Knowing how to test gas pressure correctly is essential for safe boiler installation and servicing in the UK. Standing pressure, working pressure and burner pressure checks confirm that the gas supply and appliance controls are within manufacturer tolerance before you sign off the job.
TL;DR: Isolate safely, connect your manometer to the correct test point, zero the instrument, record standing and working pressures in mbar, then compare against the appliance data badge and manufacturer instructions. Use a calibrated digital manometer with clear mbar display for repeatable results.
Before you start: safety and preparation
Only competent persons should carry out gas pressure testing. Gas Safe registered engineers must follow current standards, risk assessments and manufacturer data. Confirm the appliance is suitable for the gas type, inspect hoses and connections, and ensure the workspace is ventilated.
Engineers frequently report that preparation saves callbacks: check battery condition on digital manometers, carry spare hoses, and zero the unit before connecting to the test point. A backlit screen makes a measurable difference in unlit cupboards where analogue dials are hard to read.
Equipment you need
- Calibrated digital manometer or approved test gauge
- Correctly sized hoses and adaptors for the appliance test point
- Manufacturer instructions and data badge reference values
- Means to record readings for job sheets or certificates
The Manompress mini digital manometer is designed for low-pressure gas and HVAC diagnostics: dual-port differential measurement, -101 to 200 kPa range, ±0.3% FSO accuracy, mbar display, data hold, zeroing and a backlit LCD. It includes silicone hoses for typical diagnostic ports.
Step-by-step: how to test gas pressure on a boiler
Step 1 — Zero the manometer
Power on the instrument with no pressure applied. With hoses disconnected from test ports, press zero until the display reads 0.00. This removes offset drift and is a step many field discussions flag as easy to skip under time pressure.
Step 2 — Measure standing pressure
With the appliance off and gas available at the meter, connect to the designated test point (often at the meter or upstream test nipple). Record standing pressure and compare with the allowable supply range for the installation. Note the value in mbar on your worksheet.
Step 3 — Measure working (operating) pressure
Light all relevant appliances on the installation to simulate maximum demand where required by the test procedure. Record working pressure at the appliance test point. It should remain within manufacturer limits while other appliances are running.
Step 4 — Check burner pressure
At the appliance burner pressure test point, record the value at the specified firing rate. Compare directly with the data badge and manufacturer chart. Out-of-range burner pressure can indicate regulator, gas valve or inlet supply issues.
Step 5 — Differential checks across the gas valve (if required)
Some procedures require comparing pressure upstream and downstream of the gas valve. A dual-port digital manometer displays the differential directly, reducing manual calculation errors. See our differential pressure guide for background on ΔP testing.
Step 6 — Record and reinstate
Document all readings, disconnect hoses safely, replace test point seals if disturbed, and confirm the appliance operates correctly before leaving site.
Common mistakes to avoid
- Testing without zeroing the manometer first
- Using an instrument with unsuitable pressure range or poor mbar resolution
- Reading an analogue dial at an angle in poor light
- Mixing up standing, working and burner pressure reference values
- Failing to account for other appliances on the same supply during working pressure tests
When to call for further investigation
Pressure outside manufacturer tolerance, unstable readings, or significant drop when additional appliances operate may indicate undersized supply, regulator faults, pipework restrictions or gas valve problems. Do not adjust components beyond your qualification scope; escalate according to Gas Safe requirements and company policy.
Frequently Asked Questions
What units should I record for UK gas pressure tests?
Millibars (mbar) are standard for domestic gas work in the UK. Ensure your manometer displays mbar clearly and that you record the same units on certificates.
Can I use one manometer for tightness testing and pressure testing?
Different procedures may require specific instrument classes and configurations. Always use equipment appropriate to the test being carried out and verify it is within calibration date.
How often should my manometer be calibrated?
Follow manufacturer guidance and your company quality system. Instruments used for compliance records should be verified on a defined schedule against traceable standards.