Worcester Bosch Greenstar HE combi (ZWB 7-25 HE, ZWB 7-30 HE, ZWB 11-25 HE, ZWB 11-30 HE)
Combi, natural gas and LPG
Combustion figures
| Figure | Natural gas (G20) | LPG (G31) |
|---|---|---|
CO₂ at high rate More infoHide infoFrom Table 16 (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 16 labels the gases Natural gas type G20 and LPG G31 (propane). The technical data (MI 1.9 Table 2 and MI 1.10 Table 3) gives the same figures for both sizes. MI 5.1 says the operational CO₂ level is set at the factory and no adjustment is necessary when installing a natural gas appliance. MI 7.1 says the gas/air ratio may only be adjusted on the basis of a CO₂ measurement at max. and min. heat output using an electronic tester. | 9.2 % | 10.8 % |
CO₂ at low rate More infoHide infoFrom Table 16 (MI 7.1), CO₂ reading at min. rated heat output. No tolerance given. The technical data (MI 1.9 and 1.10) gives the same figures. | 8.8 % | 10.5 % |
Maximum CO More infoHide infoMI 7.2.2 (Testing CO and CO₂) says to take the reading at the flue gas testing point (234) with the probe about 135 mm in, in chimney sweep mode, but gives no CO limit. The step itself is printed as CO- and CO₂ levels, with the verb missing. | Not given in MI | Not given in MI |
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 (Checking the gas supply pressure) 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 below or above 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. Gas supply pressure in the technical data (MI 1.9, 1.10): 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 and MI 1.10 Table 3), NG G20 at CVnet 34.02 MJ/m³ and LPG at CVnet 88 MJ/m³. The MI heads these tables ZWB 7/11-25 (ZWB 7-25 natural gas, ZWB 11-25 propane) and ZWB 7/11-30 (ZWB 7-30, ZWB 11-30). The natural gas output settings tables give a gas volume flow rate at display code 100 of 48.1 l/min for the ZWB 7-25 (Table 20, MI 9.3) and 51.6 l/min for the ZWB 7-30 (Table 22, MI 9.5). 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. |
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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 6 720 610 576 GB (03.02)
Enter service mode for high and low rate
High rate
- Hold the service button (spanner symbol) until the display shows – – and the button lights up.
- Turn the central heating control (radiator symbol) until the display shows 2.0. After a short delay it shows the current mode (0. = normal).
- Turn the hot water control (tap symbol) 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 control anti-clockwise until the display shows 1. for minimum. The display and service button flash.
Ending the test
- Turn the hot water control anti-clockwise to the stop (display 0.), then hold the service button until [ ] shows.
- Set both temperature controls back to where they were. The display goes back to the flow temperature.
Models and GC numbers
| Model | GC number | Gas |
|---|---|---|
| ZWB 7-25 HE combi | 47-311-73 | NG |
| ZWB 7-30 HE combi | 47-311-74 | NG |
| ZWB 11-25 HE combi | Not added yet | LPG |
| ZWB 11-30 HE combi | Not added yet | LPG |
Source: Worcester Greenstar HE combi (ZWB 7-25 HE combi, ZWB 7-30 HE combi) wall mounted condensing boiler installation and servicing instructions, 6 720 610 576 GB (03.02).
Sections: Cover (GC numbers); 1.7 Function (Fig. 3); 1.9 Technical data ZWB 7/11-25; 1.10 Technical data ZWB 7/11-30; 5.1 Commissioning; 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 15 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; 9.3–9.6 Heating/hot water output settings.
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.