A common symptom of a submersible pump malfunctioning is when water stops being pushed, but the motor still hums. That hum almost always indicates that the pump's motor is still good but the impeller needs to be replaced.  

Installation is easy:

1) Use a Phillips screwdriver to take pump cover off intake (use a manual screwdriver to avoid stripping the screws). 
2) Pull old impeller out (may need pliers with more powerful Pondmaster models).
3) Make sure inner chamber is clean with no debris and smooth to the touch (with no pits or rough areas).
4) Check that O-Ring is still positioned along the housing. Apply a thin film of silicone grease along the surface of the O-Ring.
5) Then, simply insert new impeller into place and reattach pump cover.

Pro-tip : Also check inside of the pump cover because it may also be worn or damaged. Replaceable pump covers (aka:volutes) are available and other pond pump replacement parts can be bought from here.

For optimum preventative maintenance, it is recommended to replace both the impeller and the pump cover (volute).

While all of these impellers are very similar in design, it is very important you select the correct model!

Each impeller is compatible with both Pondmaster and Supreme Danner models:

# 12655 : for model 1.5 (140 GPH)

# 12955 : for model 1.9 (190 GPH)

# 12555 : for model 2 (250 GPH)

# 12575 : for model 3 (350 GPH)

# 12575 : for model 5 (500 GPH)

# 12585 : for model 7 (700 GPH)

# 12746 : for model 9.5B (950 GPH)

# 12756 : for model 12B (1200 GPH)

# 12776 : for model 18B (1800 GPH)

# 12791 : for model 24 (2400 GPH)