Plugging in the 15 amp lead causes one of the two circuit breakers inside the van to trip; the air-con circuit is OK. Have checked behind all powerpoints for a short but they are all correct. I bought a 15 amp hub with 4 outlets and have run leads to the battery charger, fridge, water-heater, washing machine, microwave, coffee-maker and toaster. All run normally. When it stops raining, I'll disconnect the thermostat leads to the water heater and see what gives. Until then, any suggestions are welcome please. Thanks in advance.
Found the problem. Paid an electrician to check the power-points and even he missed it. All 240volt "appliances" are added via their own electric cord and can be checked individually by simply plugging each cord into an external lead. So, the fridge, washing machine, etc all worked. Thanks to my wife, I missed one and that was the 240V stove-top element on the swift 500 series cook top. Its cord was plugged in behind the saucepan draw below the unit. (We do not have an oven). Switched off its power-point and presto, no more circuit-breaker tripping. No hurry to fix the element as we hardly ever use it. Thanks.