This may be the result of one of the IDF or SDF valves being stuck in a closed or partially closed position. Using the Diagnostics screen select "Valve Test" and look for "IDF Inlet", "SDF Inlet" and "Waste" buttons. Run a brief test using the screen to open and close each valve. Confirm by looking at the pinch valve at the back of the instrument to see that it is opening and closing properly.
If any of the valves are not opening properly, refer to TDF Service Procedure TS008 to replace the pinch valve. The TDF29 Pinch Valve Assembly-IDF/SDF or TDF29.1 Pinch Valve Assembly- Waste can be ordered through the Product Catalog on this website or by calling 315-986-8090.