How House Works

Rheem and Ruud furnace code 66: blower cutback (high static pressure)

By How House Works EditorialBased on Rheem installation instructions, diagnostics charts and support pagesChecked against sources Updated

Furnace control display or LED

66

“Blower Cutback”

(-)96V & (-)(-)96MDV, (-)97V, (-)98V, (-)802V UPFLOW/HORIZONTAL & (-)(-)80MDV, (-)802V DOWNFLOW & (-)(-)80DDV · 92-24161-124-12 p. 120; 92-24161-126-04 p. 103; 92-24161-159-03 p. 100; 92-24161-148-07 p. 73; 92-24161-149-06 p. 68
Technician

What it means

66 is an airflow warning on the communicating furnaces with an ECM blower: the 96V, 97V, 98V and 802V. The blower motor is running at the highest speed or torque its specifications allow, but at the present static pressure the system needs more to reach the desired airflow. The motor’s own software keeps it inside the permitted range, so it keeps running, and it reports the condition to the furnace control 92-24161-124-12, p. 120; 92-24161-148-07, p. 73.

Rheem’s card says the code is meant to tell the installer about inadequate airflow due to excessive static pressure in the duct system, that it is “not intended to be a fault code”, and that it is “merely an operating indicator” 92-24161-124-12, p. 120. The card rates it non-critical: all operation, thermostat calls included, continues as normal, and blower operation may be slightly compromised 92-24161-124-12, p. 120. The 96V diagnostics chart gives 66 fault level 1, a warning, at priority 20 (96V-chart).

The card also limits when you see it. 66 is not displayed after the first three minutes of blower operation following a power reset, and it is not logged in the fault history after the first hour of operation; the fault buffer logs it once at most 92-24161-124-12, p. 120. While the burners are lit, the control alternates the mode letter h or H with a fault such as 66 that lets gas heat continue 92-24161-124-12, p. 93.

The card’s cause is a blower that has hit the maximum speed or torque limit because the static pressure is too high. Its solution names ductwork that is improperly designed or restricted for some other reason, or a filter that needs cleaning or replacing, and says to remove the obstruction or repair the duct so the static pressure does not exceed the published values in the specification sheets or installation instructions for the furnace 92-24161-124-12, p. 120.

Check these first

The furnace keeps running with 66, and the owner’s manuals have no step for the code (92-20802-128-03; 92-20802-130-02). The card names a filter that needs cleaning or replacing 92-24161-124-12, p. 120; filters are an owner’s task in the manuals, which also ask for clear registers and grilles. In the manuals’ order:

  1. The manuals ask you to arrange furniture and drapes so the supply registers and return grilles are unobstructed 92-20802-128-03, p. 4; 92-20802-130-02, p. 4. The 66 card does not name registers or grilles.
  2. Keep the air filters clean: inspect them monthly and replace them if necessary, and have your installer, service agency or gas supplier show you how to reach them. Put the filter rack door back properly afterward 92-20802-128-03, p. 7; 92-20802-130-02, p. 7. The warnings on that page say to disconnect main electrical power to the unit before any maintenance and to turn off electrical power to the furnace before removing the front access door.

The card addresses 66 to the installer, and measuring static pressure or changing ductwork is not in the owner’s manuals 92-24161-124-12, p. 120. The manuals leave routine maintenance to a qualified installer, service agency or the gas supplier 92-20802-128-03, p. 7.

When to call a licensed technician

  • Measuring the static pressure and comparing it with the published values for the furnace 92-24161-124-12, p. 120.
  • Finding and removing a duct obstruction, or repairing ductwork that is improperly designed or restricted 92-24161-124-12, p. 120.
  • A blower fault code on top of 66. Code 60, “BLOWER FAULT - BLOWER CAN STILL RUN”, has the same static pressure cause and adds a blower running at the temperature limit; 61 means the blower cannot run at all 92-24161-124-12, p. 119.

Notes for different models

Series Where Wording Source
96V, 97V, 802V fault card “BLOWER CUTBACK” 92-24161-124-12, p. 120; 92-24161-126-04, p. 103; 92-24161-148-07, p. 73; 92-24161-149-06, p. 68
98V fault card, title only “BLOWER CUTBACK” 92-24161-159-03, p. 100
96V, 97V, 98V diagnostics charts “Blower Cutback”, fault level 1 96V-chart; 97V-chart
Fault code label 92-103343-01-00 (listed on the RGGE and RGJF support pages) label, no models printed “Blower Overspeed Fault” 92-103343-01-00, p. 1
92P, 92T, 95P, 95T, 96P, 96T, 801S, 801P, 801T, 802P code list no 66 92-24161-111-17, p. 87; 92-24161-122-12, p. 88; 92-24161-144-09, p. 39; 92-24161-146-05, p. 40

On the 97V chart 66 is at priority 25 (97V-chart). The fault code label 92-103343-01-00, which prints no models and is listed on Rheem’s RGGE and RGJF support pages, calls 66 “Blower Overspeed Fault” and gives no description, so this page does not say whether it means the same thing as Blower Cutback 92-103343-01-00, p. 1. The 98V card text could not be extracted, so this page does not paraphrase it.

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.

Related Rheem and Ruud codes

  • 60 “Blower Fault - Blower Can Still Run”
  • 61 “BLOWER FAULT – BLOWER UNABLE TO RUN”
  • 68 “No Blower Communications”

See also

Other gas furnaces: Carrier, Goodman, Lennox

All Rheem and Ruud codes

Rheem and Ruud is a trademark of its owner. How House Works is not affiliated with or endorsed by Rheem and Ruud.

Sources

  1. Rheem Manufacturing. USER'S INFORMATION MANUAL UPFLOW/DOWNFLOW/HORIZONTAL CONDENSING GAS FURNACES. 92-20802-128-03 SUPERSEDES 92-20802-128-02; listed July 2017. Accessed Oct 20, 2026.
  2. Rheem Manufacturing. USER'S INFORMATION MANUAL UPFLOW/DOWNFLOW/HORIZONTAL 80% GAS FURNACES. 92-20802-130-02 SUPERSEDES 92-20802-130-01. Accessed Oct 20, 2026.
  3. Rheem Manufacturing. Specification sheet, Endeavor Line Classic Series gas furnaces, R801T UH. G11-662 Rev 7. Accessed Oct 20, 2026.
  4. Rheem Manufacturing. Specification sheet, R801T upflow/horizontal series, 80% AFUE. G22-556 Rev 8. Accessed Oct 20, 2026.
  5. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR 4 POSITION CONDENSING SINGLE STAGE SINGLE-STAGE GAS FURNACES (-)95P SERIES, (-)(-)95MSP SERIES. 92-24161-111-17 SUPERSEDES 92-24161-111-16; listed November 2017. Accessed Oct 20, 2026.
  6. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR 4 POSITION CONDENSING TWO-STAGE, PSC GAS FURNACES (-)96P SERIES & (-)(-)96MDP SERIES. 92-24161-122-12 SUPERSEDES 92-24161-122-11; listed December 2017. Accessed Oct 20, 2026.
  7. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR UPFLOW/HORIZONTAL SINGLE STAGE GAS FURNACES WITH CONSTANT-TORQUE AIR CIRCULATION BLOWER (-)801T UPFLOW/ HORIZONTAL SERIES (-)(-)80MSX UPFLOW /HORIZONTAL SERIES. 92-24161-144-09 SUPERSEDES 92-24161-144-08; listed December 2017. Accessed Oct 20, 2026.
  8. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR UPFLOW/HORIZONTAL TWO STAGE PSC GAS FURNACES (-)802P UPFLOW/HORIZONTAL SERIES (-)(-)80MDP UPFLOW/HORIZONTAL SERIES. 92-24161-146-05 SUPERSEDES 92-24161-146-04; listed December 2014. Accessed Oct 20, 2026.
  9. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR DOWNFLOW TWO STAGE PSC GAS FURNACES (-)802P DOWNFLOW SERIES (-)(-)80DDP DOWNFLOW SERIES. 92-24161-147-04 SUPERSEDES 92-24161-147-03; listed December 2014. Accessed Oct 20, 2026.
  10. Rheem Manufacturing. Serial Communicating Gas Furnace Fault Code Label (sheet “FAULT CODES”). 92-103343-01-00. Accessed Oct 20, 2026.
  11. Rheem Manufacturing. Diagnostics chart “DISPLAY CODES” (97V_ Trouble-Shooting_Chart.pdf, linked from the R97V and R98V pages). 97V-chart. Accessed Oct 20, 2026.
  12. Rheem Manufacturing. Diagnostics chart, untitled (96V_Trouble-Shooting_Chart.pdf, linked from the R96V page). 96V-chart. Accessed Oct 20, 2026.
  13. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR 4 POSITION CONDENSING TWO-STAGE, COMMUNICATING GAS FURNACES W/ECM BLOWER (-)96V SERIES & (-)(-)96MDV SERIES. 92-24161-124-12 SUPERSEDES 92-24161-124-11; listed December 2017. Accessed Oct 20, 2026.
  14. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR UPFLOW CONDENSING MODULATING, COMMUNICATING GAS FURNACES W/ECM BLOWER (-)97V SERIES. 92-24161-126-04 SUPERSEDES 92-24161-126-03; listed January 2017. Accessed Oct 20, 2026.
  15. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR UPFLOW CONDENSING MODULATING, COMMUNICATING GAS FURNACES W/ECM BLOWER (-)98V SERIES. 92-24161-159-03; listed March 2018. Accessed Oct 20, 2026.
  16. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR UPFLOW/HORIZONTAL TWO STAGE, COMMUNICATING GAS FURNACES W/ECM BLOWER (-)802V UPFLOW/ HORIZONTAL SERIES (-)(-)80MDV UPFLOW/ HORIZONTAL SERIES. 92-24161-148-07 SUPERSEDES 92-24161-148-06; listed December 2017. Accessed Oct 20, 2026.
  17. Rheem Manufacturing. INSTALLATION INSTRUCTIONS FOR DOWNFLOW TWO STAGE COMMUNICATING GAS FURNACES WITH ECM BLOWER (-)802V DOWNFLOW SERIES (-)(-)80DDV DOWNFLOW SERIES. 92-24161-149-06 SUPERSEDES 92-24161-149-05; listed March 2017. Accessed Oct 20, 2026.