We were engaged to locate a leak on a sprinkler system at a Bristol factory. The sprinkler pumps were running continuously due to a significant, system pressure loss but there were no visible signs of a leak/loss anywhere. A step test was conducted by others which appeared to highlight the area of the leak but attempts to pinpoint the leak within that area failed. It eventually transpired that the step test results were invalid due to the integrity of the valves not being 100%. The test was repeated using alternative valves and this proved the leak to be on a different section of the site. Acoustic detection was used and the leak was identified in the tarmac roadway.