We've got a 2 year old double bunded plastci 1200ltr oil tank with a Watchman remote sensor which is flashing alternately the quantity in the tank and a small "c" on the display and the red light is on permanently. Also using oil very rapidly ( appx 100litres a week for a Rayburn 680) but this is prob due to the weather rather than a leak. Talked to the tank supplier who suggested it's the battery in the sensor & claims that they've discontinued that unit so no batteries available ( ?! in 2 yr old unit) & to contact Watchman in northern ireland. Done that - they said indicator is saying moisture ( condensation from cold weather/water/oil) is present in the bund between the inner tankl and outer skin & this needs checking first. Now trying to get the tank supplier ( local firm ) to come and check it out but no response as yet to 2 days of phone calls. Is there any way I can check what is in the bund & whether we have a big/medium or small problem ?