E-13 indicates no fuel to the heater. Look on the bottom right side of the heater. You'll see two small screws and a large screw. Shut off fuel flow to the heater. Make a U shaped channel with a piece of heavy duty aluminum foil and place it under what you see there. remove the LARGE screw. This bleeds off any fuel in the sump. Now remove the two smaller screws and the plate and gasket. Pull out the spring which is connected to the stainless steel filter basket. Clean the filter with GUMOUT. Use a Q tip with GUMOUT on it and clean out the recess where the filter element went. Re-assemble the chamber, turn on the fuel and start the heater. Press the RED button. This will release the internal float.