Signs and symptoms to monitor:

• Small leakage:
• A slight drop in boiler water level (feed water consumption increases).
• A slight increase in the feed water flow/ make-up.
• A hissing/ steam sound in the boiler (steam escaping into the gas side).
• A slight increase in the boiler pressure/ temperature fluctuation.
• Moisture/ steam at the boiler casing/ inspection openings.
• Large leakage:
• A rapid drop in boiler water level (alarm/ low-level trip).
• A large increase in feed water flow.
• A loud steam/ water leak sound.
• Steam/ water escaping from the boiler casing, flue or stack.
• A drop in boiler pressure/ steam output.
• Possible water hammer/ vibration.
• A rise in the flue gas temperature (less heat absorbed) or a change in the gas analysis.

1. Isolate the boiler: Shut off the fuel/ firing, shut off the steam and feed water, and allow the boiler to cool and depressurise. Isolate the boiler from the steam/ water system.
2. Identify the leaking tube: Locate the leaking tube by inspection (steam/ water marks, or by pressurising the water side and observing). If the tube is within the tube bank, it is identified by the leak location/ by isolating sections.
3. Prepare the tube and plug: Clean the tube ends (inside) at the drum/ header. Select a suitable plug (a tapered/ threaded plug of the correct material, or a welded plug) of the correct size.
4. Fit the plug: Insert the plug into the tube end at the drum/ header and secure it - either by driving/ expanding a tapered plug, by screwing in a threaded plug, or by welding a plug over the tube end (as per the maker/ Class-approved method). The plug must be fitted at both ends of the tube (top and bottom) to isolate it completely.
5. Ensure the repair is secure: The plug must be tight and leak-free. For welded plugs, the weld must be sound and inspected. For mechanical plugs, the plug must be driven/ expanded to seal.
6. Pressure test: After plugging, carry out a hydraulic test (or a steam/ water test) to confirm the plugged tube is leak-tight and the boiler is safe.
7. Compliance: The plugging must comply with the maker's/ Class requirements; the number of plugged tubes is limited (a boiler with too many plugged tubes may need re-tubing). Record the plugging and, where required, obtain surveyor/ Class approval.
8. Return to service: Refill the boiler, bring it back on line, and monitor for any further leaks.