Yes I have had a similar problem with mine( SHURflo SR600 ).It is just over 12 mths old,bought it direct from Williamson Pumps,spoke to them,could be a problem with some of the pure water accidently soaking the switch when pouring it in.
You can order a new switch approx £45,just waiting to fit mine,I will let you know how I get on, speak to them they are very helpfull.0845 226 3638
Steve