Spillage test for an open-flued gas fire

Before lighting

1. Inspect the flue or chimney. It must be present, suitable in size and type for the fire, and clear. Look for nests, debris, soot, a collapsed or displaced liner and leakage. A decorative fuel-effect fire, for example, typically needs a generous open flue.
2. Check the terminal discharges clear of windows, doors and air vents, so products cannot be drawn back inside, and that it is unobstructed. A terminal guard, an open cage, is fitted where the terminal is low, accessible or at risk of damage.
3. Carry out the flue-flow check by the prescribed procedure, including any specified warming. Test smoke should discharge at the correct terminal without returning into the room or showing significant leakage along the chimney. Smoke emerging from another flue’s terminal indicates leakage between flues. Investigate an unsatisfactory result and rectify the cause before operating the fire.

With a pellet smoke test, a small wisp seen outside the chimney does not mean the test has failed. Judge it by the set assessment: forceful plumes or a large escape point to a fault that needs correcting and retesting. Any suspected leakage into occupied parts of a building needs investigation. The operating spillage check below has its own test conditions and acceptance criteria.

Operating spillage test

1. Follow the model's instructions for heat setting, warm-up, smoke position and any permitted repeat.
2. Close the room's windows and doors. Keep permanent ventilation clear.
3. Run the fire for the specified warm-up so the flue establishes its draught. Testing too soon can give a false result.
4. Place the smoke source where this fire's instructions specify. Some fires are checked at the fire opening or canopy; a model with a draught diverter may specify that opening instead. The smoke should move towards the flue, not escape into the room.
5. Check the fan and internal-door combinations that could depressurise the fire room most. Include room extract fans running at their maximum usable setting with the room door closed; test relevant fans elsewhere with connecting doors open or closed as the layout demands. A cooker hood or tumble dryer can upset a natural draught even from another room.
6. Record the conditions tested and the result.

One model's procedure, for the BFM Gosford Plus inset live fuel effect fire, shows the detail to look for. Close the room's doors and windows, run the fire on high for about 5 minutes, then hold a smoke match 10 mm inside and below the centre of the canopy's lower front edge: most of the smoke should be drawn into the flue. If it spills, or there is doubt, repeat after a further 10 minutes. If it still spills with the restrictor baffle fitted, remove the baffle and retest once the fire has cooled. Spillage without the baffle means a flue fault, and a fault that cannot be traced means disconnecting the fire and getting expert advice. Where an extractor fan is nearby, repeat the test with the fan on maximum and the interconnecting doors open.

Reading the result

• A brief wisp before the specified warm-up is complete is different from a failed operating test. If smoke still comes back after warm-up and any repeat allowed by the instructions, combustion products are entering the room; they may contain carbon monoxide.
• Do not call continuing spillage harmless downdraught, or keep repeating until it disappears.
• A pass with the extractor off does not cancel spillage when it runs under the test conditions. Uncorrected spillage from a flued appliance is Immediately Dangerous under the current unsafe-situations procedure. Warn the user, make the fire safe and investigate the cause; a low room CO reading does not clear the failure.

Common causes

Check both paths. The chimney can be obstructed, damaged or poorly sized; a blocked room vent can separately starve an open-flued fire of replacement air. Either fault can contribute to spillage, so inspect the flue route and the room air supply. Scorched or sooty marks near the fire are warnings to investigate, never to dismiss.

After a repair

Repeat the flue-flow check, then the spillage test, before the fire goes back into use.