Why won't my oil boiler work after a delivery?

The common causes

• Air in the fuel line. If the tank ran dry, air gets into the pipe to the burner. After the refill the burner is likely to fail to start and lock out until the line is bled.
• Sludge or water stirred up. Over time water (from condensation or rain getting in), dirt and even microbial growth settle at the bottom of a tank. UKIFDA, the fuel distributors' association, notes that water in a tank can be stirred up during a delivery, and that keeping at least 12 inches of oil in the tank avoids disturbing sediment that could clog the pipes.
• A blocked filter. That debris can clog the oil filter and pipes between the tank and the burner and starve it of fuel.
• Lockout. Whatever the cause, a burner that fails to light shuts itself down for safety and waits for a reset.

Faulty fuel is rarely to blame. UKIFDA says delivered oil is made to a British Standard, and boiler problems blamed on the fuel almost always trace back to what was already in the household's tank.

Safe checks you can do

These are based on OFTEC's own checklist and need no tools and no work on the boiler itself:

1. Power: is the programmer display lit? If not, check the fuse box for a tripped switch and that the boiler's power switch is on.
2. Controls: a power cut can reset the timer. Set the right time and day, and turn the room thermostat up.
3. Oil: confirm the delivery actually went in. If it is safe to reach, look in through the fill cap or dip the tank, as gauges can fail.
4. Pressure: on a combi or sealed system, a gauge reading under 0.5 bar means the system may need topping up with water; your boiler manual explains how.

Resetting the burner

A lockout is usually shown by a red light or a symbol on the boiler. OFTEC says you can reset a burner, but for safety never more than twice, following the user instructions for your model. A boiler maker's guidance adds that pressing reset repeatedly without fixing the cause can damage the burner. If it locks out again, stop there.

When to call an OFTEC technician

• It still will not fire after two resets.
• It fires, then cuts out again, which can be a sign of water or dirt in the oil.
• The tank ran dry and the line needs bleeding, unless your boiler maker gives owners instructions.
• You smell oil, see oil around the tank, pipes or boiler, or see smoke.

A technician can bleed the line, clean or change the filter and test the tank for water. If they find sludge or water, ask about having it removed (see water in your oil tank and sludge). Never wash spilled oil into a drain; if oil is heading for a drain or watercourse, call the pollution hotline: 0800 80 70 60 in England, Scotland and Northern Ireland, or 0300 065 3000 in Wales.

Stop it happening next time

Both of the main causes are more likely when the tank runs very low. UKIFDA recommends keeping at least 500 litres in the tank where possible and never less than 12 inches, and having the tank checked for water at the annual service. Reorder early (see when to reorder), and compare prices for your postcode before you do.