To reset a Worcester Bosch boiler, find out which model you have. On newer Greenstar 4000 and 8000 models, press the reset button on the control panel. On some older Greenstar i, Ri and Si models, the reset is a position on the boiler control knob rather than a button: check your manual, then hold it there for a few seconds and turn it back. A flashing blue light usually means the boiler has locked out with a fault: check the code on the display, fix the cause if you can (for example low pressure), then reset. If it locks out again, call a Gas Safe engineer.
Worcester Bosch is one of the most common boiler brands in UK homes, and "how to reset my Worcester boiler" is one of the most-searched heating questions every winter. This guide covers reset steps for each model family, what the lights and symbols mean, common fault codes, and when a reset isn't the answer. For other brands, see our heating guides.
Before you reset: check these first
A reset only clears the lockout; it doesn't fix the cause. Check these quick things first, or the boiler will simply lock out again:
- Boiler pressure. It should be roughly 1–1.5 bar when cold (check your manual). Low pressure is the most common reason for a Worcester lockout. See how to top up a Worcester boiler.
- Gas supply. Does the hob work? Has a prepayment meter run out of credit?
- Frozen condensate pipe in cold weather (the plastic pipe running outside).
- Power. Is the display lit? Is the fused spur switch next to the boiler on?
If you smell gas, don't reset the boiler. Call the National Gas Emergency number on 0800 111 999 immediately, turn the gas off at the meter if it's safe to do so, and open the windows.
How to reset a Worcester Greenstar 4000 or 8000
Newer Worcester boilers (the Greenstar 4000, 8000 Life, 8000 Style and similar) have a digital display and a dedicated reset button.
- Note the fault code shown on the display.
- Fix the cause if it's something you can do (for example top up low pressure).
- Press the reset button on the control panel. On some models you press and hold it for a few seconds; check your user manual.
- Wait a minute or two while the boiler restarts and tries to fire.
How to reset an older Worcester Greenstar i, Ri or Si
Some older Greenstar models have dials with a "reset" position rather than a reset button. The exact method varies by model, so follow your user manual.
- Find the boiler temperature control knob (often the left-hand dial).
- Turn it to the "reset" position and hold it there for a few seconds (as your manual describes).
- Turn it back to your normal temperature setting.
- Wait for the boiler to restart.
The exact position varies between models, so check the symbols on your dial or your user manual if you're not sure.
What does a flashing blue light mean on a Worcester boiler?
On many Worcester Greenstar boilers, a steady blue light simply shows the boiler has power or the burner is on. A flashing blue light, usually with a fault code on the display, generally means the boiler has detected a fault and locked out.
What to do:
- Read the code on the display (for example EA 227 or CE 207).
- Check the common causes in the table below.
- Reset once you've dealt with anything you can fix.
- If the blue light keeps flashing after a reset, call a Gas Safe engineer and give them the code.
Common Worcester Bosch fault codes
| Code | What it usually means | What you can do |
|---|---|---|
| EA 227 | Ignition failure: no flame detected | Check gas supply and condensate pipe, then reset |
| CE 207 | Low water pressure | Top up to 1–1.5 bar, then reset |
| E9 224 | Overheat (high-limit or safety temperature limiter) | Check pressure and that radiators heat up; if it repeats, engineer |
| D5 / D3 | Meaning varies by model (sensor, condensate or connection faults) | Check your manual; engineer |
| Four-digit codes (e.g. 1101) | Newer Greenstar models use 4-digit codes | Look up the code in your manual. Check the pressure first, as low pressure is the most common cause |
Codes vary between models, so your user manual (or the Worcester Bosch website) is the definitive list for your boiler.
Write down the exact code and when it happens (only for hot water, only in frosty weather, after the heating has been running for a while). That information helps an engineer diagnose the fault much faster.
How to increase pressure on a Worcester boiler without a key
Many older Worcester Greenstar combis use a key-operated filling link under the boiler: you insert a small key and turn it to let water in.
- Look for the key first. It's often clipped underneath the boiler, or kept with the manual and installation paperwork.
- Lost the key? Replacement filling keys for your model are widely available and cheap.
- Newer models have a keyless filling link: a lever or tap underneath the boiler, with no key needed.
- Some homes have an external filling loop: a braided hose with two valves on the pipes below the boiler.
Don't try to force the filling link open with pliers or screwdrivers. If you can't find a way to top up, an engineer can do it in minutes.
Worcester boiler no hot water (but the heating works)
- Check the hot water temperature dial hasn't been turned down.
- Run a hot tap at a decent flow: combis need a minimum flow rate to fire for hot water.
- If you have a system or regular boiler with a cylinder, check the hot water programmer is on.
- If there's no hot water from any tap and no fault code, the diverter valve may be faulty, which is an engineer job.
Worcester boiler not firing up or not turning on
- No display at all: check the fused spur, your consumer unit, and whether there's a power cut.
- Display on but won't fire: check the room thermostat and timer are calling for heat, the pressure is around 1–1.5 bar, and there's gas.
- Fault code showing: follow the steps above, then reset.
When resetting doesn't work
Stop resetting after one or two attempts if the boiler locks out again. Repeated resets won't fix a worn ignition electrode, a faulty fan or a failed sensor, and you could mask a real problem. Book a Gas Safe registered engineer; Worcester Bosch also offers its own engineer service.
Typical UK costs: call-out and diagnosis £60–£120; ignition electrode £80–£180; diverter valve £150–£300; fan £200–£350; PCB £300–£500.
FAQs
Where is the reset button on a Worcester boiler?
On newer Greenstar 4000 and 8000 models, it's a button on the front control panel. Some older Greenstar models use a reset position on the control knob instead; your user manual shows which.
Why does my Worcester boiler keep needing a reset?
Usually because of low pressure, a frozen condensate pipe, a gas supply problem or a worn part such as the ignition electrode. If it needs resetting more than once or twice, get it checked.
What does a flashing blue light mean on a Worcester boiler?
It usually means the boiler has locked out because of a fault. Check the fault code on the display, fix the cause if you can, and reset.
Is it safe to reset a Worcester boiler?
Yes, resetting is a householder action described in the user manual. Don't reset if you smell gas, and don't remove the boiler casing.
What does EA 227 mean on a Worcester boiler?
EA 227 means the boiler couldn't detect a flame when trying to light, so it's an ignition failure. Check the gas supply and condensate pipe, then reset. If it repeats, call an engineer.
Why is my Worcester boiler not firing up?
Common causes are low pressure, no gas, a frozen condensate pipe, the thermostat or timer not calling for heat, or a fault such as a worn ignition electrode.
- Newer Worcester models: press the reset button. Some older models use a "reset" position on the knob: check your manual.
- A flashing blue light usually means a lockout: read the code first.
- Check pressure, gas and the condensate pipe before resetting.
- If it locks out again, call a Gas Safe engineer.
