Spillage and a poor CO/CO₂ ratio at an annual service
You attend an annual service on a 15-year-old open-flued natural gas boiler (rated 18 kW) in the utility room of a 1970s bungalow. The room has a louvred door and a 100 cm² permanent wall vent. During last year's renovation the householder fitted a decorative grille over the vent and packed the gap behind it with foam draught excluder, and a 60 l/s kitchen extractor was installed in the adjoining open-plan kitchen. On test the flame is long and yellow with slight lift. Combustion analysis at the flue sampling point reads CO/CO₂ ratio 0.0075 and 190 ppm CO. Your spillage test at the draught diverter shows products escaping into the room after about four minutes with the extractor running and the utility door closed. The CO alarm is in the hallway, 6 m away, and has not sounded. The occupier mentions headaches and that "the boiler smells sometimes when the extractor is on". The property is rented and the letting agent booked the service.
1. Classify the situation and justify the classification against the readings and the spillage result.
Read the worked answer
This is Immediately Dangerous (ID) - the appliance must not be left operating.
The classification rests on more than one independent indicator:
- Spillage of products into the room during a valid test. Products escaping at the draught diverter into an occupied room is the defining ID condition for an open-flued appliance; it does not require a smell or a sounding alarm.
- CO/CO₂ ratio 0.0075. For natural gas the accepted threshold for acceptable combustion is 0.004; 0.0075 is approaching double that and confirms incomplete combustion, consistent with the yellow, lifting flame. (For LPG the comparable threshold is 0.008, which shows how far out this natural gas reading is.)
- 190 ppm CO in the sample reinforces the combustion analysis; it is not itself the classification criterion, but it corroborates it.
- The measured cause is real and ongoing - the permanent ventilation has been deliberately blocked with foam, and a 60 l/s extractor in the adjoining space depressurises the room and competes with the draught diverter.
- The non-sounding hallway alarm is irrelevant. A CO alarm is not a test instrument and its location means it would respond late, if at all, to a room-local problem.
Reported headaches make the urgency human, not merely technical: advise the occupier to seek medical advice if symptoms persist or worsen.
2. List, in order, the immediate actions you take at the property, including what you attach, who you tell and what you do about the boiler's gas supply.
Read the worked answer
- Make the appliance safe first - turn the boiler off at its controls and isolate it at its service valve. Where the appliance cannot be made safe by isolation alone, disconnect and cap the supply; do not leave it capable of being relit by the occupier.
- Deal with the ventilation and the extractor - explain that the foam must come out of the permanent vent and the grille must give the full 100 cm² free area, and that until the combustion air and flue performance are verified, the boiler stays off. (Removing the foam yourself is a repair, not a check: it does not by itself prove the boiler is safe.)
- Attach a "Danger - Do Not Use" warning label to the appliance, in a visible position, and where practicable advise the occupier not to use it and to ventilate the room.
- Inform the person responsible - the occupier verbally and the letting agent/landlord in writing, describing the defect, the action taken and what is required before re-use.
- Document and report - complete the unsafe situation record (appliance details, readings, spillage result, ventilation defect, action taken, warning notice issued) and notify RGII in accordance with the unsafe situations procedure.
- Escalate if there is any smell of gas - treat that as a gas escape: no switches or naked flames, open windows, operate the ECV, and call the Gas Networks Ireland emergency line.
- Arrange the return visit only after the ventilation is restored and the boiler has been serviced/repaired.
3. What must be demonstrated before the warning notice can be removed and the boiler returned to service?
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The notice comes off only when the cause has been corrected and the appliance has been proven safe under the conditions that produced the failure - not when the room simply "smells better".
- Restore permanent ventilation to at least 100 cm² free area (verify the actual free area of the grille, not the nominal size), and confirm the extractor does not cause unacceptable depressurisation of the room with doors in the normal position. If the two cannot coexist, the extractor's use and the boiler's air supply must be resolved - the boiler needs a reliable air path.
- Service and repair the boiler - clean the heat exchanger, burner and injectors, check the draught diverter and flue for integrity and obstruction, and confirm the flue is sound and correctly terminated.
- Prove the flue - flue flow/ smoke test to confirm the flue pulls, followed by a spillage test at the draught diverter with the extractor running, doors closed and any other fans operating, held for the full test period with no spillage.
- Prove combustion - combustion analysis with the CO/CO₂ ratio comfortably back below 0.004 for natural gas, CO within acceptable limits, correct gas rate for an 18 kW appliance (roughly 1.66 m³/h at 39 MJ/m³) and a stable flame picture.
- Only then remove the warning label, record all readings and the corrective works, and re-issue documentation to the occupier and landlord. If the appliance cannot be brought back within limits, it stays off and the recommendation is replacement with a room-sealed appliance.