Worcester Bosch Oil Boiler Not Firing Up? Causes & Remedies

Ask an oil engineer why a Worcester Bosch oil boiler is not firing up and the first question is rarely about the boiler. It is about the tank. Worcester Bosch’s own guidance puts running out of oil, a leaking pipeline and contaminated oil at the top of its list of lockout causes, and that matches what we see on call-outs.

At Hinckley Plumbing & Heating we repair Worcester Bosch oil boilers, including the Greenstar Danesmoor, for homes around Leicester, Coventry, Rugby and Loughborough as well as Hinckley, Nuneaton and Tamworth. This guide starts with the likeliest culprits, then works through every other fault we know of, from the tank towards the flame.

What A Lockout Tells You When A Worcester Bosch Oil Boiler Is Not Firing Up

A lockout is the burner’s way of saying it tried to light, did not get a flame, and stopped. It tells you the burner is not working, but not why. The reason falls into one of three groups: the oil is not arriving in good condition, the burner cannot turn it into a flame, or a control or safety device is stopping it.

The Likeliest Culprits, In Order

If your Worcester has stopped firing, the usual suspects are an empty or very low tank, a power or controls problem, air in the oil line, a blocked filter or nozzle, and dirty or contaminated oil. Checking those first solves the majority of cases. The rest of this page covers everything else.

Oil Supply Faults: Why The Burner Is Starved

• The tank has run dry. Easy to miss if the gauge is hard to read. After a delivery, air in the line often needs bleeding out before the burner will prime.
• The oil is contaminated. Water can find its way into a tank through a missing cover or damaged tank, sludge builds up where water meets oil, and an older steel tank may add rust. The remedy is a tank clean and a flush of the oil lines.
• The pipeline is leaking. Air is drawn in and oil seeps out, so the supply never settles. An oil smell or a damp patch near the pipes is a giveaway, and the pipe needs repairing before the line is bled.
• There is air in the line. Even without a leak, a low tank or loose joint lets air in. The pump cannot prime until the line is bled.
• The filter is blocked. Dirt from the tank ends up here, since it is designed to catch it. A new filter at a service often brings the burner back to life.
• The nozzle is blocked or worn. The nozzle’s tiny outlet clogs easily. When it does, the spray is poor and the flame will not light or stay lit.
• A valve is shut or the tank vent is blocked. A closed supply valve or a vent clogged with debris can stop oil flowing even when the tank is full.

Burner Faults: Why The Flame Won’t Appear Or Stay Lit

• The burner is sitting in lockout. Until it is reset, it will not try again. Reset it once, and if it locks out again, stop there.
• The flame sensor is dirty or has failed. If it cannot see a flame, the burner shuts down after a few seconds.
• The electrodes are worn. Wear, soot or a wrong gap give a weak spark and a lazy ignition.
• The ignition transformer has failed. The burner purges and then locks out with no spark at all.
• The motor or its coupling is at fault. A failed capacitor or a seized coupling leaves the motor humming and the fan or pump stationary.
• The oil pump is worn. A tired pump struggles to build pressure, or its internal strainer has clogged.
• The solenoid valve is sticking. It should open to let oil through to the nozzle. If it does not, nothing is sprayed.
• The control box has failed. The unit that runs the start-up sequence can fail with age or after a power surge.

Controls, Safety Devices And System Faults

• No power or no call for heat. A switched-off isolator, a thermostat that is not asking for heat or a timer reset by a power cut looks like a dead burner.
• The overheat cut-out has tripped. It should not be reset until the reason for the overheating is found.
• The fire valve has closed. It shuts off oil when it senses excess heat. An engineer should check why before reopening it.
• Low system pressure. On sealed-system installations, pressure that has fallen too low can stop the boiler running.
• A faulty zone valve. A valve that fails to open means the boiler is never told to fire.
• A frozen condensate pipe. On condensing models, a frozen drain in winter can shut the boiler down.
• A blocked flue or air supply. If the burner cannot breathe or exhaust properly, it may lock out.
• Very cold weather. Oil in exposed pipework or an above-ground tank can thicken in severe cold and restrict flow.

How To Tell Whether The Problem Is Your Oil

The tank is the likely cause when the boiler runs for a few days after a service and then fails again, when the tank is old or steel, or when its cover is missing or damaged. A lockout shortly after a delivery can also be a sign that disturbed sediment has reached the filter.

What You Can Do Yourself, And What To Leave Alone

Looking at the tank gauge, the isolator, the fuse and the heating controls is sensible, and so is a single reset. The oil line, the filter, the nozzle and the burner itself are for a qualified engineer. Oil does not forgive repeated failed starts the way gas often does.

Worcester Bosch Oil Boiler Repair In Leicester, Coventry And Hinckley

Our boiler repair service will find out whether the fault is in the tank, the pipework or the burner, and we will explain what we found before any work starts. We cover Leicester, Coventry, Rugby, Loughborough, Hinckley, Nuneaton and Tamworth. Keeping up with annual oil boiler servicing catches many of these faults before they cause a lockout.

If the boiler is old and the repairs are mounting, our guide on whether to repair or replace your boiler will help you weigh it up, and we can quote for oil boiler installation if replacement makes sense. We also offer Worcester Bosch boiler installation services, so a new Worcester can be fitted by the same team.

Get Your Worcester Bosch Looked At

Drop us a line through the contact form and tell us what your boiler is doing. We will take it from there.

Worcester Bosch Oil Boiler Lockout FAQs

Is a lockout the same as a breakdown?

Not always. A lockout is a safety shutdown, and sometimes the cause is as simple as an empty tank. It is still worth finding out why it happened.

Can water in the oil tank stop my boiler working?

Yes. Water encourages sludge, which clogs the filter and nozzle and can leave the burner unable to light.

How often should I check my oil tank?

Look at the gauge, the cover and the tank itself regularly, and ask your engineer to cast an eye over it at the annual service.

Why did my boiler fail just after an oil delivery?

A delivery can stir up sediment or leave air in the line. Either can interrupt the supply until the filter is cleaned or the line is bled.