Commissioning is more than firing the boiler. A proper combi handover protects warranty, meets Building Regulations, and reduces callbacks. Use this checklist alongside the manufacturer’s Benchmark sheet and installation manual.
Before first start
- Installation matches manufacturer schematic — flue, condensate, gas, DHW, filling loop, filter, bypass.
- System flushed and cleaned per BS 7593 / Part L requirements on replacements.
- Corrosion inhibitor dosed; concentration to be tested at handover.
- Expansion vessel pre-charge verified (heating and external DHW vessel if fitted).
- Electrical supply, polarity, and earth correct; fused spur appropriately rated.
- Gas pipework sized for maximum input; meter capacity confirmed.
- Air removed from heating circuit; all radiators balanced initially.
- Pressure test completed before fill (typically ~3 bar held) per manufacturer / BS EN 14336.
Gas and combustion
- Gas rate checked at high fire — matches data badge for correct gas type (natural gas / LPG).
- Inlet gas pressure recorded at idle and at maximum demand.
- Combustion analysis at high and low fire (or minimum modulation point) — CO, CO2, ratio within manufacturer tolerances.
- Burner pressure or gas valve settings adjusted only per manufacturer procedure.
- Flue integrity and spillage test (where applicable) satisfactory.
Hydraulics and bypass
- System pressure set cold (typically 1.0–1.5 bar).
- Pump speed / mode set per instructions.
- External automatic bypass adjusted for minimum flow — not fully open unless specified.
- Internal bypass or pump logic confirmed on models without external bypass.
- Filter / dirt separator installed on return; de-aerator on flow where specified.
- No leaks at all joints under heat and pressure cycle.
Heating performance
- Maximum kW output limited in software if heat-loss calculation requires (avoid oversizing).
- Heating flow temperature set sensibly (often 55–65 °C for condensing operation — see flow temperature guide).
- Room thermostat and programmer wired and tested; TRVs open on at least one radiator when using bypass.
- OpenTherm or bus controls paired and modulating if fitted.
- Boiler Plus additional measure documented (weather comp, load comp, smart control, or FGHR).
Domestic hot water
- DHW temperature set and verified at tap — scalding risk assessed (TMVs where required).
- Hot-water flow rate and temperature rise checked against datasheet at representative outlet.
- DHW expansion vessel or shock arrestor commissioned where required.
- Diverter valve transitions heating ↔ hot water without fault.
- Limescale protection present on cold feed in hard-water areas.
Documentation and notification
- Benchmark checklist completed in full and left with appliance.
- Building Regulations notification via Competent Person Scheme or local authority.
- Gas Safe certificate / job record provided.
- User shown how to top up pressure and operate basic controls.
- Warranty registration explained; service interval advised.
- Inhibitor test result recorded; next service date noted.
Customer advice at handover
- Normal pressure range and when to call for help — pressure guide.
- Do not leave filling loop open.
- Annual service requirement for warranty and safety.
- Signs of poor hot-water performance — hot water problems guide.
Related guides
Pipework layout and system protection: installation best practice. Sizing and datasheet interpretation: reading combi datasheets and sizing & efficiency.
This checklist is a summary for competent Gas Safe registered engineers. Always follow the manufacturer’s installation and commissioning instructions for the specific appliance.