Before you replace it... open up the top and take out the guts of the head. Check carefully for sand and dirt. Also check the bottom of the body for the same. I've found 3500's are very finnicky to getting gummed up by sand. If you find any, rinse thoroughly and put it back together and try it out. My experience has been about 50% will start to work again after this process. If this doesn't work, it is time to replace.
