How to check your
heating oil level

Method 1: Reading a float gauge

Most UK domestic oil tanks are fitted with a float gauge, a clear plastic or glass tube on the side or top of the tank, marked with Full, ¾, ½, ¼, and Empty. A float inside the tank rises and falls with the oil level, and a marker rod or float indicator shows the current level.

Reading it is straightforward: look at where the marker sits against the graduated scale. Bear in mind that these gauges are approximate. They show a rough level, not an exact litre reading. A tank showing "¼" could contain anything from 200 to 400 litres depending on the tank's shape and capacity.

If the float appears stuck (shows the same level regardless of oil use), gently press the float indicator down inside the gauge housing. If it springs back up, the gauge is working. If it stays down or doesn't respond, the float mechanism may be damaged and the gauge needs replacing.

Method 2: Manual dipstick

If your gauge is broken or you want a more accurate reading, a dipstick (or a clean wooden stick, ruler, or broom handle) gives you a direct measurement of the oil depth in the tank.

Steps:

1. Locate the fill point or inspection hatch on top of your tank
2. Remove the cap carefully: avoid sparks or naked flames near the tank
3. Lower the dipstick straight down until it touches the tank floor
4. Remove it and read the oil level from the wetted portion
5. Replace the cap immediately

To convert the depth reading to litres, you need to know your tank's dimensions. Most standard 1,000L rectangular tanks are roughly 1m tall. so 25cm of oil depth is approximately 250 litres. For cylindrical tanks, the conversion is less linear; check your tank's documentation or ask your supplier for a calibration chart.

Method 3: Smart oil monitors

Smart oil monitors are increasingly popular. Devices like the Watchman Sonic or Alert Plus use ultrasonic sensors to measure the distance from the sensor to the oil surface, converting this to a litre reading and transmitting it to an app or a home display unit.

Benefits include: daily level readings without going outside, alerts when the level drops below a threshold, usage tracking over time, and the ability to auto-order or get alerts when delivery is needed. Prices range from £50–£150 for the device, with no ongoing subscription for most models.

For households with tanks in inconvenient locations (underground tanks, tanks in outbuildings far from the house, or tanks without visible gauges), a smart monitor is a worthwhile investment.

Signs you may be running low

• Boiler starting to make unusual noises (air in the fuel line)
• Boiler locking out and requiring a reset more frequently
• Radiators heating unevenly or inconsistently
• Visible sediment or discolouration at the tank's inspection point
• Boiler failing to light at all (the tank may already be empty)

What to do if you run out

If your boiler stops because the tank is empty, you need to:

1. Order an emergency delivery: most suppliers can deliver within 24–48 hours, though this may carry a premium charge
2. Once oil is delivered, do not immediately restart the boiler: allow 30 minutes for sediment disturbed by the low tank to settle
3. Locate the boiler's bleed screw (usually on the pump or filter housing) and bleed any air from the fuel line: most modern boilers have a self-bleeding function, but if yours doesn't, you may need an engineer
4. Press the boiler's reset button and check it fires successfully

If the boiler still won't light after bleeding and resetting, call a qualified OFTEC-registered heating engineer. Don't attempt to dismantle fuel system components unless you're qualified to do so.

How often should you check your level?

During the heating season (October–March), check your tank level at least once a fortnight. In summer, monthly is sufficient. If you have a smart monitor, set an alert at 25% capacity and you won't need to check manually at all.