How to read your gas meter and check for leaks at home

Most people in London never look at their gas meter unless the bill is wrong. Knowing how to read it, and how to do a basic leak test, takes 10 minutes to learn and could save your life. Here is the practical version.

Where your gas meter is

In London houses, the meter is usually:

• In a small cabinet outside the front of the property (most common in modern installs)
• Under the stairs
• In a kitchen cupboard
• In a basement or cellar (Victorian houses)

Inside the cabinet you will see the meter itself (a box with a digital or mechanical display) and the gas emergency control valve (ECV), which is the lever or handle that turns the gas supply off.

If you cannot find your meter, your gas bill will tell you the meter serial number and your supplier can confirm the location.

How to read the meter

Mechanical (mechanical dials or rolling numbers)

Most older meters. The display shows numbers in cubic metres (m³). Some very old meters still show cubic feet (ft³).

To read: write down the digits before the decimal point, ignoring any red digits.

Smart meter

A digital screen showing kWh used. Press the button to cycle through different displays (current usage, total usage, etc.).

The reading you give to your supplier is the cubic metres or kWh number, not the running total of cost.

How much gas you actually use

A typical London household uses 9,000 to 14,000 kWh of gas per year for heating and hot water. That is about 800 to 1,300 m³ on a metric meter.

Daily usage in winter (January peak): 50 to 90 kWh per day. Daily usage in summer: 5 to 15 kWh per day (just hot water).

If your daily usage suddenly jumps without explanation, that is worth investigating. Could be an external leak, could be an inefficient boiler, could be the heating thermostat being set higher than intended.

The 30-second leak test

If you suspect a gas leak, do this:

1. Turn off every gas appliance. Boiler, hob, oven, gas fire if you have one.
2. Watch the meter. On a mechanical meter, the smallest dial (often half-cubic-metre) should not move. On a smart meter, the kWh reading should not increase.
3. Wait 60 seconds.

If the meter is moving with all appliances off, you have a leak somewhere in the gas pipework downstream of the meter. Call the National Gas Emergency Service immediately on 0800 111 999.

This test is not perfect (very small leaks may not register on the meter dial) but it catches significant leaks reliably.

Signs of a gas leak

The five things that indicate gas leak (any one is enough to act on):

1. Smell of gas. Mercaptan, the additive that makes gas smell, is intentionally pungent. If you smell rotten eggs or sulphur near a gas appliance or pipe, gas is escaping.

2. Hissing or whistling sound from a gas pipe or appliance.

3. Black soot or scorch marks around an appliance.

4. Brown or yellow flames at the hob (should be blue) or the boiler (should be blue).

5. Symptoms of carbon monoxide exposure in the household: headaches, dizziness, nausea, especially when at home and improving when you leave.

For symptoms 1, 2, and 5, the response is:

1. Open all windows and doors immediately.
2. Do not turn any electrical switches on or off (they can spark and ignite leaked gas).
3. Do not light matches, lighters, or smoke.
4. Turn off the gas at the meter if you can do so safely (turn the ECV handle 90 degrees so it is across the pipe).
5. Leave the house and call 0800 111 999 (National Gas Emergency Service) from outside.
6. Do not return until the gas engineer says it is safe.

National Grid attends gas emergencies 24/7 and will arrive within 1 hour for a confirmed leak. The visit is free regardless of where the leak is. They will isolate the leak and tell you what needs to be repaired.

Carbon monoxide

Carbon monoxide (CO) is colourless, odourless, and deadly. It is produced when gas burns incompletely (poorly maintained boiler, blocked flue, faulty hob).

Symptoms (in order of severity):

• Headaches when at home, gone when out
• Dizziness or unexplained tiredness
• Nausea
• Confusion
• Loss of consciousness

If anyone in the household has these symptoms and they improve when leaving the house, treat it as carbon monoxide until proven otherwise.

What to do:

1. Get everyone out of the house, including pets.
2. Open windows and doors.
3. Call 999 if anyone has serious symptoms.
4. Call National Gas on 0800 111 999.
5. Do not return until the gas appliance has been inspected.

CO alarms — install them now

Every home with a gas appliance should have at least one CO alarm. UK regulations require landlords to install one in every room with a gas appliance (since 2022). For owner-occupiers it is not legally required, but the cost is small (£15 to £30 per alarm) and the benefit is unmissable.

Where to install:

• One in the same room as the boiler
• One in the same room as the gas hob (if the kitchen is enclosed)
• One in the bedrooms (in case of leaks at night)

Position high on a wall or on the ceiling, at least 1 metre from the gas appliance (so it does not false-alarm from minor combustion gases).

Test alarms monthly. Replace every 5 to 10 years (alarms have a fixed lifespan, written on the unit).

When the gas inspector visits

If you have called National Gas for a suspected leak, the engineer attending will:

1. Use a gas detector to confirm a leak and locate it
2. Isolate the gas at the meter or upstream of the leak
3. Issue a defect notice if needed (specifying what work is required and what is unsafe to use)
4. Leave gas on if the leak is in a single appliance that can be isolated
5. Leave gas off if the leak is in the main pipework

National Grid does not do the actual repair. That is the property owner's responsibility. You will need a Gas Safe registered engineer to:

• Trace and repair the pipework leak, or
• Repair or replace the leaking appliance, or
• Pressure-test the system after any repair

Once repaired, National Grid will return to verify the system is gas-tight and re-energise the supply.

What I do on a gas safety call

If you call me about a suspected gas issue (and the leak is not active, in which case call National Grid first), my standard process:

1. Visual inspection of all visible gas pipework
2. Soundness test (pressurise the gas system and check for any drop over a set period)
3. Inspection of every gas appliance
4. Combustion analysis on the boiler and any gas hob
5. Verification that all flues are clear and venting properly
6. Written report

This is a standard "gas inspection" or part of an annual boiler service. Cost: £100 to £180 depending on whether it is combined with other work.

Knowing where your meter shut-off is

Two minutes today, when there is no emergency. Find your gas meter. Find the ECV (the handle or lever at the meter). Confirm you know which way to turn it (90 degrees across the pipe = off).

If anyone in your household ever needs to shut the gas off in an emergency, the time saved can matter. Worth showing other adults in the house too.

Send me a WhatsApp if you would like a gas safety inspection or you have a specific concern. I cover every London borough and respond to gas-related queries the same day.