Sentinel HD35P E4 error and how to fix it without new parts (in many instances).

My Sentinel is is my encapsulated crawlspace. I live in TN and the summers are brutal. Hot and humid. This puts a load on the Sentinel.

After 11 months of perfect operation, I noticed the humidity creeping up in my crawlspace. I have two remote temp/humidity sensors down there that allow me to keep an eye on things from inside the house. You should also do this.

I went under the house and the unit was showing the E4 error code. This code means a problem with the condensate tray pumping system. There are three primary parts to the pumping system: The pump, the water uptake filter, and the float switch (and also the condensate pan).

Right when this occurred I tested the pump by pressing the “Drain” button on the control panel. The pump pumped water out. HOWEVER, it made some air bubble gurgles as it was pumping. I assumed the volume of water coming out was also normal. Air bubble gurgles are NOT normal. And the drain hose should be FULL of water when it pumps. If the water does not completely fill the inside diameter of the drain tube, you have a restriction and will get the E4 error. There should be no gurgling AT ALL. None. Not a single air bubble. There should be full bolus of water that fills nearly all of the drain tube in one drain (I have the full 19' of drain tube).

While under the house, I removed the service panel on the back and then removed the water pump uptake filter and float switch. I cleaned them both with paper towels and verified the float switch was floating. This was done crouched down in less than three feet of space in the crawlspace. I reinstalled the float switch and the pump uptake filter and reset the unit. It ran normally for a little while (an hour maybe?) and then it started short cycling (running for 4 minutes and turning itself off for 1.5 minutes, and repeating). And the humidity began to creep back up in the crawlspace. Strangely, it WAS pumping quite a bit of water out. I had the drain tube in a Tupperware container and in about 4 hours it filled it up. But no lowering of humidity and short-cycling. (If it pumps normally, it should put out a couple of cups of water in less than two hours, assuming your crawslpace is humid!)

I removed the unit from the crawlspace, which is a hassle. I made a little skateboard-like dolly with four casters that I could put the Sentinel on to roll out of the crawlspace. Game changer.

When out from under the house, I removed the service panel, removed the water pump, the pump uptake filter, and the float switch. I forced high pressure water through the pump (it is directional, so water will only blast out in one direction.), rinsed the float switch VERY well, and disassembled the pump uptake filter and blasted water inside and outside the filter. I also carefully cleaned the coils and fins with the garden hose and tipped the unit nearly on it’s side and blasted out the condensate pan. Some slime came out. Then I used an air compressor to blast the water out of the unit, paying close attention to the main control board which had a bit of light over spray on it. I vigorously blasted air through the coils and fins and in the condensate tray (with the unit tipped up). Then I blasted compressed air through the pump (remember: directional), the filter unit, and through the pump drain hose. There is a silicone sleeve over the top of the pump to protect it from moisture. I removed that, used steel wool to scrub off the light rust on the top of the motor, and replaced the silicone sleeve. I added a small dab of silicone caulk to the area where the wire exits the sleeve, thus making it water-tight.

I reassembled everything and ran the unit in my carport (outside humidity of 90%), for about an hour. HERE IS WHERE I SAW WHAT WAS WRONG: The water pump must have had slime and restrictions in it. It ran a drain cycle about every 10 minutes or so in the carport. And the volume of water coming out of the pump was at least SEVERAL TIMES the volume when I pushed the drain button previously. This thing is pumping A LOT of water and does not have gurgles. After running for an hour outside, it had about 4 drain cycles and put out A LOT more water than it was putting out before.

So what was going on? The float switch WAS working properly. And it was cycling the pump. But the pump was only pumping maybe 20% of the volume it should have been pumping. The pump runs for about 14 seconds (or less, depending on the float switch position). The pump was not able to drain the condensate tray in the time allotted, leading to a constantly full condensate tray and thus the E4 code.

It did not need parts. It needed disassembly, flushing, compressed air, and reassembly. (I also cleaned the air filter with compressed air). You have to clean ALL FOUR PARTS: The pump, the pump uptake filter, the float switch, and the condensate tray. Clean the coils and fins while you are doing this.

Runs like new. Good luck.