Worcester Bosch Greenstar HE plus combi (ZWBR 7-28 HE plus, ZWBR 11-35 HE plus, ZWBR 11-28, ZWBR 14-35)
Combi, natural gas and LPG
Combustion figures
| Figure | Natural gas (G20) | LPG (G31) |
|---|---|---|
CO₂ at high rate More infoHide infoFrom Table 15 (ZWBR 7-28, CO₂ reading at max. rated heat output) and Table 16 (ZWBR 11-35, CO₂ reading at max. and min. rated heat output) in MI 8.1. Measured at the flue gas testing point (234) with the probe about 135 mm in, with service function 2.0 set to operating mode Max. No tolerance given. In MI 8.1 the outer case is removed before setting and refitted at the end. The MI doesn’t say how long the boiler should run before measuring. Tables 15 and 16 list the gases as Natural gas type and LPG (Table 16: LPG (Propan)) under the size headings ZWBR 7-28 and ZWBR 11-35. The technical data (MI 1.9, Table 2) gives the same figures, with the LPG figures under ZWBR 11-28 Propane (11.3 %) and ZWBR 14-35 Propane (11.0 %). MI 8 says the setting is factory sealed at maximum, adjustment to the rated heat input and min. heat input is not necessary, and 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. MI 8.1 says to adjust the gas flow restrictor (63) to the CO₂ level given in Table 15; it doesn’t mention Table 16. MI 7.3 refers to 8.1. MI 9.2 says the combustion performance must be checked before and after any servicing work on the combustion and burner components (refer to section 8.2), and MI 9.3.7 says to recheck the combustion performance as described in 8.1 after fitting a new gas valve. MI 5.1 (Commissioning) has no combustion check. |
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CO₂ at low rate More infoHide infoFrom Table 15 (ZWBR 7-28, CO₂ reading at min. rated heat output) and Table 16 (ZWBR 11-35, one figure for max. and min. rated heat output) in MI 8.1, with service function 2.0 set to operating mode Min. Same for both sizes. No tolerance given. MI 8.1 says to adjust the CO₂ at min. on the gas valve adjusting screw (64) to the figure given in Table 15 for min. rated heat output, then recheck the levels at min. and max. rated heat output. The technical data (MI 1.9, Table 2) gives the same figures. | 9.2 % | 11.0 % |
Maximum CO More infoHide infoFrom MI 8.1, printed after both the max. and the min. CO₂ steps: measure the CO level; if the CO level is over 300 ppm, the gas volumetric flow rate is too high; reduce the gas flow rate on the adjustable gas flow restrictor (63) until the CO level is below 100 ppm at ZWBR 7-28 and below 200 ppm at ZWBR 11-35, then re-adjust the CO₂ level if necessary. The MI gives these limits by size only, not by gas type, using the same size names as Tables 15 and 16, which cover both gases, so they’re shown for both. The MI doesn’t say what to do if the CO is between the 100 or 200 ppm figure and 300 ppm, so both figures are shown as printed. MI 8.2.2 (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 figure; the step itself is printed as CO- and CO₂ levels, with the verb missing. |
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CO/CO₂ ratio | Not given in MI | Not given in MI |
O₂ More infoHide infoThe only O₂ figure in the MI is for the combustion air (see Flue integrity). | Not given in MI | Not given in MI |
Working inlet pressure More infoHide infoMI 8 (Checking the gas supply pressure, page 34) says to check the gas supply pressure at the gas supply pressure testing point, and that 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. The testing point for gas supply pressure is item 7 in Figs. 2 and 3 (MI 1.6, 1.7); Fig. 3 shows it on the gas valve (56). The MI doesn’t say whether the boiler should be running. MI 5.1 says the gas supply pressure must be tested before commissioning. Gas supply pressure in the technical data (MI 1.9, Table 2): natural gas G20 20 mbar, LPG 37 mbar. Appliances for natural gas type G20 are factory set to Wobbe-Index 15 kWh/m³ and 20 mbar supply pressure and sealed (MI 8). The MI gives no meter or regulator figure. |
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Gas rate at maximum More infoHide infoMaximum gas flow rate after 10 minutes from lighting (MI 1.9, Table 2), natural gas G20 (HiB = 9,5 kWh/m³) and LPG (Hi = 12,8 kWh/kg). Table 2 prints the LPG figures under ZWBR 11-28 Propane (2.2 kg/h) and ZWBR 14-35 Propane (2.5 kg/h). The natural gas output settings tables give a gas vol. flow rate at display code 100 of 49.9 l/min for the ZWBR 7-28 (Table 20, MI 10.3) and 62.1 l/min for the ZWBR 11-35 (Table 22, MI 10.5); the LPG tables (Tables 21 and 23, MI 10.4 and 10.6) give no gas flow rate. When setting the heating output (Service Function 5.0), MI 7.2.4 says to measure the gas flow rate and compare it with the figures for the code number shown. |
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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 8.2.1). The MI words it as the O₂ level must not be less than 20,6 % and the CO₂ level must not exceed 0,2 %, and says this checks the gas tightness of a type C13 or C33 flue system. In chimney sweep mode the appliance switches to max. rated heat output or the set heating output, and there are 15 minutes in which to measure. | O₂ ≥ 20.6% CO₂ ≤ 0.2% | O₂ ≥ 20.6% CO₂ ≤ 0.2% |
From 6 720 610 597 GB (01.07)
Enter service mode for high and low rate
High rate
- On the text display press any button, then use ▲ ▼ and ▶ to go to Settings, Service, Display service parameters.
- Hold ▶ for about 5 seconds until Adjust service parameters and 2.0, Operating mode show.
- Press ▶, choose Max with ▲ or ▼, press ▶, then at Store settings? choose yes and press ▶.
- Or: hold the Chimney sweep button until the display shows – –. The button lights. It runs at maximum, or at the set heating output if limited.
Low rate
- At 2.0, Operating mode press ▶, choose Min with ▲ or ▼, press ▶, then store with yes and ▶.
Ending the test
- Set 2.0, Operating mode back to Normal the same way, then press ↩ to leave the menu.
- Chimney sweep: hold the Chimney sweep button until – – shows. It also ends by itself after 15 minutes.
Models and GC numbers
| Model | GC number | Gas |
|---|---|---|
| ZWBR 7-28 HE plus | 47-311-56 | NG |
| ZWBR 11-35 HE plus | 47-311-57 | NG |
| ZWBR 11-28 LPG (ZWBR 7-28 size) | Not added yet | LPG |
| ZWBR 14-35 LPG (ZWBR 11-35 size) | Not added yet | LPG |
Source: Worcester Greenstar HE plus combi (ZWBR 7-28 HE plus, ZWBR 11-35 HE plus) wall mounted condensing boiler for central heating and mains fed domestic hot water installation and servicing instructions, 6 720 610 597 GB (01.07).
Sections: Cover (GC numbers); 1.6 Layout of appliance (Fig. 2); 1.7 Function (Fig. 3); 1.9 Technical data (Table 2); 5.1 Commissioning; 7.2.4 Setting the heating output (Service Function 5.0); 7.3 Setting the gas/air ratio; 8 Converting the appliance to different gas types (checking the gas supply pressure, Table 14 conversion kits); 8.1 Setting the gas/air ratio (Tables 15 and 16); 8.2.1 Testing the O₂ or CO₂ level in the combustion air; 8.2.2 Testing CO and CO₂; 9.2 Description of servicing operations; 9.3.7 Gas valve; 10.3–10.6 Heating/hot water output settings (Tables 20 to 23).
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.