Guide · 2026-10-06
Working pressure at the gas meter: 18.5 to 23 mbar, and the 1 mbar rule
On a domestic natural gas supply the meter outlet should read between 18.5 and 23 mbar after one minute at load, and you should lose no more than 1 mbar between the meter and the appliance. Here's where those numbers come from and how to take the readings so they mean something.
Straight to the questions →The numbers
| What | Figure | Where it comes from |
|---|---|---|
| Meter outlet working pressure, natural gas | 18.5 to 23 mbar | IGEM/G/13 (2022, amended 2023) |
| Nominal supply pressure | 21 mbar | Gas Safe TB 129 |
| Drop, meter outlet to appliance inlet, natural gas | 1 mbar max | BS 6891, via Gas Safe TB 129; IGEM/G/13 |
| Propane regulator set pressure | 37 mbar nominal | Liquid Gas UK; Gas Safe TB 129 gives 32 to 45 mbar |
You'll still hear 19 to 23 mbar, or 21 ± 2. That's the older figure, and it's what TB 129 and the BS 6400-1 commissioning range give. IGEM/G/13 is the newer, specific procedure for checking the supply at the meter, and it takes the bottom of the range down to 18.5.
Standing, working and operating pressure
Standing pressure is the reading with no gas flowing. It tells you there's gas and roughly what the regulator is doing, and not much more. There's no published limit for standing pressure on natural gas, so don't call a supply good or bad on it.
Working pressure and operating pressure are the same thing: the reading with gas flowing. IGEM/G/13 says operating pressure, most engineers say working pressure. This is the reading that gets judged against 18.5 to 23 mbar.
A supply that stands at 21 mbar and drops to 17 the moment the combi fires has a problem the standing reading would never have shown you.
Taking the reading at the meter
- Fit a zeroed manometer to the test point on the meter outlet.
- Put the installation under what IGEM/G/13 calls high operating load. In plain terms: the biggest appliance at full rate (on a combi, the hot water at full flow), with the others running at around half.
- Let it settle for one minute, then read it.
- Between 18.5 and 23 mbar is in range. Outside that, it gets reported (see below).
Then take the working pressure at the appliance with the same load on. The difference between the two readings is the drop across the pipework.
The 1 mbar rule
Between the meter outlet and the appliance inlet you're allowed to lose no more than 1 mbar on natural gas. LPG has its own allowance, which TB 129 sets out. More than that and the pipe is undersized for the load, or something in the run is restricting it.
Take the reading at the appliance inlet, not at the gas valve. TB 129 points out that you can lose another 0.5 to 2.5 mbar between the appliance isolation valve and the gas valve test point, depending on the appliance. The manufacturer's instructions say what to expect for that boiler.
When the reading is out
Below 18.5 or above 23 mbar at the meter, report it to the National Gas Emergency Service on 0800 111 999 (Northern Ireland: 0800 002 001). That's the procedure in IGEM/G/13, for high readings as well as low ones. The meter regulator isn't yours to adjust.
If the meter's in range but you're losing more than 1 mbar to the appliance, that's the installation, and it's yours to sort: pipe size, length, fittings, a part-closed valve.
Then gas rate it
A good working pressure doesn't prove the appliance is burning what it should. Pressure first, then a gas rate against the data badge, then combustion. The gas rate calculator below does the arithmetic from a timed meter reading.
Sources
- IGEM/G/13, Communication 1868 (September 2022), reissued with amendments August 2023. Free to download from IGEM; not reproduced here.
- Gas Safe Register Technical Bulletin 129, Boiler inlet gas pressure measurement, 6 October 2020.
- BS 6891:2015+A1:2019, low pressure gas installation pipework.
- Liquid Gas UK, Consumer Guidance Sheet 39 (August 2020).
The app
The inlet pressure for the boiler in front of you
Flint has the inlet and burner pressures, CO₂ figures and gas valve settings from the manufacturer's manual for each boiler, with the page they came from. Plus the gas rate and tightness test tools.
Start 7 days freeThen £3.99 a month or £29.99 a year. Cancel any time.
FAQ
The questions engineers keep asking
What should the working pressure be at a domestic gas meter?
Between 18.5 mbar and 23 mbar at the meter outlet test point, read after a one-minute stabilisation period with the installation at high operating load. That range comes from IGEM/G/13. The nominal supply pressure is 21 mbar.
What is the difference between standing pressure and working pressure?
Standing pressure is the reading with no gas flowing. Working (operating) pressure is the reading with appliances running, and it's the one judged against 18.5 to 23 mbar. There's no published limit for standing pressure on natural gas, so treat it as a guide only.
How much pressure drop is allowed between the gas meter and the boiler?
No more than 1 mbar on natural gas between the meter outlet and the appliance inlet. Gas Safe Technical Bulletin 129 gives that figure from BS 6891, and IGEM/G/13 states the same. LPG has its own allowance, set out in TB 129.
What do I do if the working pressure at the meter is below 18.5 mbar?
Report it to the National Gas Emergency Service on 0800 111 999 (0800 002 001 in Northern Ireland). IGEM/G/13 applies the same to a reading above 23 mbar. The procedure is to report it, not to adjust the meter regulator.
What is the gas pressure for LPG?
Propane regulators are normally set to 37 mbar. Gas Safe Technical Bulletin 129 puts the LPG regulator outlet typically between 32 mbar and 45 mbar. Butane is lower, around 28 to 30 mbar.
Flint is a reference tool for competent, Gas Safe registered engineers. Everything here informs your judgement and never replaces it. Always work to the manufacturer's instructions and the current standards, and check every figure against the appliance data badge and manual.