Roborock S8 Pro Ultra (S81USP) the mop is not washed

Cause 1 of 4The mop is not used, so it is not washed. Source: Common Issues, p. 15

First checkRun a mopping clean so the mop is used.

Causes and checks

The mop is not used, so it is not washed. Source: Common Issues, p. 15
1. Run a mopping clean so the mop is used.
The robot did not start from the dock, or no dock is found on the app map. Source: Common Issues, p. 15
1. Start the robot from the dock.
The clean or dirty water tank is not placed correctly, is empty or is full. Source: Common Issues, p. 15
1. Check tank placement and refill or empty as required.
The water filter is not correctly installed. Source: Common Issues, p. 15
1. Check that the water filter has been correctly installed.

Other S8 Pro Ultra (S81USP) problems

The robot will not power on2 causes in the manual. First: the battery level is low.
The robot will not charge2 causes in the manual. First: the dock may not be receiving power.
The robot charges slowly2 causes in the manual. First: the robot automatically reduces its charging speed at high or low temperatures to extend battery life.
The robot cannot dock2 causes in the manual. First: there are too many obstacles near the charging dock.
The robot behaves abnormallyThe robot behaves abnormally without showing an error.
The robot is noisy during cleaning2 causes in the manual. First: the main brushes, side brush, main wheels or omnidirectional wheel may be jammed.
The robot cannot connect to WiFi5 causes in the manual. First: wiFi is disabled.
Poor cleaning ability or dust falling out3 causes in the manual. First: the dustbin is full.
Scheduled cleaning is not workingThe battery level is low; scheduled cleaning can only begin when the battery level is above 20%.
No or little water during moppingThe water tank may be empty, or the scrub intensity or the mop installation needs checking.
Cleaning does not resume after recharging2 causes in the manual. First: the robot is in DND mode, which prevents cleanup.
The robot cannot return to the dock after spot cleaning or being movedAfter spot cleaning or a significant position change the robot regenerates the map; if the dock is too far away it may not return to recharge.
The robot misses certain spotsThe wall sensor or cliff sensors may be dirty.
Reduced emptying performance or unusual noise when emptying2 causes in the manual. First: the main brushes or main brush cover are not properly installed.
Reduced mop washing performance2 causes in the manual. First: the mop is not attached properly.
Auto-emptying is not working4 causes in the manual. First: auto-emptying is disabled.
Poor drying effect3 causes in the manual. First: auto Drying is disabled in the app.

Sources

Roborock S8 Pro Ultra FCC EN User Manual (EN/FR/ES). Beijing Roborock Technology Co., Ltd. Document S81USP, revision Undated download (PDF created 2023-03-14), 15 pages, en. support.roborock.com. Listed on the manufacturer's support page. Retrieved 13 November 2026.
What should I do when error 4 occurs?. Beijing Roborock Technology Co., Ltd. Document Article 360035369132, revision Undated web article, 1 pages, en. support.roborock.com. Listed on the manufacturer's support page. Retrieved 13 November 2026.
What should I do when error 5 occurs?. Beijing Roborock Technology Co., Ltd. Document Article 360035369172, revision Undated web article, 1 pages, en. support.roborock.com. Listed on the manufacturer's support page. Retrieved 13 November 2026.
What should I do when error 7 occurs?. Beijing Roborock Technology Co., Ltd. Document Article 360035369212, revision Undated web article, 1 pages, en. support.roborock.com. Listed on the manufacturer's support page. Retrieved 13 November 2026.
What should I do when error 9 occurs?. Beijing Roborock Technology Co., Ltd. Document Article 360035731551, revision Undated web article, 1 pages, en. support.roborock.com. Listed on the manufacturer's support page. Retrieved 13 November 2026.
What should I do when error 10 occurs?. Beijing Roborock Technology Co., Ltd. Document Article 360035731571, revision Undated web article, 1 pages, en. support.roborock.com. Listed on the manufacturer's support page. Retrieved 13 November 2026.
What should I do when error 13 occurs?. Beijing Roborock Technology Co., Ltd. Document Article 360035369312, revision Undated web article, 1 pages, en. support.roborock.com. Listed on the manufacturer's support page. Retrieved 13 November 2026.
What should I do when error 18 occurs?. Beijing Roborock Technology Co., Ltd. Document Article 360035731631, revision Undated web article, 1 pages, en. support.roborock.com. Listed on the manufacturer's support page. Retrieved 13 November 2026.

Page numbers are the numbers printed in the manual. Where this page and the manual differ, follow the manual.

Applies to: S8 Pro Ultra (variants S81USP; EWFD07LRR; EWFD08LRR). United States (FCC edition).
Source: Roborock S8 Pro Ultra FCC EN User Manual (EN/FR/ES), S81USP revision Undated download (PDF created 2023-03-14); What should I do when error 4 occurs?, Article 360035369132 revision Undated web article; What should I do when error 5 occurs?, Article 360035369172 revision Undated web article; What should I do when error 7 occurs?, Article 360035369212 revision Undated web article; What should I do when error 9 occurs?, Article 360035731551 revision Undated web article; What should I do when error 10 occurs?, Article 360035731571 revision Undated web article; What should I do when error 13 occurs?, Article 360035369312 revision Undated web article; What should I do when error 18 occurs?, Article 360035731631 revision Undated web article
Last verified: 13 November 2026
Handbook: Roborock S8 Pro Ultra robot vacuum in Robot vacuums; all Roborock handbooks