Vaillant ecoTEC plus 938 combi (938, VUI GB 386/5-5 A)
Combi with 15 litre shift-load cylinder, natural gas and LPG
Combustion figures
| Figure | Natural gas (G20) | LPG (G31) |
|---|---|---|
CO₂ at high rate More infoHide infoAfter 5 minutes at full load in check programme P.01, measured at the flue gas analysis point. Adjust to the front casing removed figure. |
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CO₂ at low rate More infoHide infoThe MI gives CO₂ at full load only. It has a minimum load check programme (P.02) but no low rate figure. | Not given in MI | Not given in MI |
Maximum CO More infoHide infoThe full load figure is from the MI 7.15.5 table. The Benchmark flowchart in Appendix G checks CO at both maximum and minimum rate against less than 350 ppm. One box on that flowchart says 335 ppm instead, which looks like a misprint. |
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CO/CO₂ ratio More infoHide infoThe full load figure is from the MI 7.15.5 table. The Benchmark flowchart in Appendix G checks the ratio at both maximum and minimum rate against less than 0.004. |
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O₂ at high rate More infoHide infoAfter 5 minutes at full load with the front casing closed. | 4.5% ± 1.8 | 5.1% ± 0.8 |
O₂ at low rate | Not given in MI | Not given in MI |
Working inlet pressure More infoHide infoMeasured at the measuring nipple (lower screw) on the gas valve, boiler at full load in check programme P.01, with all other gas appliances working. The MI also gives these as 1.3–2.3 kPa (NG) and 2.3–4.3 kPa (LPG). Technical data gives a nominal gas flow pressure of 20.0 mbar (NG) and 37.0 mbar (LPG). |
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Gas rate at maximum More infoHide infoFrom technical data: at 15 °C and 1013 mbar, based on hot water generation. MI 7.15.3 also has a gas flow rate table to check at the meter, set out by nominal heat output rather than by model. Its 38 kW row gives H gas 4,15 m³/h (+5% 4,36, −10% 3,73) and P gas 3,05 kg/h (+5% 3,20, −10% 2,75). | 4.2 m³/h | 3.1 kg/h |
Flue integrity More infoHide infoAt the air inlet test point, boiler at maximum rate (Benchmark flowchart, Appendix G). | O₂ ≥ 20.6% CO₂ < 0.2% | O₂ ≥ 20.6% CO₂ < 0.2% |
From 0020209593_01 (08.11.2016)
Enter service mode for high and low rate
High rate
Steps not added yet. Follow the MI.
Low rate
Steps not added yet. Follow the MI.
Ending the test: follow the MI.
Models and GC numbers
| Model | GC number | Gas |
|---|---|---|
| ecoTEC plus 938 (VUI GB 386/5-5 A) | 47-044-61 | NG |
Source: Vaillant ecoTEC plus VUI installation and maintenance instructions, 0020209593_01 (08.11.2016).
Sections: 2.3 Validity of the instructions; 5.1.1 Information on liquid gas operation; 7.7 Using check programmes; 7.15.3 Checking the gas flow rate; 7.15.4 Checking the gas flow pressure; 7.15.5 Checking the CO2 content and, if necessary, adjusting it; G Commissioning Checklist (Benchmark flowchart); K Technical data.
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.