Bosch W275 water heater fault?

to use my lpg caravan water heater, I have to replace the batteries and turn on the taps / shower For the hot water. When I have finished using the heater, I have to remove the batteries again otherwise the piezo ignition sparks all the time and a small amount of gas lights and goes out every few seconds. It will do this constantly until I remove the batteries. There are no drips and no smell of gas. It did freeze up this winter and the copper feed pipe had 3 splits in it - now repaired. Any ideas?

B. Evans
March 2018