Worcester Bosch Greenstar 24/28/30 combi (24 kW, 28 kW, 30 kW)
Combi, natural gas
Combustion figures
| Figure | Natural gas (G20) |
|---|---|
CO₂ at high rate More infoHide infoFrom Table 25 (MI 8.5), for natural gas H (23), boiler at maximum rated output. Table 25 gives no time; MI 8.4 says to run the boiler at maximum for at least 10 minutes before measuring CO. The ± 0.5 tolerance is for checking an existing appliance. After cleaning or replacing parts, or when adjusting because the reading is outside the tolerance, it is ± 0.3 at maximum. The manual doesn’t agree with itself for the 30 kW: the technical data (MI 2.3, Table 6) gives 9.6% for the 24 and 28 but 9.8% for the 30, after 30 minutes, while Table 25 gives one figure for all sizes. The air/gas ratio valve is factory set and must not be adjusted during commissioning unless the Worcester help line recommends it (MI 6.9). | 9.6% ± 0.5 |
CO₂ at low rate More infoHide infoFrom Table 25 (MI 8.5), boiler at minimum rated output. The ± 0.5 tolerance is for checking an existing appliance. After cleaning or replacing parts, or when adjusting because the reading is outside the tolerance, it is ± 0.4 at minimum. The technical data (MI 2.3, Table 6) gives 8.7% for the 24 and 28 but 8.8% for the 30, after 30 minutes. | 8.7% ± 0.5 |
Maximum CO More infoHide infoThe manual gives two limits. The combustion check flow chart (MI 6.9, Fig. 51) says CO < 350ppm at maximum and minimum rate. Table 25 (MI 8.5) and MI 8.4 say less than 200 ppm. The MI doesn’t say which takes priority. |
|
CO/CO₂ ratio More infoHide infoThe manual gives two limits. The combustion check flow chart (MI 6.9, Fig. 51) says CO/CO₂ ratio < 0.004 at maximum and minimum rate. Table 25 (MI 8.5) and MI 8.4 give 0.002 in brackets after the CO limit: CO - less than 200 ppm (0.002 ratio). |
|
O₂ | Not given in MI |
Working inlet pressure More infoHide infoFrom Table 24 and Fig. 60 (MI 8.1), with the boiler at maximum rated output using the Central Heating boost button, and all other gas appliances working. At the meter: 19–23 mbar. Allowed drop: 1 mbar across the pipework, 1.5 mbar across the boiler. The MI says the appliance must not be operated if the pressure is above or below these figures. |
|
Gas rate at maximum More infoHide infoMax. 10 minutes from lighting, natural gas G20 (MI 2.3, Table 6, where the sizes are headed 24, 28 and 30). The MI gives no separate gas rate check steps. Table 6 gives a central heating max. rated heat output at 80/60 of 20.3 kW for every size, and a hot water max. rated heat input of 24.6, 28 and 30 kW. |
|
Flue integrity More infoHide infoAt the air inlet sample port on the flue, boiler at maximum rated output, readings allowed to stabilise (MI 8.3), and in the combustion check flow chart (MI 6.9, Fig. 51). MI 8.3 words it as the O₂ level must exceed 20.6% and the CO₂ level must not exceed 0.2%. | O₂ ≥ 20.6% CO₂ < 0.2% |
From 6 720 811 922 (2014/07)
Enter service mode for high and low rate
High rate
- Hold the Central Heating boost button until it lights. Display shows a middle and bottom bar on each digit (set maximum heating output).
- Press the Central Heating boost button again for maximum rated output. Display shows three bars on each digit.
Low rate
- Press the Central Heating boost button again for minimum. Display shows a bottom bar on each digit.
Ending the test
- Press the Central Heating boost button again until its light goes out. Display shows only the flow temperature.
- It goes back to normal by itself after 15 minutes.
Models and GC numbers
| Model | GC number | Gas |
|---|---|---|
| Greenstar 24 kW | 47-406-54 | NG |
| Greenstar 28 kW | 47-406-56 | NG |
| Greenstar 30 kW | 47-406-64 | NG |
Source: Greenstar 24/28/30 wall hung RSF gas fired condensing combination boiler installation, commissioning and servicing instructions, 6 720 811 922 (2014/07).
Sections: Cover (GC numbers); 2.3 Technical data; 6.9 CO and combustion checks; 8.1 Checking the gas supply pressure; 8.2 Check flue integrity (Central Heating boost button); 8.3 Checking flue system for tightness; 8.4 Measuring CO content of flue gas; 8.5 Setting gas/air ratio (CO2).
Spotted something wrong? Tell us.
Check these figures against the MI for the appliance in front of you, matched by GC number and manual date. Combustion work needs a calibrated analyser and a Gas Safe registered engineer.