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How to use a gas bottle level indicator

Updated: 22 October 2026

You have stuck a card on the cylinder, the bars look full, and the heater still dies before breakfast. How to use a gas bottle level indicator comes down to two different sequences. A magnetic card is a colour boundary on a cooling wall, and you read it only while gas is leaving the bottle. A Truma-class probe is an LED at one height, and you read that light with the head square and clean. Mixing the two instructions is how a working tool gets returned. The products in the [gas bottle level indicator comparison](/hub/measuring-equipment/gas-bottle-level-indicator) do not share one wait time. Nothing was laboratory-tested. If you buy through our amazon.co.uk links, we may earn a commission at no extra cost to you.

You have stuck a card on the cylinder, the bars look full, and the heater still dies before breakfast. How to use a gas bottle level indicator comes down to two different sequences.

Our top picks

Truma Truma LevelCheck

Best overall

Truma Truma LevelCheck
9.2/10about £74.99
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Volnamal Volnamal magnetic strip

Best value

Volnamal Volnamal magnetic strip
6.6/10about £3.99
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OOBRAN OOBRAN magnetic strip

Alternative

OOBRAN OOBRAN magnetic strip
5.3/10about £3.95
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On this page
  1. 1.Put the card on the lower half
  2. 2.Turn the gas on, then wait
  3. 3.Read the colour boundary
  4. 4.If you have a probe

Put the card on the lower half

Start with a wall a magnet will hold. Wipe the lower half so paint flakes, a barcode sticker, and locker dust are not sitting between the card and the steel. Volnamal and OOBRAN both say to clean that lower area. Cowiny and Rivvra add that the cylinder should be steel, and Cowiny tells you to check the magnet before you trust the card. A card on the upper half can stay warm until the liquid has already fallen past it. Berger & Schröter gives an ambient window of about 0 °C to 50 °C and tells you to slide the card if the face stays blank.

Turn the gas on, then wait

Open the cylinder valve, light the appliance you actually use, and leave it drawing gas. A strip measures evaporation cooling. With the appliance off, every bar can look the same. Volnamal's reviews say the regulator needs to be on, not merely fitted. Treat 10 minutes as the Volnamal and OOBRAN instruction, not as a law for every brand. Joyyhaus says about 30 seconds and does not say to turn the gas on. GzGengHe says the reading is instant. Do not average those into the 10-minute cards. If the wall has not cooled, another minute will not draw a line.
Truma Truma LevelCheck

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Truma Truma LevelCheck
9.2/10about £74.99
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Read the colour boundary

Read the change, not the word full printed at the top of the card. Where the colour shifts is the height the wall has cooled to. Above that line the wall is warmer. Below it the liquid is still taking heat out of the steel. If several bars change, Thermographics tells you to use the leftmost of those bars on its sheet. A regulator gauge on the hose stays high while any liquid remains and falls when the liquid has gone. Do not use that needle to decide which bar on the card is half. When the colour step and a planned trip disagree, weigh the cylinder and subtract the tare on the collar disc. The buying guide sets out when the scales are the method you wanted in the first place.

If you have a probe

Keep the probe's sequence away from the card's. Truma's LevelCheck listing tells you to place the meter horizontally on the bottle. The manufacturer page says the head meets the wall at 90 degrees, you do not drag it down the steel, and you repeat the check at several heights. Green at the bottom and red higher up is a level you have found by steps. Truma notes that aluminium transfers dust onto the head, so wipe the tip with a damp cloth. The listing bullets do not require the appliance to be running. One operating description says to shut appliances off before you measure. Follow the sheet with the meter you hold. Do not copy the strip's 10-minute burn onto the probe. The stated bottles are steel and aluminium from 200 mm to 350 mm. A smell that stays is for a Gas Safe engineer qualified for LPG. The locker check is on the caravan and motorhome page. Which sensor answers which question is on magnetic versus ultrasonic.

Common questions

How long do I wait?
Follow the sheet in your packet. In this set, Volnamal, OOBRAN, and Avvchuy say about 10 minutes. Northgas prints 10 minutes as well. Thermographics prints 2–5 minutes for one of its indicators. Joyyhaus says about 30 seconds, and GzGengHe says instant. Those shorter claims are not a correction of the 10-minute cards. If the wall has not cooled, the timer is not the fault.
Which bar is winter and which is summer?
On the Volnamal and OOBRAN instructions, the left bar is the winter bar and the right bar is the summer bar. Read the boundary on the bar that is active, not every block that happens to look dark. If several bars change, a Thermographics sheet says to use the leftmost of them. A hot locker can light bars that are not the liquid line.
Why is there no colour on a full bottle?
The liquid line can sit above a card stuck low on the wall. With no temperature step on the card itself, the face stays blank even though the bottle is full. Slide the card upward until a boundary appears, then return it to the lower half for the next check. An empty bottle can look blank for the opposite reason: nothing left to cool the steel.
What do green and red mean on a Truma?
Green means the meter detects liquid at the height where you are holding the head. Red means it does not detect liquid there, or the contact is poor. Check several heights. A single green light at a random spot is not a percentage and not a full bottle. Clean the tip, hold the head at 90 degrees, and do not drag it along the wall.
Does a warm day make every bar look full?
It can. The cards react to temperature. Sun on one side of a locker, or a warm steel wall with the gas off, can colour the whole strip. Buyer notes describe columns that moved in the sun when they would not move on a cold bottle. Read the card while gas is flowing, and out of direct sun.

Related pages

Best gas bottle level indicator

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Magnetic vs ultrasonic gas bottle level indicator choice

Sources

Public UK sources from the research digest, last checked around 20 October 2026. Shelf prices and star lines are the amazon.co.uk figures captured with these twelve listings. The price bands are this set, not a market average.

  1. Thermographics: gas level indicator theory (retrieved 20 October 2026)
  2. Liquid Gas UK: cylinder guidance for consumers (retrieved 20 October 2026)
  3. HSE: LPG legal framework (retrieved 20 October 2026)
  4. GOV.UK: LPG general information (retrieved 20 October 2026)
  5. Flogas: how to tell if a cylinder is empty (retrieved 20 October 2026)
  6. Truma LevelCheck product page (retrieved 20 October 2026)
  7. Gas Safe Register: frequently asked questions (retrieved 20 October 2026)
  8. Calor: gas bottles and Gas Trac (retrieved 20 October 2026)