My response from François PICOT at Lagoon was enlightening - although more about Lagoon service
than a technical fix. After asking me a question to clarify the issue he then came out with the very wise solution "yes one is automatic the other is manual". What???
My solution to date has been to flush a lot of fresh water through the sensor and bilge pump and it does seem to start and stop (including the alarm) OK. I have labeled the circuit breakers for the port and starboard emergency Rule
2002 bilge pumps. Not the best solution to turn it off, but acceptable short term if confirmed that there is no leak. I have also checked that the Whale Gulper pumps works well as does the manual pump.