How to Reset a Worcester Bosch Boiler

Worcester Bosch boilers are among the most common in UK homes, and the Greenstar range in particular is built to be easy to reset from the front panel. If your heating or hot water has dropped out, a single reset will often bring it back to life. The trick is knowing how to do it safely, and recognising when a reset will not fix the problem and you need a professional.

This guide covers Greenstar combi, system and heat-only models. It does not cover anything behind the boiler casing, which is gas work and must only be touched by a Gas Safe registered engineer.

Before you reset: a 30-second check

A reset clears a lockout, but it is worth a quick look first so you are not resetting blindly:

• Is there power? Check the boiler's fused spur or plug, the consumer unit (fuse box) and that the display is lit at all.
• Is the programmer/thermostat calling for heat? A room thermostat set below room temperature, or a programmer in an "off" period, will look like a fault when nothing is wrong.
• What does the screen say? Most Greenstar models show a fault code (often an "EA", "E9", "1006" or similar) and many have a red light or a flame symbol with a cross. Note it down before you reset, as it tells you whether resetting is the right move.

How to reset a Greenstar boiler

On most current Greenstar models (such as the Greenstar i, Greenstar 8000 and CDi Compact ranges) the reset is built into the front controls:

1. Find the reset button. On many models it is a dedicated button marked with a flame symbol or the word "reset"; on others, including some 8000 models, you press and hold the central "r" / reset button or the flame button for a few seconds.
2. Press and hold it for around 3 to 5 seconds until the display changes or the fault clears.
3. Wait. The boiler will run through its ignition sequence; you may hear the fan and a few clicks. Give it up to a couple of minutes to relight and settle.
4. Turn on the heating or run a hot tap to confirm normal operation has returned.

If your model has a small rotary dial rather than buttons, turning it to the reset position (sometimes marked with the flame-and-arrow symbol) does the same job. When in doubt, the exact button for your model is shown in the Worcester Bosch user guide that came with the boiler, or on the inside of the front flap on many units.

The "reset once" rule

A boiler that resets, runs for a while, then locks out again is also telling you there is an underlying fault. Note how long it runs before failing, as that detail is genuinely useful to whoever attends.

Low pressure: the most common reason for a "fault"

A surprising number of Worcester "faults" are simply low water pressure, and this is something you can safely fix yourself. Check the pressure gauge on the front of the boiler:

• When the system is cold, pressure should sit at roughly 1 to 1.5 bar.
• As the heating warms up it will rise, often towards 2 bar, which is normal.
• Below about 1 bar (often shown by a low-pressure code or a flashing gauge) the boiler may refuse to fire.

To top up, use the filling loop or, on many Worcester models, the integrated filling key underneath the boiler. Slot the key in, open the valves slowly and watch the gauge climb back to about 1.2 bar, then close the valves and remove the key. Once the pressure is back up, a single reset usually clears the fault. If you are unsure where your filling loop is, our guide on what boiler cover includes explains why many homeowners prefer to leave repressurising to an engineer visit.

If pressure drops again within days, there is a leak or a failing expansion vessel somewhere in the system. Topping up repeatedly is a workaround, not a fix, so book an engineer to find the cause.

Common Worcester Bosch fault indicators

Greenstar models use alphanumeric codes. You don't need to memorise them, but a few are worth recognising:

What you see	Likely meaning	Safe to do yourself?
Low-pressure code / gauge below 1 bar	System pressure has dropped	Yes — repressurise via the filling key/loop, then reset
Reset / lockout indicator after a power cut or short outage	Boiler tripped and needs restarting	Yes — reset once
EA-type ignition codes, or repeated lockouts	The boiler is failing to ignite or detect the flame	No — reset once; if it returns, call an engineer
Codes pointing to the fan, gas valve, flue or heat exchanger	Internal component fault	No — Gas Safe engineer only

Codes vary between model ranges, so always cross-check yours against the Worcester Bosch manual for your exact model. A persistent code that points to gas, ignition or the flue is not something to chase yourself.

When to stop and call a Gas Safe engineer

Reset cleared the problem and everything is running normally? Great, no further action needed. Call a Gas Safe registered engineer (check the register at gassaferegister.co.uk) if any of the following apply:

• The boiler locks out again immediately, or repeatedly after running for a short time.
• You see ignition, flue, fan, gas-valve or heat-exchanger fault codes.
• There is a smell of gas, sooty marks, or yellow/orange flames rather than blue.
• Pressure keeps dropping despite topping up, suggesting a leak.
• You hear banging, whistling or "kettling" noises, or water is leaking from the unit.

Never remove the boiler casing, and never touch the gas valve, gas pipework, the flue, the pressure-relief valve or the sealed combustion circuit. That is gas work, full stop, and it is illegal as well as dangerous for anyone who is not Gas Safe registered.

The cost of a one-off call-out vs cover

A single engineer call-out for a boiler that won't reset typically runs from around £80 to £150 for the visit alone, before any parts (indicative, 2026). If the fault is a failed component the bill can climb well past that. This is exactly why many households take out boiler cover: a fixed monthly cost in exchange for repairs, parts and labour when things go wrong. If you're weighing it up, compare what's included and what's excluded across providers before you commit, and have a look at our roundup of the best boiler cover and cheaper budget policies.

Frequently asked questions