Worcester Bosch R 25 & 30 HE combi (ZWB 7-25 R 25 HE, ZWB 7-30 R 30 HE)
Combi, natural gas, or LPG with a conversion kit
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, with the testing probe about 135 mm into the flue gas testing point (234). No tolerance given. Table 16 labels the gases Natural gas type G20 and LPG G31 (propane). In MI 7.1 the outer case is removed before the readings are taken and refitted at the end. The MI doesn’t say how long after firing to measure. The technical data (MI 1.9, Table 2) gives the same figures for R 25 HE and R 30 HE. MI 5.1 says the operational CO₂ level is set at the factory and no adjustment is necessary when installing a natural gas fired appliance. MI 7.1 says the gas/air ratio may only be adjusted on the basis of a CO₂ measurement at max. heat output and min. heat output using an electronic tester. MI 6.3 says adjustment is only required where the appliance has been stripped down and assembled, the fan, burner or gas valve replaced, or the appliance converted to a different gas type. MI 8.2 says the combustion performance must be checked before and after any servicing work on the combustion and burner components, and MI 8.3.7 says to recheck it after fitting a new gas valve (both refer to MI 7.1). The MI covers LPG by conversion from N.G to L.P.G with a conversion kit (MI 7, Table 15). | 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, Table 2) gives the same figures for R 25 HE and R 30 HE. | 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 More infoHide infoThe only O₂ figure in the MI is for the combustion air check (MI 7.2.1); see Flue integrity. | Not given in MI | Not given in MI |
Working inlet pressure More infoHide infoMI 5.1 says that before commissioning the gas supply pressure must be checked at the gas supply pressure test point (Fig. 2, item 7); Fig. 3 (MI 1.7) shows testing point 7 on the gas valve. MI 5.1 and MI 7 say natural gas appliances must not be operated if the gas supply pressure is below 18 mbar or above 24 mbar. For LPG, MI 7 says the appliance must not be operated if the supply pressure is below or above 37 mbar; MI 5.1 words it as must not be operated if the supply pressure is not 37 mbar at the inlet to the appliance. The MI doesn’t say whether the boiler should be running. 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 7). The MI gives no meter or regulator figure. |
|
|
Gas rate at maximum More infoHide infoMaximum gas flow rate after 10 minutes from lighting (MI 1.9, Table 2), natural gas G20 at CVnet 34.02 MJ/m³ and LPG at CVnet 88 MJ/m³. Table 2 heads its columns R 25 HE and R 30 HE, each for Natural gas and Propane. Max. rated heat input net: R 25 HE 27.5 kW, R 30 HE 29.5 kW (both gases). The natural gas output settings table (MI 9.3, Table 20) gives a gas vol. flow rate of 51.6 l/min (at tV/tR = 80/60°C) at display code 100, with a heat input of 29.5 kW. Table 20 doesn’t say which model it’s for; 29.5 kW is the R 30 HE max. rated heat input in Table 2, and there is no separate R 25 HE table. The propane table (MI 9.4, Table 21) gives no gas flow rate. When setting the heating output (Service Function 5.0), MI 6.2.5 says to measure the gas flow rate and compare it with the figures for the code number displayed. |
|
|
Flue integrity More infoHide infoAt the combustion air testing point (234.1) with the probe about 80 mm in, boiler in chimney sweep mode, which runs at max. rated heat output or the set heating output (MI 7.2.1). The MI words it as O₂ level must not be less than 20,6 % and CO₂ level 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 6 720 611 441 GB (05.04)
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 CH temperature control (radiator symbol) until the display shows 2.0. After a short delay it shows 0.
- Turn the hot water temperature 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 set heating output) for 15 minutes; hold it again to end.
Low rate
- Turn the hot water temperature control anti-clockwise until the display shows 1. for minimum.
- Turn it back to 2. to go back to maximum.
Ending the test
- Turn the hot water temperature control anti-clockwise to the stop (display 0.), then hold the service button until the display shows [ ].
- Set both temperature controls back to where they were. Display goes back to the CH flow temperature.
Models and GC numbers
| Model | GC number | Gas |
|---|---|---|
| ZWB 7-25 R 25 HE combi | 47-311-77 | NG |
| ZWB 7-30 R 30 HE combi | 47-311-78 | NG |
Source: Worcester R 25 & 30 HE combi wall mounted condensing boiler for central heating and mains fed domestic hot water installation and servicing instructions, 6 720 611 441 GB (05.04).
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; 6.2.5 Setting the heating output (Service Function 5.0); 6.3 Setting the gas/air ratio; 7 Converting the appliance to different gas types (checking the gas supply pressure, Table 15 conversion kits); 7.1 Setting the gas/air ratio (Table 16); 7.2.1 Testing the O₂ or CO₂ level in the combustion air; 7.2.2 Testing CO and CO₂; 8.2 Description of servicing operations; 8.3.7 Gas valve; 9.3 Heating/hot water output settings (N.G) (Table 20); 9.4 Heating/hot water output settings (L.P.G) (Table 21).
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.