Services · Boiler help

Oil boiler not firing? Let's sort it.

No heat, a lockout light, or nothing after a delivery? Answer a couple of quick questions and we'll walk you through it, step by step — safely, and in plain English.

Smell of fumes, or feeling unwell? Carbon monoxide can't be safely diagnosed at home. Get everyone out into fresh air, leave the doors open as you go, and don't go back inside. Call the emergency services (112 or 999) or a registered technician from outside, and don't use the boiler again until it's been checked. A fuel leak? Stop the flow at the tank and call a specialist — never hose it down.

Troubleshoot your oil boiler

What's going on with your heating?

Pick the closest one. We'll walk you through it, step by step.

Reference

Common oil-boiler problems & what to do

Prefer to browse? Tap any problem below to see what to do. When in doubt, stop and call an OFTEC-registered technician — it's the recognised standard for oil-heating work in Ireland.

Quick fixes you can often do yourself

The most common causes of no heat — usually power, the controls, or a run-out.

Quick fixCheck the power first

No lights usually means the boiler isn't getting electricity — an easy thing to rule out.

  • Check the boiler's fused switch (often a spur on the wall nearby) is switched on.
  • Check your fuse board for a tripped switch and flip it back on — once.
  • If it trips again straight away, stop. That's an electrical fault — call an electrician or an OFTEC-registered technician.
  • If the power comes back and stays on, come back and choose "Yes, it has power".
Quick fixGive the controls a chance

A surprising number of "no heat" moments are just the controls.

  • Turn the room thermostat well above the current room temperature.
  • Set the timer/programmer to "on" or "constant".
  • Wait 10–15 minutes — some systems take a little while to fire and warm up.
  • Still nothing after that? Come back and choose "Yes — thermostat is up and timer is on".
Quick fixUsually air or sludge in the system

Banging or kettling (a rumble like a kettle) is rarely an emergency — it's normally trapped air or a build-up in the system.

  • Bleeding your radiators (top valve, with a radiator key) often clears trapped air.
  • If it keeps happening, the system may need a power-flush (a professional sludge clean-out) or the boiler a service.
  • It's worth booking an annual service to keep it efficient — and burning less oil.
Quick fixCheck it's actually asking for heating

Hot water with no heating at all is usually the programmer or a zone valve, not the boiler.

  • Make sure the programmer has HEATING switched on, not just hot water.
  • Turn the room thermostat well up, and give it 10–15 minutes.
  • If both are set and the radiators still stay cold, a motorised/zone valve or the pump may have failed — that's a job for a technician or plumber.
Quick fixTrapped air or balancing

A few cold radiators among warm ones is almost always trapped air or balancing — not a boiler fault.

  • Bleed the cold radiators with a radiator key (top valve) until water, not air, comes out.
  • Check the radiator valves (including any TRVs) are open.
  • If a whole zone stays cold, or it comes back after bleeding, a motorised/zone valve may have failed — that's one for a technician or plumber.

Worth doing carefully

Fine for most people — just follow the one-reset rule, and stop if you're unsure.

Take careReset it — once, and only once

This is the single most important safety rule with an oil boiler.

  • Press and hold the reset / lockout button for a few seconds, then let go.
  • NEVER reset more than once. Each failed reset pumps unburned oil into the combustion chamber — repeated resets are a genuine explosion risk.
  • If it fires up and runs: great. Keep an eye on it for a few minutes.
  • If it locks out again, stop there. Don't reset a second time — call an OFTEC-registered technician.
Take careBleeding the fuel line

With air in the line, the burner usually needs bleeding before it'll light.

  • Plenty of people do this in about five minutes — but it involves the fuel line and the burner, so if you're not confident, stop now and call an OFTEC-registered technician.
  • If you're comfortable: switch the boiler off first, find the bleed point on the fuel pump, and slowly release the air until clean oil (no bubbles) comes through, then close it.
  • Switch back on and reset once (and only once — see the one-reset rule).
  • If it still won't fire, or you're unsure at any step, stop and call a registered technician.
Take careWorth getting looked at

A new, loud hum or vibration is often the pump or fan starting to struggle.

  • It's not usually an emergency, but it's best caught before the part fails completely (and leaves you cold).
  • Book an OFTEC-registered technician for a service / look-over.

Emergencies — stop and get help

Rare, but if one applies to you, don't try to fix it yourself: get to safety and call a professional. Tap any one to see what to do.

EmergencyStop — treat this as a carbon-monoxide risk

Fumes, or feeling dizzy, headachy or drowsy, can mean carbon monoxide. You can't safely diagnose CO yourself.

  • Get everyone out into fresh air now, and leave the doors open as you go.
  • Don't go back in, and don't try to find the source yourself.
  • Call the emergency services (112 or 999) or a registered technician from outside.
  • Don't use the boiler again until a registered technician has checked it.
EmergencyStop the flow and call a specialist

A heating-oil spill is a job for a professional — it can be an environmental and insurance matter, not just a clean-up.

  • If you can do it safely, close the valve at the tank to stop the flow.
  • Don't hose it down, don't cover it, and keep ignition sources away.
  • Call an OFTEC-registered technician — and your home insurer.
  • If oil has reached a drain, a watercourse or a neighbour's property, also tell your local authority.
EmergencyThis one's a technician's job

Power's on, controls are calling for heat, and there's oil — but it still won't fire.

  • Quick safe checks first: make sure the oil line valve at the tank is open, and that the boiler isn't in an "off"/holiday mode.
  • If there's a reset/lockout button, you can try it once (never more — see the one-reset rule).
  • Beyond that, a no-fire usually points to the burner, pump, photocell or nozzle — these aren't DIY parts.
  • Book an OFTEC-registered technician to diagnose it safely.
EmergencyStop resetting it

A boiler that keeps locking out has an underlying fault — and repeated resets are dangerous.

  • Don't press the reset again. Each failed reset floods the chamber with unburned oil — that's a real explosion risk.
  • Repeated lockouts usually mean air, a blockage, or a pump/photocell fault that needs fixing.
  • Leave the boiler switched off and call an OFTEC-registered technician.

Oil boiler questions, answered

Why is my oil boiler not firing — no heat or hot water?
Most no-heat call-outs turn out to be power or controls, not the boiler itself. Check the boiler's fused switch is on and that nothing has tripped on the fuse board, then make sure the thermostat is turned well up and the timer is set to on. If it has power and is being asked for heat but still won't fire, the next thing to check is the oil — a run-out or a fresh delivery draws air into the line, which is the classic reason a boiler won't light.
How do I reset an oil boiler lockout — and how many times can I press it?
Press and hold the reset/lockout button (usually red) once, for a few seconds. Never reset more than once. Each failed reset pumps unburned oil into the combustion chamber, and repeated resets are a genuine explosion risk. If it fires and runs, keep an eye on it. If it locks out again, stop — do not reset a second time — and call an OFTEC-registered technician.
My boiler won't fire after an oil delivery or after running out. What do I do?
After a run-out or a fresh fill, air gets into the fuel line and the burner needs that air cleared before it'll light. If there's a reset button, try it once (and only once). If there's no reset button, the burner usually needs bleeding — many people do this in about five minutes, but it involves the fuel line and burner, so if you're not confident, stop and call an OFTEC-registered technician.
What does it mean to bleed an oil boiler, and is it safe to do myself?
Bleeding clears trapped air from the fuel line so the burner can light again after a run-out. Plenty of people do it themselves: switch the boiler off, find the bleed point on the fuel pump, and slowly release the air until clean, bubble-free oil comes through, then close it and reset once — once only. Never press the reset a second time: each failed reset pushes more unburned oil into the combustion chamber, which is an explosion risk. If you're unsure at any step, stop and call a registered technician — there's no shame in it.
I can smell oil or see a leak near the tank. What should I do?
Treat a heating-oil spill as a job for a professional. If you can do it safely, close the valve at the tank to stop the flow. Don't hose it down or cover it, and keep ignition sources away. Call an OFTEC-registered technician and your home insurer — and if oil has reached a drain, a watercourse or a neighbour's property, tell your local authority too.
I can smell fumes or feel dizzy and unwell. Could it be carbon monoxide?
Possibly — and you can't safely diagnose carbon monoxide yourself. Get everyone out into fresh air straight away, leave doors open as you go, and don't go back in. Call the emergency services (112 or 999) or a registered technician from outside, and don't use the boiler again until it's been checked.

This troubleshooter is general guidance for oil-heated homes in Ireland, not a substitute for a qualified technician. Oil heating involves combustible fuel and a risk of carbon monoxide — if you're ever unsure, stop and call an OFTEC-registered technician.