Struggling with E4 error on your Sentinel HD35P? User James shared a detailed DIY fix that works—no new parts required!
👉 The Problem:
● After 11 months of use, crawlspace humidity spiked, and the unit showed E4 error (condensate system issue).
● Testing the "drain" button: Pump worked but gurgled, with little water in the tube (should fill the entire tube with no bubbles).
👉 Repair Steps (Easy to Follow):
1. Initial Cleaning:
Crouched in the crawlspace (under 3ft tall), removed the back service panel, took out the pump uptake filter and float switch. Cleaned with paper towels, checked if the float floated normally. Restarted—worked briefly, but short-cycled (4 mins on, 1.5 mins off) after 1 hour, humidity rose again.
2. Deep Disassembly (Critical!):
Moved the unit outside (used a wheeled dolly for easy transport) and fully disassembled:
○ Removed the pump, uptake filter, and float switch; rinsed with high-pressure water (pump is directional—water only flows one way);
○ Took apart the uptake filter, rinsed inside and out;
○ Hosed down the condensate pan (slime came out), blew dry coils, fins, and control board with an air compressor (to avoid water damage);
○ Scrubbed light rust on the pump motor (with steel wool), added silicone caulk to the wire exit for waterproofing.
3. Verification:
Ran outside (90% humidity) for 1 hour—drained every 10 mins, with several times more water than before, no gurgles, and no short-cycling.
👉 Key Takeaways:
● E4 isn’t always a broken part! 90% chance it’s clogs from slime/debris—clean 4 parts: pump, uptake filter, float switch, condensate pan (plus coils/fins).
● The drain tube must fill with water (no bubbles) when pumping. James’ pump only pushed 20% of normal volume, causing a full pan and E4.

Runs like new now! Try this if you have the same issue—thanks James for the tips!