Dometic Toilet: “Red Full Tank light”
warning RV toilet warning lights
What it means
On the Dometic flush switch / MasterFlush status panel, the red Full Tank light is illuminated. When connected to a holding-tank monitor, this signals the tank is full. The control module then automatically cuts electrical power to the toilet so it cannot be flushed, preventing the holding tank from being overfilled.
Most likely causes
- Holding tank is full and the level system has shut down toilet power most likely
- Tank level sensor or its wiring faulty, giving a false full reading on an empty tank common
- Sensor probes fouled by waste or scale common
Safe checks you can do yourself
- Confirm the actual tank level before assuming a sensor fault.
- If the tank is empty but the red light persists, suspect a fouled or failing tank level sensor or its wiring.
- Dump and flush the tank, then recheck.
- Inspect the flush switch and control-module wiring for loose or corroded connections.
How to reset / clear Red Full Tank light
- Empty the holding tank.
- If the light does not clear, turn off the toilet's circuit breaker briefly, then restore power to reset the control module.
When to call a technician
The red light remains after the tank is confirmed empty, cleaned, and the sensor wiring checked, or the toilet stays powered down after a reset.
Applies to
Dometic 8700 series MasterFlush · Dometic MasterFlush macerator toilets with Dometic flush switch / DFT panel · Dometic 8100/8200/8300 series with Dometic flush switch and tank monitor
FAQ
What does Dometic Toilet code "Red Full Tank light" mean?
On the Dometic flush switch / MasterFlush status panel, the red Full Tank light is illuminated. When connected to a holding-tank monitor, this signals the tank is full. The control module then automatically cuts electrical power to the toilet so it cannot be flushed, preventing the holding tank from being overfilled.
How do I reset Dometic Toilet Red Full Tank light?
Empty the holding tank. If the light does not clear, turn off the toilet's circuit breaker briefly, then restore power to reset the control module.
What is the most common cause of Red Full Tank light on a Dometic Toilet?
The most likely cause is holding tank is full and the level system has shut down toilet power.
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Sources
- Dometic 8700 Series MasterFlush Toilet Operation Manual — Section 6.2.3 / 6.3.3 Indicator lights — red FULL TANK light; automatic full-tank shut-down; Troubleshooting item 3a (Dometic)
Note: The red light/auto shut-off only works when the toilet is wired to a holding-tank monitoring system; on installs without it the light may not function.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.