How do I look after a heating oil tank in winter?

Around 1.5 million UK homes are heated by oil, mostly off the gas grid, and the failures cluster in December and January. Water accumulates in the tank through condensation and through a poorly sealed lid, and in freezing weather it turns to ice in the line or feeds the bacteria that make sludge. Kerosene itself does not freeze at UK temperatures, but the filter can wax and block, and the tank bottom is where every problem lives.

Safety

What you'll need

• A dipstick or a working tank gauge
• Spare filter elements for the tank and the boiler
• A water-finding paste or a clear sample jar (optional)
• Absorbent granules or a spill kit
• The number of your oil supplier and an OFTEC engineer

Step by step

1. Walk round the tank in autumn and look at it properly.Plastic tanks: look for crazing, bulging, splits and discoloured patches, especially on the sunny side. Steel tanks: look for rust at the base, at the weld seams and around the outlet. Both: check the legs, base and supports are sound and level.
2. Check for oil staining or a smell anywhere around the base.Dark staining on the base, dead vegetation, or a persistent oil smell means a leak. That is an OFTEC engineer's job and possibly a pollution report, not something to patch.
3. Empty and check the bund.A bunded tank has an outer skin to catch a leak. It only works if it is empty — standing rainwater in it means a leak has nowhere to go and the water needs pumping out and disposing of properly, not tipping on the garden.
4. Check for water in the tank.Water-finding paste on a dipstick changes colour where water sits at the bottom. Any significant depth needs draining out by the supplier or an engineer — water is what causes sludge, blocked filters and winter failures.
5. Change the filters before the season, not during it.There is usually one at the tank and one at the boiler. They are inexpensive, and a blocked filter on the coldest night of the year is the single most common oil boiler failure.
6. Check the lid, the vent and the gauge.A cracked or missing lid lets rain straight in. A blocked vent stops the tank breathing and causes delivery problems. A stuck gauge is why people run out.
7. Keep the fuel line protected and the valve accessible.The supply line should be protected where it runs above ground, and there should be a fire valve at the boiler. Know where the tank's isolation valve is and keep it clear and free to turn.
8. Clear vegetation and standing water from around the tank.Ivy and shrubs against a plastic tank retain moisture and hide damage; a tank sitting in a puddle rusts at the base. A clear metre all round, on a sound level base, is the standard.
9. Order before you drop below a quarter of a tank.Deliveries take longer in cold weather and at Christmas, and the last quarter is where the sludge and water are. Ordering at a quarter full costs the same and removes the risk.
10. Have the boiler serviced annually by an OFTEC registered engineer.Oil boilers need it more than gas ones — the nozzle, the electrodes and the combustion settings all drift. It also keeps the warranty and satisfies most insurers.

Tips

• Join or start a local oil buying group. Bulk orders are cheaper per litre and are usually prioritised for delivery, which matters most in exactly the weather when everyone else is ordering.
• Fit a remote tank gauge or a telemetry monitor if the tank is out of sight. Most running-out incidents are simply nobody having looked.
• Oil theft is common in rural areas. A lockable fill cap, a tank alarm and screening from the road all help, and insurers sometimes require a lock.
• A plastic tank has a life of roughly 20 years and a steel one somewhat less if it is unprotected. Both should be replaced rather than repaired once they show structural damage.
• Keep absorbent granules or a spill kit near the tank. A small spill dealt with in five minutes is a domestic clean-up; the same spill an hour later is a contamination problem.

Common mistakes

• Running the tank low to make it last until payday — The bottom of the tank is where water and sludge sit, and drawing it through blocks filters and stops the boiler. It also means an emergency delivery at a premium and a possible lock-out.
• Hosing a spill away — It carries oil into a drain and then into a watercourse, which turns a contained spill into a reportable pollution incident with potential enforcement. Contain it with granules or sand and ring the incident hotline.
• Leaving rainwater sitting in the bund — A full bund cannot catch a leak, which is its entire purpose. It has to be pumped out and the water disposed of properly, not tipped onto the ground.
• Repairing a cracked plastic tank — Nothing bonds reliably to weathered polyethylene, and a failed repair releases the whole contents. A damaged plastic tank is replaced.

If it doesn't work

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