Rheem and Ruud furnace code 45: low pressure switch open, inducer on high

Furnace control display or LED

“Low Pressure Switch Open, Inducer on High Speed”

(-)96P & (-)(-)96MDP, (-)96T & (-)(-)96MDT, (-)96V & (-)(-)96MDV, (-)97V, (-)98V, (-)802P UPFLOW/HORIZONTAL & (-)(-)80MDP, (-)802P DOWNFLOW & (-)(-)80DDP, (-)802V UPFLOW/HORIZONTAL & (-)(-)80MDV, (-)802V DOWNFLOW & (-)(-)80DDV · 92-24161-122-12 p. 88; 92-24161-157-04 p. 88; 92-24161-124-12 p. 117; 92-24161-126-04 p. 100; 92-24161-159-03 p. 97; 92-24161-146-05 p. 40; 92-24161-147-04 p. 35; 92-24161-148-07 p. 70; 92-24161-149-06 p. 65
Technician

What it means

45 is a code of the two-stage and communicating furnaces: the low pressure switch is open while the inducer runs at high speed. The communicating manuals add that this switch must close after the inducer starts and before the ignition sequence can begin 96V: 92-24161-124-12, p. 117. 45 is in the code lists of the 96P, 96T and 802P and on the fault cards of the 96V, 97V, 98V and 802V 92-24161-122-12, p. 88; 92-24161-146-05, p. 40; 92-24161-124-12, p. 117. Single-stage furnaces have no 45; their pressure switch code is 57 92-24161-111-17, p. 87; 92-24161-144-09, p. 39.

The communicating fault cards describe what follows. Gas heat stops; other modes such as cooling should still work. The code appears only after the inducer has run at least ten seconds. Before ignition, the inducer stays on high for five minutes from the start of the pre-purge, stops, and the control tries again until the switch closes or the call for heat ends. If the switch opens while the burners are lit, the gas valve closes, the blower runs at heat speed through a 90-second off-delay, the inducer finishes a 20-second post-purge on high, and the control tries to ignite again if the call for heat is still there 92-24161-124-12, p. 117; 92-24161-126-04, p. 100; 92-24161-148-07, p. 70.

The 96P and 96T cards describe the start-up case differently: if the low switch has not closed within 60 seconds, the control turns the inducer off and enters a 5-minute soft lockout, then starts proving the switch again, and repeats 92-24161-122-12, p. 94; 92-24161-157-04, p. 94. The lockout section of the 96V manual uses the same 60 seconds and five minutes and says this lockout resets itself after five minutes 92-24161-124-12, p. 121.

On the condensing communicating furnaces there is one more rule: if the low pressure switch fails five times in one call for heat, the control forces the high rate to reveal a possible water sensed condition, and the display shows a capital H whatever the thermostat asks for 92-24161-124-12, p. 93.

The card lists eight causes: blockage or improper termination in the inlet or exhaust vents; a vent longer, or with more elbows, than the maximum specified; a faulty or disconnected inducer; a faulty control board (inducer relay); loose or faulty wiring; pressure switch hoses that are disconnected, blocked, split or cut; sporadic wind gusts; a faulty pressure switch 92-24161-124-12, p. 117.

When 45 and 57 alternate

45 with 57 means both pressure switches are open when both should be closed. The communicating furnaces then show 45 and 57 in turn, with the top segment of the right digit lit for ½ second between them 96V: 92-24161-124-12, p. 93; 802V: 92-24161-148-07, p. 45; 92-24161-149-06, p. 40; 97V: 92-24161-126-04, p. 76; 98V: 92-24161-159-03, p. 73. The first editions of the 96P and 96T manuals name the same condition 46 and 57 92-24161-122-01, p. 88; 92-24161-157-00, p. 88, and their 2017 revisions list neither pair 92-24161-122-12, pp. 88–89. The high pressure switch side is on the 57 page.

Rheem’s owner’s manuals give no reset for 45 and 57 or for any other code (92-20802-128-03; 92-20802-130-02). The 96V installation instructions, written for qualified service personnel, say a lockout can be cleared immediately provided that the fault that caused it has been cleared and the power is turned off and on, or, for a soft lockout, the call for heat is off for more than 2 and less than 20 seconds 92-24161-124-12, pp. 1, 121. While a switch stays open, the card’s cycle of inducer runs and retries goes on 92-24161-124-12, p. 117. More on the board’s lockouts: clearing a code.

Check these first

The owner’s manuals have no step for 45. For a furnace that will not operate, the last of their operating instructions gives two 92-20802-128-03, p. 4; 92-20802-130-02, p. 4:

Turn off the gas to the furnace by “To Turn Off Gas To The Appliance”: shut off the manual gas valve in the gas supply piping outside the furnace casing, set the thermostat to its lowest setting, turn off all electric power to the appliance if service is to be performed, remove the burner access door, turn the gas control knob or switch to OFF and replace the door 92-20802-128-03, p. 4. In that list the power step is conditional, but the manual’s warning is to turn off electrical power to the furnace before removing the front access door 92-20802-128-03, p. 7, and its operating instructions turn off all electric power before the burner access door is removed 92-20802-128-03, p. 4. Full steps: shutting the furnace down.
Call your service technician or gas supplier 92-20802-128-03, p. 4.

The vent is the first cause on the card. The owner’s manuals mention it only as a warning: if the vent pipe has become disconnected, toxic fumes can escape into the home, so do not operate the furnace, and appropriate service must be applied 92-20802-128-03, p. 8; 92-20802-130-02, p. 8. The carbon monoxide warning on the cover of the installation instructions says to check that the furnace vent and air intake terminals are not obstructed in any way during all seasons 92-24161-124-12, p. 1; the owner’s manuals do not repeat it.

The condensing owner’s manual, which Rheem’s support site links from the 96P, 96T, 96V, 97V and 98V pages, adds that a pressure switch shuts off the main burners if the condensate drain line becomes blocked, and that the condensate flow can be checked by eye while the furnace runs 92-20802-128-03, p. 8. The site links the 80% owner’s manual from the 802P and 802V pages, and that manual has no condensate section (92-20802-130-02).

When to call a licensed technician

The card’s solutions are service work 92-24161-124-12, p. 117:

Checking the vent system for blockage and proper termination, and the vent length and elbows against the specification sheets and installation instructions; removing excess venting.
Repairing or replacing the inducer, its wiring and its electrical connections, or the control board.
Checking wiring and connections.
Replacing the pressure switch hoses or the pressure switch.
For wind gusts, proper termination and whether a high altitude kit may be needed.

The owner’s manuals leave routine maintenance to a qualified installer, service agency or the gas supplier 92-20802-128-03, p. 7.

Notes for different models

Series	Where	Wording	Source
96P, 96T, 802P	code list	“LOW PRESSURE SWITCH OPEN, INDUCER ON HIGH SPEED”	92-24161-122-12, p. 88; 92-24161-157-04, p. 88; 92-24161-146-05, p. 40; 92-24161-147-04, p. 35
96P, 96T	fault card, 60 seconds and a 5-minute soft lockout	same title	92-24161-122-12, p. 94; 92-24161-157-04, p. 94
96V, 97V, 802V	fault card, five minutes of inducer, then a retry	same title	92-24161-124-12, p. 117; 92-24161-126-04, p. 100; 92-24161-148-07, p. 70
98V	fault card, title only	same title	92-24161-159-03, p. 97
Fault code label 92-103343-01-00 (listed on the RGGE and RGJF support pages)	label, no models printed	“Low Pressure Switch Open - Inducer on High”	92-103343-01-00, p. 1
92P, 92T, 95P, 95T, 801S, 801P, 801T	code list	no 45; the pressure switch code is 57	92-24161-111-17, p. 87; 92-24161-144-09, p. 39

The 802P manuals give 45 only in the code list, with no fault card 92-24161-146-05, p. 40. The text of the 98V card could not be extracted, so this page does not paraphrase it. The neighbor code 46 is the same switch with the inducer on low speed; the 2017 96P and 96T lists print it “LOW PRESSURE SWITCH OPEN, INIDUCER ON LOW SPEED” 92-24161-122-12, p. 88. On the 96V and 97V diagnostics charts 45 is a warning or a critical fault (fault level 1,2), at priority 14 and 17 (96V-chart; 97V-chart).

For Ruud, the documents show only the replacement-parts line “www.myrheem.com/myruud.com” in the 802P manuals 92-24161-146-05, p. 50; 92-24161-147-04, p. 46 and the model name R801T on both a Ruud and a Rheem specification sheet (G22-556 Rev 8; G11-662 Rev 7); none ties a Ruud furnace to a series on this page.