Oil boiler not firing: the checks before an OFTEC callout
An oil boiler that refuses to fire is working through a longer chain of mechanical steps than a gas equivalent, which means there are more places for the sequence to stall. Most causes fall into a handful of well-understood categories.
What is actually going on with an oil boiler that will not fire
Fuel supply issues sit at one end of the chain: an empty or near-empty tank, a closed fire valve, a blocked line filter, or waxing of the oil in very cold weather can all starve the burner before it even attempts ignition. At the ignition end, worn electrodes, a fouled nozzle spraying an uneven pattern, or a failed photocell that cannot confirm a flame once lit will all stop the burner completing its cycle and typically trip it to lockout. Because these components sit within the burner assembly and involve the oil supply, diagnosis and any parts replacement is OFTEC-registered work; a homeowner's role is limited to checking the tank level, the fire valve position, and that the boiler has power and is calling for heat.
An oil boiler that will not fire — the facts that change the job
- Check tank level, the fire valve, and boiler power before calling out
- Waxing in very cold weather can restrict oil flow through the filter
- A fouled nozzle sprays an uneven pattern and disrupts ignition
- A failed photocell cannot confirm a flame even when one is present
- Burner and nozzle work sits inside OFTEC-registered servicing
Where we deal with this
Scope of work
- Domestic boiler installation
- Boiler servicing
- Boiler maintenance and repair
Book a visit for an oil boiler that will not fire
The honest position: Check the simple things first: tank, fire valve, power. Everything past that is inside the burner and needs an OFTEC-registered visit.
For gas work, use a Gas Safe registered engineer; for oil work, use an OFTEC-registered technician.
Related help pages
- Oil supply guideRunning out of oil: what to do before the boiler will restart
- Worcester fault codeWorcester A7: sealed system pressure fault on a Greenstar
- Oil odour diagnosisSmell of oil near the boiler: leak, spillage or normal residue
- Hot water diagnosisHot water temperature fluctuating: why taps run hot then cold
- Property typeBoilers in kitchen cupboards: ventilation and worktop clearance
- Off-grid lettingsOil-heated rented homes: what landlords should know
Services that cover this
Questions we get asked
- What is oil waxing and does it affect homes here?
- In prolonged sub-zero conditions, heating oil can partially solidify (wax) and restrict flow through filters and lines. It is more of a risk for exposed outdoor pipework on rural and off-grid properties around the Mendips than for tanks in sheltered positions.
- Can I clean the nozzle myself?
- No. The nozzle and electrodes sit inside the burner assembly and require correct recommissioning and combustion checks afterwards, which is OFTEC engineer work.
- How often should the nozzle be replaced?
- As a wear item, it is typically replaced at each annual service rather than waiting for a failure.
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