Guides to the tanks we install and inspect across Norfolk – plastic and steel, single-skin and bunded – covering how each type fails, which fittings cause trouble, and what an inspection actually looks at.
Why tanks get their own section
A boiler that fails stops working. A tank that fails puts fuel into the ground, and in drained Norfolk the ground connects to a ditch, and a ditch connects to a watercourse. The clean-up liability sits with the property owner and it dwarfs the cost of the tank.
It is also the component most people never look at. Most householders last examined their oil tank on the day it was installed, and the failure modes give years of warning to anybody who is watching.
The two materials, and how each fails
| Plastic (polyethylene) | Steel | |
|---|---|---|
| Fails by | UV degradation and mechanical stress | Corrosion, from the inside out |
| Visible warning | Crazing, bulging, deformation, weeping at seams | Rust weeping through seams and near the base |
| Worst enemy | Sunlight, and an uneven base | Water settling inside under the oil |
| Where it fails | Usually low down on the sun-facing side | Usually the base or a low seam |
| Fire resistance | Poor | Good |
| Weight | Light | Heavy |
| Typical life | Fifteen to twenty-five years, position-dependent | Similar, and more sensitive to water ingress |
The key insight about steel tanks is direction: they corrode from the inside out, driven by water settling under the oil. By the time rust weeps through to the outside, the metal at that point is already thin. Full detail in plastic vs steel oil tanks.
The fittings that cause trouble
- Sight gauges perish and go brittle. A failed sight tube empties the tank onto the ground, and it usually does it when nobody is there. It is a cheap part and it should be replaced at the first sign of clouding or brittleness.
- Vent caps go missing, letting rain straight into the tank. This is where most water-in-fuel problems originate.
- Fill caps go missing too, which is both a contamination route and an invitation – heating oil gets stolen.
- Outlet valves seize, which means you cannot isolate the tank in an emergency.
- Filter bowls crack, and the filter element itself is a consumable that should be changed at every service.
- Float gauges stick, reading wrong without obviously failing – which is how people run dry.
- Fire valve sensors fall out of position or were never correctly sited, meaning the valve would not do its job in a fire – see oil supply pipework and fire valves.
Bunded and single-skin
Whether your installation requires secondary containment is determined by a risk assessment, not by preference. In this county the watercourse condition catches a great many properties – Norfolk is drained land and field ditches count, including ones that are dry for much of the year.
A bund is only containment while it is empty and intact:
- Rainwater fills an open-top bund, reducing its capacity and, on a steel tank, sitting against the tank accelerating corrosion.
- Drain plugs left out turn a bund into a decorative outer shell.
- A cracked outer skin on a plastic bunded tank means no containment at all.
- The gap between the skins is where a slow inner-tank leak shows up first, and it is the most useful thing to inspect.
What an inspection covers
More than a look at the tank:
- The tank – material, condition, crazing, corrosion, deformation, seams.
- Secondary containment – required or not, present or not, intact or not.
- The base – level, condition, extent, drainage. The most common underlying cause of tank failure.
- Siting and separation – measured distances to the building, openings, eaves, boundaries and combustible screening.
- Environmental risk – distance to watercourses, ditches, drains and any water supply source.
- Fittings – fill point, cap, vent, gauge, outlet valve, filter.
- The oil line – material, protection, joints, flexible sections, and the fire valve and its sensor position.
It produces a written report with photographs, separating what needs doing now from what to plan for. See oil tank inspection.
Each model page below is populated from what we actually find on the job – common faults, part numbers, service quirks and access notes – rather than from manufacturer literature. That takes time to accumulate and it is worth more than a rewritten brochure. Pages appear as the records support them.
Tank over fifteen years old? Ten minutes with a torch in the spring tells you most of what you need to know.
Questions we get asked about this
How long does an oil tank last?
Roughly fifteen to twenty-five years, and position matters far more than age. A plastic tank in full sun on a poor base will not reach the lower end; a steel tank kept dry can beat the upper end.
Does my tank need to be bunded?
It depends on the risk assessment for your site. In Norfolk the proximity-to-watercourse condition catches a great many properties, because field ditches count – including ones that are dry for most of the year.
Can a leaking tank be repaired?
No. A containment vessel cannot be patched. The fittings can be replaced; the tank cannot.
What is the most common cause of tank failure?
The base. An inadequate or settled base stresses a plastic tank continuously and lets water sit under a steel one. It is the single most consequential thing to get right.
Should I worry about water in the filter bowl?
Yes – it tells you there is water in the tank. On steel that water is actively corroding the floor, and on any tank it will eventually reach the burner and cause lockouts.
Is my tank at risk of theft?
Heating oil is stolen, particularly from rural properties visible from a road. A lockable fill cap and an electronic gauge with a drop alarm are inexpensive precautions.
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Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.