Can anyone think of a powder / crystalline substance I can use to try and prove an intermittent small water leak. I want something that will positively change colour if wetted, but doesn't change just left in the atmosphere.
I am trying to convince myself that an automatic air vent on an oil fired boiler is the cause of a loss of system pressure by leaking when it shouldn't. I would just change the thing - they are only about £10, but it is in a very inaccessible position so that is not an easy option. However I can sprinkle a powder on it from above!