The same instructions ask the installer to advise the customer to keep the air filters clean and to arrange furniture and drapes so the supply air registers and return air grilles are unobstructed 92-24161-38-12, p. 38. Their maintenance warning is to disconnect main electrical power to the unit before attempting any maintenance 92-24161-38-12, p. 36. They do not present filter care as a fix for 3 blinks.

If the furnace overheats or the gas supply fails to shut off, the instructions say to shut off the manual gas valve to the appliance before shutting off the electrical supply 92-24161-38-12, p. 30.

When to call a licensed technician

• A tripped roll-out switch. The instructions send it to a qualified installer, service agency or the gas supplier to diagnose and correct the cause 92-24161-38-12, p. 35.
• The checks in Rheem’s FAQ: excessive manifold pressure, and a blocked flue or heat exchanger (Rheem support article “Gas Furnace Technical Frequently Asked Questions”, undated).
• The other limit reasons: the cooling coil, the size and restriction of the return and supply air systems, the main blower and its motor, the gas pressure and ventilation 92-24161-38-12, p. 35.
• Testing the limit and its circuit. The instructions’ limit test uses an ohmmeter and removed limit wires 92-24161-38-12, p. 31.
• The vent and heat exchanger. Holes in either can let toxic fumes into the home, and a leaking vent pipe or heat exchanger must be replaced; the instructions recommend that a qualified installer, service agency or the gas supplier inspect the flue passageways, vent system and main burners 92-24161-38-12, p. 38.

Notes for different models

Board or series	Code	Wording	Source
RGPN, RGPS, RGLN, RGLS (blink legend, green LED)	3 Blinks	“Limit circuit open”	92-24161-38-12, p. 39
(-)GPN, (-)GPP, (-)GLN, 2005 edition (blink legend, green LED)	3 Blinks	“Limit circuit open”	92-24161-38-05, p. 37
Rheem support article TP0002 (models and LED color not named)	3 Blinks	“Limit Switch Open”	TP0002
7-segment code lists: 92P, 92T, 95P, 95T, 96P, 96T, 802P	22	“MAIN LIMIT OPEN”	92-24161-118-16, p. 87; 92-24161-154-03, p. 87; 92-24161-111-17, p. 87; 92-24161-120-16, p. 87; 92-24161-122-12, p. 88; 92-24161-157-04, p. 88; 92-24161-146-05, p. 40; 92-24161-147-04, p. 35
7-segment code lists: 801S, 801P, 801T	22	“MAIN LIMIT OR HALC OPEN”	92-24161-142-15, p. 39; 92-24161-143-14, p. 34; 92-24161-144-09, p. 39; 92-24161-145-10, p. 34
7-segment code lists: 92P, 92T, 95P, 95T, 96P, 96T, 801S, 801P, 801T, 802P	33	“MRLC (MANUAL RESET LIMIT CONTROL) (AKA ROLL-OUT) OPEN”	92-24161-118-16, p. 87; 92-24161-154-03, p. 87; 92-24161-111-17, p. 87; 92-24161-120-16, p. 87; 92-24161-122-12, p. 88; 92-24161-157-04, p. 88; 92-24161-142-15, p. 39; 92-24161-143-14, p. 34; 92-24161-144-09, p. 39; 92-24161-145-10, p. 34; 92-24161-146-05, p. 40; 92-24161-147-04, p. 35
Communicating 96V, 97V, 98V, 802V (fault cards)	23	“HALC OPEN”	92-24161-124-12, p. 115; 92-24161-126-04, p. 98; 92-24161-159-03, p. 95; 92-24161-148-07, p. 68; 92-24161-149-06, p. 63

The documents do not match blink counts to the two-digit codes; the rows for 22, 33 and 23 are other boards, listed here for comparison.

The board behavior depends on the board version. For single-stage equipment, the RGPN, RGPS, RGLN and RGLS instructions describe a control change effective in the third quarter of 2004. The earlier controls (part numbers 62-24140-02, 62-24268-01 and 62-24268-02) turn on the indoor blower and inducer when the limit circuit opens during steady “on”, continuous fan or a cooling call; the newer ones (62-24140-04, 62-25338-01, 62-24268-03 and 62-24192-01) do not 92-24161-38-12, p. 30.

TP0002 leaves out modulating, LXE and two-stage furnaces. The furnaces with a 7-segment display report limit faults as the numbers in the table above, not as blinks 92-24161-144-09, p. 39.

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