Thetford Toilet: “Red tank LED (full)”
warning RV toilet warning lights
What it means
The single tank-symbol LED on the wall switch glows solid red. This means the system is powered on and the high-level (full) sensor on the holding tank has been triggered. The controller then locks out the water inlet so the bowl will not refill, which prevents you from adding more waste and overflowing the tank. The macerator pump itself stays available.
Most likely causes
- Holding (black) tank is genuinely full and needs to be dumped most likely
- Tank level sensor probes coated with waste, tissue, or mineral scale giving a false full reading on an empty tank common
- Loose, corroded, or damaged wire between the high-level tank sensor and the toilet control module less common
- Failed sensor or control module rare
Safe checks you can do yourself
- Confirm the actual tank level on your RV monitor panel or sight gauge before assuming the sensor is wrong.
- If the tank is empty but the light is red, the high-level sensor is usually fouled — flush the tank thoroughly with water and a tank cleaner and let it sit.
- Inspect the sensor wiring and connectors at the tank for looseness or corrosion.
- Verify supply voltage is roughly 12V (or 24V on 24V units) with no large voltage drop while the macerator runs.
How to reset / clear Red tank LED (full)
- Empty/dump the holding tank if it is actually full.
- Turn the toilet off at its circuit breaker, wait about 60 seconds for the controller to fully power down, then restore power.
- If the light clears to green/yellow after the tank is emptied, normal operation is restored.
When to call a technician
The red light stays on after the tank is confirmed empty, cleaned, and the sensor wiring checks out, or if the macerator will not run after a reset.
Applies to
Tecma Silence Plus 2G · Tecma Elegance 2G · Tecma Silence Plus · Tecma macerating RV toilets with single tank-symbol wall switch
FAQ
What does Thetford Toilet code "Red tank LED (full)" mean?
The single tank-symbol LED on the wall switch glows solid red. This means the system is powered on and the high-level (full) sensor on the holding tank has been triggered. The controller then locks out the water inlet so the bowl will not refill, which prevents you from adding more waste and overflowing the tank. The macerator pump itself stays available.
How do I reset Thetford Toilet Red tank LED (full)?
Empty/dump the holding tank if it is actually full. Turn the toilet off at its circuit breaker, wait about 60 seconds for the controller to fully power down, then restore power. If the light clears to green/yellow after the tank is emptied, normal operation is restored.
What is the most common cause of Red tank LED (full) on a Thetford Toilet?
The most likely cause is holding (black) tank is genuinely full and needs to be dumped.
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Sources
- Tecma 2G Silence Plus Toilet RV Owner's & Installation Manual — 98269 Rev. E, Operation — Wall Switch LED states and Full Tank Lockout (A.4-5, A.4-6) (Thetford Corporation)
Note: Tecma uses one multi-color tank-symbol LED rather than numbered codes. A persistent false red on an empty tank from a dirty/stuck high sensor is widely reported by owners but the manual only documents the red = full-and-lockout behavior.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.