The photocell is a safety component that checks whether the burner has established a flame. If it cannot see a clean flame, the boiler may lock out.

Key points

  • Photocell symptoms often look like random lockouts.
  • The photocell may be dirty, failed or reacting to another burner problem.
  • Poor combustion can look like a photocell fault.
  • Testing matters before replacing parts.

What a photocell does

Inside an oil burner, the photocell monitors light from the flame. If the flame is missing, weak or obscured, the burner control box shuts the boiler down.

That shutdown is a safety response. It should not be defeated or worked around.

Common signs

A photocell-related fault may show as the boiler firing briefly and then locking out, intermittent lockouts, or failure to recognise a flame even when oil and power are present.

Soot, dirt, poor flame shape or incorrect burner setup can stop the photocell seeing what it needs to see.

Why it is not always just the photocell

A dirty photocell can be cleaned, and a failed photocell can be replaced, but the engineer still needs to ask why the fault happened.

If the true cause is poor combustion, a blocked nozzle, ignition trouble or an oil supply fault, simply changing the photocell may not fix the problem for long.

How the fault is checked

A proper diagnosis checks the burner sequence, flame quality, photocell condition, wiring, oil supply and combustion readings where the boiler can run safely.

The aim is to prove the fault, not guess at it.

Common questions

Can I clean the photocell myself?

It is better to avoid removing burner parts unless you are competent to do so. A dirty photocell can also be a symptom of poor combustion.

Will replacing the photocell fix lockouts?

Sometimes, but not always. Lockouts can be caused by several burner or oil supply problems.