Press reset once, maybe twice, then stop. What happens during those attempts – fan only, spark but no light, lights then drops out – identifies the fault more reliably than anything else. Most causes are fuel supply, flame proving or ignition.
Before you call: the free checks
- Is there oil in the tank? Gauges stick and lie. Check physically if the tank allows it. Running dry is the single most common cause and it has consequences beyond the restart – see running out of oil.
- Is the fire valve still open? A thermal cut-off in the oil line, which can trip from a hot summer or a knock. If it has tripped, no fuel reaches the burner and every reset will fail.
- Is the tank valve open? Worth ruling out, particularly after any work on the tank.
- Has the electricity been interrupted? Fused spur, RCD, and any isolator switch near the boiler.
- Is the thermostat actually calling for heat? Flat batteries in a wireless room stat present exactly like a dead boiler.
- Is the condensate pipe frozen? In cold weather on a condensing boiler, this shuts it down and it is fixable in ten minutes – see frozen condensate pipes.
Every failed attempt sprays another dose of kerosene into a combustion chamber that did not ignite the last one. Do it repeatedly and you get unburnt oil pooling in the chamber, which at best makes a serious mess and at worst ignites all at once when the boiler finally does light. The damage from repeated resets is entirely self-inflicted.
What the failure pattern tells us
This is the single most useful thing you can describe on the phone. Stand where you can hear the burner and note what happens when you press reset.
| What happens | What it points at |
|---|---|
| Fan runs, no ignition attempt, immediate lockout | No fuel reaching the nozzle – empty tank, closed valve, tripped fire valve, blocked filter, or air in the line |
| Fan runs, you hear the spark, nothing lights | Fuel supply, a blocked nozzle, or ignition not reaching the fuel |
| Lights briefly, locks out after a few seconds | Flame proving – a dirty or failing photocell, almost always |
| Lights, runs for minutes, then locks out | Flame loss during the run – air in the line, a failing pump, or a partly blocked filter |
| Locks out only in cold weather | Frozen condensate, or waxing in an exposed fuel line |
| Intermittent, clears after bleeding | Air being drawn in at a joint or a filter seal |
| No lockout light, nothing at all | Electrical supply, a control fault, or the boiler is not being called |
The intermittent ones are where money gets wasted. They frequently get resolved by replacing the control box, which is the wrong part, and the fault returns weeks later. Air in the fuel line is the usual culprit and it is a much cheaper fix.
What we actually find
- Photocell dirty or failing. The sensor that proves the flame. A film of soot on it means the burner lights and then locks out because it cannot see its own flame. Cheap, and extremely common.
- Blocked or worn nozzle. The orifice is measured in thousandths of an inch and blocks readily, particularly after a run-dry.
- Blocked filters. Tank-side and burner. Both, usually.
- Air in the oil line, drawn in at a weeping joint, a filter seal or a high point in the run.
- Pump not holding pressure, which is a routine replacement on higher-hours appliances.
- Electrode gap or position wrong, giving unreliable ignition.
- Water in the fuel, which will not burn. That is a tank problem presenting as a boiler fault.
- Control box failure, which is a real fault and is diagnosed far more often than it occurs.
Most of those are components we carry. The ones that are not – a specific control box for an obscure appliance – we will tell you about on the day rather than a week later.
What happens when we come out
- We ask you to describe the patternOn the phone, before setting off. It frequently identifies the fault and occasionally resolves it without a visit.
- Fuel firstTank level, valves, fire valve, filters, and whether there is water in the filter bowl. Most no-fire faults are fuel faults.
- Then the burnerOff the boiler and onto a sheet. Nozzle, electrodes, photocell, pump pressure on a gauge.
- Then the chamberIf repeated resets have put unburnt oil in it, that comes out before anything is fired.
- Recommission properlyPump pressure to the data plate, combustion analysed with a calibrated analyser, and you get the readings.
- Tell you why it happenedBecause a boiler that locked out once for a reason nobody identified will lock out again.
If it keeps happening
A boiler that locks out every few weeks is not a boiler that needs resetting more efficiently. Recurring lockouts have a cause and it is worth finding:
- Air ingress on the oil line, which is the commonest and cheapest.
- A tank shedding sludge, typically for weeks after a run-dry, or from a tank nearing the end of its life – see eight signs an oil tank is near the end of its life.
- Water in the tank, from a missing vent cap or a failing steel tank.
- A marginal photocell that works when clean and fails when warm.
- A condensate route that freezes every cold snap.
- A boiler that has not been serviced, drifting further out of tune each year.
There is a fuller explanation of the lockout sequence and what the control box is doing in oil boiler lockouts.
Locked out twice? Stop pressing and call. What the burner does during those two attempts usually identifies the cause before we arrive.
Questions we get asked about this
How many times can I press reset?
Twice. Each attempt puts more unburnt fuel into a chamber that did not ignite the last lot, and the damage from repeated resets is entirely avoidable.
The boiler hums but does not light. What is that?
Usually the fan and pump running with no fuel arriving, or fuel arriving and not igniting. Check the tank, the tank valve and the fire valve first – between them they account for most of these.
It lights and then cuts out after a few seconds.
That is flame proving failing – the burner lights but the photocell cannot see it. A dirty or failing photocell is the usual cause and it is an inexpensive part.
It only happens when it is cold.
Most likely a frozen condensate pipe on a condensing appliance. Check the external plastic pipe before assuming anything else.
Is a lockout dangerous?
No – it is the safety system doing exactly its job by refusing to keep pumping fuel into an appliance that did not prove a flame. What is unwise is defeating it by resetting repeatedly.
There is a smell of oil after several resets.
That is unburnt fuel in the combustion chamber. Stop, ventilate, and do not reset again. It needs cleaning out before the boiler is fired.
What happens when you call
Call and describe it
You speak to an engineer, not a call centre. Most jobs can be narrowed down on the phone.
We look at it properly
A real diagnosis before a price, and a straight answer if it is not worth doing.
A written quote
Itemised, so you can see what you are paying for.
The job, and the paperwork
Certificates where the work needs them, and what will need attention next.
Where we do this work
Across Norwich and the whole of Norfolk. If you are on the edge of the county, call and ask — we will tell you honestly whether we are the right people.
- Norwich
- Wymondham
- Dereham
- Attleborough
- Aylsham
- North Walsham
- Cromer
- Diss
- Loddon
- Long Stratton
- Watton
- King's Lynn
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.