Worcester Bosch Greenstar HE system (ZB 7-27 HE, ZB 11-27 HE)
System boiler, natural gas and LPG
Combustion figures
| Figure | Natural gas (G20) | LPG (G31) |
|---|---|---|
CO₂ at high rate More infoHide infoFrom Table 14 (MI 7.1), CO₂ reading at max. rated heat output, at the flue gas testing point (234) with the probe about 135 mm in. No tolerance given. Table 14 labels the natural gas row Natural gas type H (23). The technical data (MI 1.9, Table 2) gives the same figures for natural gas and propane. For a combustion check the MI uses chimney sweep mode, which runs at max. rated heat output or the set heating output (MI 7.2.1, 7.2.2). MI 7 says the setting is factory sealed at maximum and adjusting the rated and min. heat input isn’t necessary. | 9.5 % | 11.3 % |
CO₂ at low rate More infoHide infoFrom Table 14 (MI 7.1), CO₂ reading at min. rated heat output. No tolerance given. The technical data (MI 1.9, Table 2) gives the same figures. | 9.2 % | 11.0 % |
Maximum CO More infoHide infoMI 7.1 says that if the CO level is over 300 ppm the gas volumetric flow rate is too high, and to reduce the gas flow rate on the adjustable gas flow restrictor (63) until the CO level is below 100 ppm. It says this after both the max. and min. rate CO₂ checks. The MI gives no other CO limit. |
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CO/CO₂ ratio | Not given in MI | Not given in MI |
O₂ | Not given in MI | Not given in MI |
Working inlet pressure More infoHide infoMI 7 says natural gas appliances must not be operated if the gas supply pressure is below 18 mbar or above 24 mbar, and LPG appliances must not be operated if the supply pressure is not 37 mbar. Checked at the testing point for gas supply pressure (7), which Fig. 3 (MI 1.7) shows on the gas valve. The MI doesn’t say whether the boiler should be running. Nominal gas supply pressure (MI 1.9, Table 2): NG G20 20 mbar, LPG 37 mbar. NG G20 appliances are factory set to Wobbe-Index 15 kWh/m³ and 20 mbar supply pressure and sealed (MI 7). |
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Gas rate at maximum More infoHide infoMaximum gas flow rate after 10 minutes from lighting (MI 1.9, Table 2), for NG G20 at 9,5 kWh/m³ and LPG at 12,9 kWh/kg (printed with decimal commas). Table 18 (MI 9.3) gives a NG gas volume flow rate of 48.1 l/min at display code 100 (27.5 kW heat input). When setting the heating output, MI 6.2.6 says to measure the gas flow rate and compare it with the figures for the displayed code. | 2.9 m³/h | 2.1 kg/h |
Flue integrity More infoHide infoAt the testing point for combustion air (234.1) with the probe about 80 mm in, boiler in chimney sweep mode (MI 7.2.1). The MI words it as O₂ must not be less than 20,6 % and CO₂ must not exceed 0,2 %, and says this checks the gas tightness of a type C13 or C33 flue system. | O₂ ≥ 20.6% CO₂ ≤ 0.2% | O₂ ≥ 20.6% CO₂ ≤ 0.2% |
From 6 720 610 596 GB (02.05)
Enter service mode for high and low rate
High rate
- Note where both temperature controls are set. Hold the service button (spanner symbol) until the display shows – –.
- Turn the central heating temperature control until the display shows 2.0. After a short delay it shows the current mode (0. = normal).
- Turn the hot water temperature control until the display shows 2. for maximum. The display and service button flash.
- Or: hold the chimney sweep button until – – shows. Runs at maximum (or the Service Function 5.0 output) for 15 minutes; hold again to end.
Low rate
- Turn the hot water temperature control anti-clockwise until the display shows 1. for minimum. The display and service button flash.
Ending the test
- Turn the hot water temperature control anti-clockwise to the stop (display 0.), then hold the service button until [ ] shows.
- Set both temperature controls back to where they were.
Models and GC numbers
| Model | GC number | Gas |
|---|---|---|
| ZB 7-27 HE system | 41-311-49 | NG |
| ZB 11-27 HE | Not added yet | LPG |
Source: Worcester Greenstar HE system (ZB 7-27 HE system) wall mounted condensing boiler for central heating installation and servicing instructions, 6 720 610 596 GB (02.05).
Sections: Cover (GC number); 1.6 Layout of appliance; 1.7 Function; 1.9 Technical data; 6.2.6 Setting the heating output (Service Function 5.0); 7 Converting the appliance to different gas types (checking the gas supply pressure, Table 13 conversion kits); 7.1 Setting the gas/air ratio; 7.2.1 Testing the O₂ or CO₂ level in the combustion air; 7.2.2 Testing CO and CO₂; 9.3 Heating/hot water output settings (N.G.).
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.