Running out of oil: what to do before the boiler will restart

Key points on an oil boiler that has run out of fuel

• Air drawn into the line when a tank runs dry does not clear on its own
• A refill alone often is not enough to get the burner firing again
• Sediment from the tank base can clog the fuel filter around empty
• Bleeding the oil line is OFTEC engineer work, not a DIY job
• A tank gauge or audible low-level alarm avoids the problem recurring

What we check first with an oil boiler that has run out of fuel

Diesel-based heating oil is drawn along a single supply line under suction from the burner pump, and once the tank runs dry, air enters that line in place of oil. A refill on its own often is not enough, because the trapped air pocket stops the pump priming correctly and the boiler either fails to ignite or locks out repeatedly on attempted starts. Bleeding the line to purge that air, and in some cases replacing the fuel filter which can pick up sediment stirred up from the bottom of a near-empty tank, are jobs that involve the oil supply line and are OFTEC-registered work, not a homeowner task.

What we see week to week with an oil boiler that has run out of fuel

The off-grid villages around the Mendips and Chew Valley rely on oil almost entirely, and a mid-winter delivery delay running a tank to empty is one of the most common reasons we get an out-of-hours call in that area. Fitting a simple low-level alarm on the tank, checked at each annual service, gives enough warning to book a delivery before the boiler stops rather than after.

Where we deal with this

• Monkton Combe (BA2) · 10 mi
• Clandown (BA3) · 1 mi
• Oakhill (BA3) · 6 mi
• Wookey Hole (BA5) · 11 mi

Questions we get asked

Can I bleed the oil line myself?

No. This involves the oil supply line and safety devices and should only be carried out by an OFTEC-registered technician.

Will the boiler damage itself trying to restart on air?

Repeated failed ignition attempts on an air-locked line put unnecessary strain on the pump and ignition components, so it is worth stopping and booking an engineer rather than restarting it many times over.

How can I avoid this happening again?

A tank contents gauge you check regularly, or a fitted low-level alarm, both give enough notice to arrange a delivery in good time.