Worcester Bosch 3 Long Flashes Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch 3 Long Flashes fault code mean?
The 3 long flashes fault code appears on older Worcester Bosch Greenstar models that use a flashing blue indicator light rather than a digital display — such as the Greenstar Ri, 24i Junior, and 28i Junior. On these boilers, faults are communicated through a light sequence: four quick flashes followed by a five-second pause, then a series of slower, longer flashes. Three of those longer flashes signals an ignition or flame-detection lockout. In plain terms, the boiler attempted to light the burner, either failed to ignite at all or could not confirm a stable flame was present, and has shut itself down safely. This is a locking fault, meaning the boiler will not restart on its own — it requires a manual reset once the root cause has been identified and resolved. On newer Worcester Bosch models with a digital screen, the equivalent fault typically appears as an EA code (most commonly EA 227), so if you've landed here via that route, the diagnosis and fixes below still apply.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Dirty or failed flame-sensing electrode Common
The flame ionisation rod sits inside the burner chamber and passes a tiny electrical signal through the flame to confirm ignition has taken place. If it becomes coated in soot or carbon deposits — which happens gradually over years of use — the control board receives no confirmation signal and shuts the gas off as a precaution. A cracked or worn electrode has the same effect. This is by far the most frequent cause of this fault on older Greenstar models.
- No or restricted gas supply Common
If the gas supply to the boiler is interrupted — whether due to a closed isolation valve, a wider network outage, or a prepayment meter running empty — the boiler will attempt to ignite, find nothing to burn, and lock out. Check whether other gas appliances in the home such as a hob or gas fire are working normally. If they are not, the issue is upstream of the boiler entirely.
- Frozen or blocked condensate pipe Common
In cold weather, the condensate pipe that carries acidic waste water from a condensing boiler to the drain can freeze solid, particularly where it runs externally. A blockage here causes combustion gases to back up and the boiler to lock out. This fault becomes noticeably more common between November and February. If temperatures have dropped below freezing recently, this should be checked early.
- Faulty or damaged ignition electrode or lead Sometimes
The spark electrode is a separate component from the flame-sensing rod. It generates the initial spark to light the gas. If the electrode tip is worn, the ceramic insulator is cracked, or the high-tension lead connecting it to the PCB is damaged, the burner simply will not ignite. A Gas Safe engineer can test the spark visually and with a meter.
- Flue obstruction Sometimes
If the flue terminal on the outside wall is partially blocked — by a bird nesting nearby, debris, or ice in very cold conditions — combustion gases cannot escape properly. This disrupts the air-to-gas ratio at the burner, preventing stable ignition and triggering a lockout.
- Low system pressure Sometimes
Worcester Bosch Greenstar boilers require the system water pressure to sit between 1 and 1.5 bar for safe operation. If pressure has dropped significantly below 1 bar — visible on the pressure gauge on the boiler — the unit may refuse to fire or lock out mid-cycle. Pressure can drop gradually due to small leaks or simply from normal bleeding of radiators.
- Faulty PCB or spark generator module Rare
The printed circuit board (PCB) orchestrates the entire ignition sequence — triggering the spark, opening the gas valve, and reading the flame signal back. If the board itself is faulty, or the spark generator module it controls has failed, the boiler may behave erratically or lock out consistently even when gas supply and electrodes are fine. PCB faults are less common but more expensive to resolve.
- Faulty gas valve Rare
The modulating gas valve controls the flow of gas to the burner. If it fails to open correctly — or the valve relay or wiring to it is damaged — no gas reaches the burner and ignition cannot occur. Gas valve faults are serious and must only be diagnosed and replaced by a Gas Safe registered engineer.
How to fix it
- Check that other gas appliances in your home are working DIY safe
Turn on a gas hob burner or another gas appliance to confirm gas is flowing to your property. If nothing is working, contact your gas supplier or check whether a prepayment meter needs topping up. If gas is available elsewhere in the home, move on to the next step.
- Check and top up the boiler's system pressure if needed DIY safe
Locate the pressure gauge on the front of the boiler — it is usually a small dial or analogue display showing a reading in bar. It should read between 1 and 1.5 bar. If it is below 1 bar, use the filling loop (a small braided hose beneath the boiler connecting the two valves) to slowly introduce water until the gauge reads approximately 1.2 bar, then close both valves. If you are unsure how to use the filling loop safely, consult the boiler manual or call an engineer.
- Check for a frozen condensate pipe in cold weather DIY safe
If outdoor temperatures are below freezing, go outside and find the white plastic condensate pipe that exits the boiler through an external wall and typically runs down to a drain. If it feels solid or you can see ice, it has frozen. Carefully pour warm (not boiling) water along the length of the pipe to thaw it — a hot water bottle pressed against the pipe also works well. Once thawed, attempt to reset the boiler. This single step resolves a significant proportion of winter lockouts without any engineer involvement.
- Reset the boiler once DIY safe
Press and hold the reset button for approximately three seconds until the indicator light responds. On some older Greenstar models, the reset is triggered by rotating the temperature dial to the reset position and holding it. Allow the boiler to complete its ignition sequence — this can take up to 30 seconds. If it fires successfully, monitor it over the next hour. Do not reset more than two or three times in total; repeated resets on a persistent fault will not fix the underlying problem and can cause further damage to components.
- If the fault returns or the boiler fails to ignite, call a Gas Safe registered engineer Gas Safe engineer
Persistent 3 long flashes after a reset, or an immediate re-lockout, indicates a fault that requires professional diagnosis. A Gas Safe engineer will inspect and test the flame-sensing electrode, ignition electrode and lead, gas valve operation, flue integrity, and the PCB. Do not continue resetting the boiler repeatedly while waiting for the engineer. If you smell gas at any point, do not attempt a reset — turn off the gas at the meter and call the National Gas Emergency Service on 0800 111 999 immediately.
Parts you may need
- Flame ionisation (sensing) electrode · from £35
- Ignition spark electrode · from £30
- Ignition lead (high-tension lead) · from £20
- Gas valve · from £120
- Printed circuit board (PCB) · from £180
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £80–£220, depending on the underlying cause.
Frequently asked questions
Can I keep resetting the boiler to get hot water while I wait for an engineer?
It is best to limit resets to two or three attempts at most. If the boiler relights and stays on, that is fine, but if it locks out again immediately or within minutes, further resets will not help and may stress components unnecessarily. Repeated forced ignition attempts with a faulty electrode or gas valve issue can cause additional wear. If you have no hot water or heating and cannot get an engineer quickly, a temporary electric immersion heater or portable electric radiator is a safer workaround.
My boiler shows EA 227 on a digital display — is that the same as 3 long flashes?
Yes, effectively. The EA fault family on Worcester Bosch boilers with digital displays is the modern equivalent of the ignition lockout indicated by 3 long flashes on older non-display models. EA 227 specifically points to a flame-detection failure — the boiler ignited (or attempted to) but the flame sense electrode did not confirm a stable flame within the permitted window. EA 229 relates to a failed ignition attempt where no flame was established at all. Both share the same diagnostic and repair path: electrode inspection, gas supply check, condensate check, and if needed, gas valve or PCB investigation by a Gas Safe engineer.
How much does it cost to fix a 3 long flashes fault on a Worcester Bosch boiler?
For the most common repair — cleaning or replacing the flame-sensing or ignition electrode — you are typically looking at £80 to £160 including parts and labour, and most jobs take under an hour. If the fault turns out to be a gas valve, expect to pay around £180 to £220 all in. A PCB replacement can run to £300 to £400, but an engineer should confirm the diagnosis before ordering one. If your Greenstar is still under warranty, contact Worcester Bosch directly as the repair may be covered at no cost.
My Greenstar is over 10 years old and keeps getting this fault — should I repair or replace?
As a rough guide, if the repair quote exceeds around a third of the cost of a new boiler, or if the same fault has recurred more than twice in 12 months, replacement tends to make better long-term financial sense. Older Greenstar Ri and Junior models can be increasingly difficult and expensive to source parts for. A new Worcester Bosch Greenstar or equivalent A-rated condensing boiler typically costs £1,400 to £2,000 fully installed and will run more efficiently, reducing your gas bills and the risk of further breakdowns.