Distinguish pressure conditions and measurement points before diagnosing a supply fault.
A pressure reading needs a location and an operating condition. Record both before interpreting the number.
Standing pressure: no gas flow
Take the reading with the supply available but no gas being drawn. Allow the conditions to settle and compare with the applicable no-flow requirements. The nominal working-pressure figure is not an exact standing-pressure pass mark.
A continuing rise after the setup and stability have been checked can suggest a regulator that is not locking up. The observation prompts investigation; it does not prove a particular component fault without those checks.
Working pressure: the specified demand
Measure while gas is flowing under the load required by the test. A typical domestic natural-gas appliance has a nominal inlet designation of 20 mbar; judge the actual reading against its manufacturer’s limits and specified test point. A satisfactory no-flow reading cannot prove that the supply maintains pressure under demand.
Locate a pressure loss before naming the fault
Compare meter-outlet and appliance-inlet working pressures under the same load. If the meter outlet is satisfactory but the appliance inlet is too low, investigate the path between them, including sizing, restrictions and valve positions. If the meter outlet is also too low, the upstream supply or regulator needs investigation through the appropriate authorised route.
The difference between standing and working readings at one point is not the pressure loss along the installation pipework. For domestic natural gas, that pipework is designed for no more than 1 mbar loss at maximum design demand. Keep this separate from any additional manufacturer-specified loss inside an appliance before its gas-valve test point. LPG has different criteria.
Burner pressure is a separate measurement
Where the appliance instructions require a burner-pressure check or adjustment, use the specified method and setting. Do not assume a modern premix appliance is commissioned by a generic burner-pressure adjustment: follow its combustion and gas-control instructions. Complete the required gas-rate, combustion, flue and other safety checks before handover.
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