Snubbers are a capacitor and resistor combination device that helps reduce EMI (electromagnetic interference) when a large inductive load is turned off.  

A standalone snubber can be found on some devices wired directly across a coil, like on a contactor.  For ease of wiring some output boards have snubbers onboard that are prewired in the circuit. 
Milnor also produces snubber boards which mount many snubbers on one board allowing easy connection.  These boards only have one connection to the low side of  the control power.  If this connection is faulty the snubbers will allow a feedback to other connected devices and may confuse troubleshooting techniques.  So, check the low side connection if some components do not turn off when commanded.  
Snubbers can be used in 120 volt and 240 volt control circuits.  The low side connector on 120V circuits is normally ground. But, 240 volt machines use a low side connection at the "bottom side" of the 240 volt circuit.   

On the I/O board for some 240 volt controls on small washers, you need to know that connector M3, pin 12 is the low side connection point.  

M3-12 should be tied to TB6. If it is not there, add it. If it is loose, fix the connection. This is the bottom side of 240V AC for a number of snubbers. The absence of this wire could cause a valve to stay as long as any other output is on. This can cause an overfill due to a water valve not turning off when commanded due to a feedback of voltage across the valve.