Sample context
Record where and how the sample was taken, how long the system had been operating and whether recent work could affect it.
Understanding an observation
Why is my radiator water black?
Dark or black heating water can be associated with corrosion products such as magnetite suspended in the sampled water. Colour alone does not establish the amount, location, cause or treatment required.
What to check next
Related checks
Consider turbidity alongside inhibitor and pH information rather than treating colour as a complete assessment.
System behaviour
Note heating performance, noise, circulation, leaks or pressure problems and seek appropriate professional investigation where needed.
What black water does not prove
It does not by itself prove that the entire system is full of sludge, identify a failing component or show that power flushing, chemicals or replacement work is necessary.