A five-minute test on a 250 kW installation
A new 250 kW condensing boiler in a warehouse plant room is fed by 60 m of 54 mm steel from a U40 meter with a 35 mm outlet. The installer isolated the boiler, connected a 0-20 mbar gauge to the test point, and did a five-minute tightness test at 20 mbar. There was no measurable drop, so the installation was purged and commissioned. Two weeks later staff smell gas near a screwed joint on the main run; leak detection fluid shows a small bubble. The installation records consist of a handwritten note saying 'tightness test OK, purged, boiler commissioned' and no installation volume, no test pressure, no purge volume and no gas rate. The plant room has a gas detector at high level, an emergency shut-off button at the door and a warning notice, but no documented emergency procedure.
1. Critique the tightness test and explain why it could have passed while a leak remained.
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A five-minute test at 20 mbar is a domestic-style test and is not adequate for a 250 kW installation with 60 m of 54 mm pipe. The installation volume is large, so the test duration and stabilisation period must be longer and the test pressure must follow the non-domestic procedure (IGE/UP/1). A 0-20 mbar gauge with coarse resolution may not show a small leak, and temperature changes during the test can mask or create a drop.
The test also needs the boiler isolated and all joints accessible; a screwed joint that later bubbles may have been weeping slowly. Passing a short test does not prove tightness. The correct approach is to calculate the installation volume, use the specified test pressure and duration, allow stabilisation, correct for temperature, use a suitable gauge and record the result. Any leak must be repaired and the test repeated.
2. Describe the correct tightness testing and purging approach for an installation of this size.
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For this size, follow IGE/UP/1: isolate the installation, determine volume, select test pressure and duration, connect a suitable gauge, allow stabilisation, record start and end pressure and temperature, and apply the allowable drop. If it fails, trace with leak detection fluid or a detector, repair, and repeat.
After a pass, purge with the correct procedure: calculate purge volume from pipe volume, use a gas detector at the purge point to confirm gas concentration, and never rely on time alone. Purge to a safe location, control ignition sources, and verify at the appliance. Commission the boiler: gas rate, inlet pressure, combustion analysis, safety controls, flueing and ventilation. The leak found two weeks later means the installation must be isolated, repaired, re-tested and re-commissioned; a second short test is not acceptable.
3. What documentation and handover information should have been produced, and why does it matter now?
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Records should include the installation volume calculation; test pressure, duration, start and end readings and temperature; gauge details and calibration; purge volume and method; gas rate and inlet pressure; combustion readings; appliance and control checks; ventilation and flue checks; emergency shut-off and detector tests; and the RGII completion documentation.
The handwritten note is inadequate because it cannot show whether the test was suitable or whether the purge was verified. It also leaves no baseline for the leak investigation. A handover file should identify the responsible installer, date, appliance details, and any limitations. The owner should receive the documentation and the emergency procedure. In a leak investigation, the records show what was and was not done, support insurance and regulatory notification, and allow the next engineer to isolate and repair safely.