Worcester Bosch Checked against MI

Worcester Bosch Greenstar 4000 system (GR4700iW 24 S, 21 S, 18 S, 15 S, 12 S)

System boiler, natural gas and LPG

Combustion figures

Figure	Natural gas (G20)	LPG (G31)
CO₂ at high rate More infoHide info Boiler at maximum in chimney sweep mode, combustion cover on, measured 10 minutes after firing, at the flue gas sample point. The technical data (MI 13.1) gives NG 9.4% and LPG 10.8% for every size.	Between 9.0 and 9.8%	Between 10.4 and 11.0%
CO₂ at low rate More infoHide info Boiler at minimum in chimney sweep mode, combustion cover on, allowed to stabilise, measured 10 minutes after firing. The technical data (MI 13.1) gives NG 8.6% and LPG 10.2% for every size.	A minimum of 0.2 lower than the maximum reading taken and between 8.2 and 9.0%	A minimum of 0.2 lower than the maximum reading taken and between 10.0 and 10.4%
Maximum CO More infoHide info The manual doesn’t agree with itself. The commissioning flow chart (MI 6.8, Fig. 67) uses CO < 350 ppm at maximum and minimum. The service table (MI 8.5, Table 30) gives <250 ppm at maximum and minimum.	Commissioning <350 ppm Service <250 ppm	Commissioning <350 ppm Service <250 ppm
CO/CO₂ ratio More infoHide info From the commissioning flow chart (MI 6.8, Fig. 67), at maximum and minimum. MI 6.6 refers to the technical data for CO/CO₂ ratios, but the technical data tables don’t list one.	<0.004	<0.004
O₂	Not given in MI	Not given in MI
Working inlet pressure More infoHide info Boiler at maximum in chimney sweep mode, with heat taken away through the radiators and a hot water outlet open. At the meter: NG 19–23 mbar. At the LPG storage: 32–45 mbar. Allowed drops: across the pipework NG 1 mbar, LPG 2.5 mbar; across the appliance 1.5 mbar. Fig. 66 splits the LPG drop into 0.5 mbar from storage to regulator and 2.0 mbar from regulator to appliance inlet.	Appliance inlet 18–22 mbar Gas valve test point 16.5–20.5 mbar	Appliance inlet 29.5–42.5 mbar Gas valve test point 28–41 mbar
Gas rate at maximum More infoHide info 10 minutes from lighting, from the technical data (MI 13.1). Measure at the meter after at least 10 minutes at maximum in service mode, with all other gas appliances off. Where there’s no meter (e.g. LPG), check CO/CO₂ instead (MI 6.6).	24 S 2.61 m³/h 21 S 2.28 m³/h 18 S 1.95 m³/h 15 S 1.63 m³/h 12 S 1.30 m³/h	24 S 1.91 kg/h 21 S 1.68 kg/h 18 S 1.43 kg/h 15 S 1.19 kg/h 12 S 0.95 kg/h
Flue integrity More infoHide info At the air inlet sample point on the flue turret/adaptor, combustion casing on, boiler at maximum in chimney sweep mode (MI 6.9). The text in 6.9 lists both readings, but the flow chart (Fig. 67) says O₂ ≥ 20.6% or CO₂ < 0.2%.	O₂ ≥ 20.6% CO₂ < 0.2%	O₂ ≥ 20.6% CO₂ < 0.2%

From 6 720 891 162 (2020/09)

Enter service mode for high and low rate

High rate

Open a hot water outlet so the boiler doesn’t shut down on high temperature during the test.
Open the radiator valves and any zone valves so there’s heat transfer.
Press and hold ok for 5 seconds until Chimney sweep is displayed.
An alert message appears. Once you’ve read and understood it, press ok to confirm.
The boiler enters chimney sweep mode and goes to maximum on its own. The display alternates 100% with the flow temperature.
It takes about 30 to 35 seconds to ramp up to maximum.
Chimney sweep mode runs both the heating and hot water circuits. Run enough hot water that the boiler doesn’t overheat.
With the internal diverter valve kit fitted: at 74°C or below the valve sits in mid position and both circuits run, so draw enough hot water that the boiler doesn’t cycle on low demand. At 75°C it switches to heating only, and goes back to mid position at 65°C or below.
Without the internal diverter valve, the MI recommends putting any external diverter valve in the central heating position.
Run for at least 10 minutes at maximum before measuring the gas rate or CO₂.

Low rate

With the boiler already in chimney sweep mode at maximum, press ▼ (down) to set minimum.
The setting is accepted after 2 seconds and marked with a tick. The display alternates the minimum percentage with the flow temperature.
It takes about 30 to 35 seconds to ramp down. Wait a further 30 seconds for it to stabilise at minimum before taking readings.
To go back to maximum, press ▲ (up) for 100%.

Ending the test

Press ok or ↩ (back) to return to normal operation.
Chimney sweep mode ends on its own after 15 minutes. Re-enter it if you need more time.
After exiting, the pump keeps running to cool the heat exchanger and status code 208 shows.

Models and GC numbers

Model	GC number	Gas
GR4700iW 24 S NG	41-800-15	NG
GR4700iW 21 S NG	41-800-13	NG
GR4700iW 18 S NG	41-800-11	NG
GR4700iW 15 S NG	41-800-09	NG
GR4700iW 12 S NG	41-800-07	NG
GR4700iW 24 S LPG	41-800-16	LPG
GR4700iW 21 S LPG	41-800-14	LPG
GR4700iW 18 S LPG	41-800-12	LPG
GR4700iW 15 S LPG	41-800-10	LPG
GR4700iW 12 S LPG	41-800-08	LPG

Source: Greenstar 4000 GR4700iW S gas-fired condensing system appliance installation and maintenance instructions, 6 720 891 162 (2020/09).

Sections: 3.3 Appliance type overview; 6.4 Chimney sweep mode; 6.5 Checking gas inlet pressure; 6.6 Checking the gas rate; 6.8 CO and combustion check; 6.9 Checking flue integrity; 6.10 Flue gas analysis; 8.5 Flue gas analysis; 8.8 Setting the air/gas ratio; 13.1 Technical data.

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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.