How can I get my SaniVite3 pump to work again?

We have a SaniVite3 pump that was used for a while, then held in storage for 3 years. We have just installed it again and the pressure pad will not detect the water, thus the pump doesn't activate. However, when we push the pad with our fingers, it does register and the pump does then activate. Is there anything that can be adjusted to increase the sensitivity, or is this not the answer?