Our Whale water pump which is connected to a Truma Combi water heater is intermittently running. It stays on for 10 seconds then off for 1 second and repeats this. The green run light on control panel mirrors this. I can't see any leeks and not losing water. All taps and shower run great and water is nice and hot. We are currently on a site and having to switch pump off at panel to stop over running of pump. I've drained and refilled system several times thinking it may bean air lock as this is first trip since last September. I thought it may be the Truma ultraflow smart switch so have fitted a new one today however the problem still exists. This is on a Bailey Pursuit 430/4 2017 model. Any suggestions welcome.