Worcester Bosch boiler fault codes — what they mean and what to do

Seeing a code flash up on your Greenstar? Here's what it's telling you, what's safe to check yourself, and when to call us out.

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What a fault code is telling you

Your Worcester Bosch boiler watches itself. When something's not right, it stops and shows a code on the display so you know roughly what's wrong.

Most codes look scary but aren't. Some point to simple things you can sort in a few minutes, like low pressure or a one-off glitch.

Others mean a part has failed and needs a Gas Safe registered engineer. We'll always tell you which is which, and never ask you to touch anything to do with gas.

Codes vary a little between Greenstar models, so check your manual for the exact wording. The most common ones are below.

Common Worcester Bosch fault codes

Fault code	What it means	What to do
EA	No flame detected. Often a gas supply or ignition issue.	Check your other gas appliances work. Reset once. If it returns, book a Gas Safe registered engineer. Smell gas? Call 0800 111 999.
E9	Boiler has overheated and the safety limiter has tripped.	Don't reset an E9. Check pressure and that radiator valves are open, then book a Gas Safe registered engineer. Resetting an overheat fault isn't recommended.
C6 / C7	Fan fault — the fan isn't running at the right speed on start-up.	This needs testing. Reset once, then book a Gas Safe registered engineer if it sticks.
A1	Pump stuck or running dry, often due to a leak.	Check around the boiler for water. Don't run it dry — book an engineer to look at the pump.
A7	Hot water sensor not working.	You may still have heating. Book an engineer to replace the sensor.
D5	Condensate pump or pipe fault. Often a blocked or frozen condensate pipe (on some CDi models it's a service reminder).	In cold weather, check for a frozen external condensate pipe and thaw it gently with warm (not boiling) water if it's safe to reach. Otherwise book a Gas Safe registered engineer.
H07 / CE (low pressure)	Water pressure too low.	Re-pressurise to about 1.0–1.5 bar using the filling loop. Repeat drops mean a leak — book an engineer.
CE (sensor)	Flow temperature sensor or wiring fault on some models. Note: CE can mean low pressure or a sensor fault depending on your Greenstar model — check your manual.	If it's the sensor fault, this isn't a DIY fix. Book a Gas Safe registered engineer.
F7 / FA / FB	Flame-signal and gas-valve faults. F7/FA are false-flame signals; FB is a gas-valve leak-test failure, so the gas valve or flame circuit may be involved.	Don't reset beyond once. Book a Gas Safe registered engineer. If you smell gas, call 0800 111 999, open windows, turn off the gas at the meter, don't touch electrical switches, and leave the property.
E5	Flow sensor over-temperature.	Check pressure and that the system isn't airlocked. If it persists, book an engineer.

The three codes we get asked about most

EA — no flame detected

This is the one most people see. The boiler tried to light and couldn't find a flame, so it shut off to stay safe.

First, check your other gas appliances. If the hob won't light either, it could be your gas supply. Reset the boiler once using the reset button.

If EA comes straight back, stop there. The ignition or gas valve may need a Gas Safe registered engineer. If you smell gas at any point, call 0800 111 999.

E9 — overheating

E9 means the boiler got too hot and its safety cut-out tripped. It's doing exactly what it should.

Low pressure, trapped air, sludge or a tired pump can all cause it. Check your pressure gauge and make sure radiator valves are open.

Don't reset an E9. Repeatedly resetting an overheating boiler can damage the heat exchanger, and the lockout is a genuine safety trip. The heat exchanger or pump may need attention — that's an engineer job.

H07 and CE — low pressure

These are the friendliest faults to see. Your system pressure has dropped too low for the boiler to fire.

Find the filling loop — the silver braided hose under the boiler. Open both valves slowly until the gauge reads between 1.0 and 1.5 bar, then close them.

If pressure keeps falling after a top-up, you've probably got a small leak somewhere. We'll come and fix it for you.

Safe checks before you call anyone out

These are the only things worth trying yourself. If a code involves gas, skip straight to a Gas Safe registered engineer.

Check the pressure gauge — it should sit around 1.0 to 1.5 bar when cold.
Top up via the filling loop if pressure's low, then close the valves fully.
Make sure the boiler has power and the programmer is set to come on.
Check your thermostat is calling for heat and the batteries aren't flat.
Confirm your other gas appliances work, to rule out a wider supply issue.
Reset the boiler once — just once. Don't keep doing it if the code returns, and don't reset an E9 overheat fault at all.
If you smell gas, stop everything. Call 0800 111 999, open windows, turn off the gas at the meter, don't touch electrical switches, and leave the house.

When a code won't clear — how Smart Plan helps

If you've checked the simple stuff and the code's still there, the next step is a Gas Safe registered engineer. That's where we come in.

Smart Plan is a service plan, not insurance. You've got two easy options when your boiler plays up.

Need it fixed now?

Book a one-off repair and we'll come and fix it for you. One of our Gas Safe registered engineers diagnoses the fault and gets your heating back on.

Want cover for next time?

Take out an ongoing Smart Plan boiler module and you're sorted when the next code appears. Parts and labour are included up to your cover limit.

Cover is modular, so you only pick what you want — don't pay for what you don't use. Boiler cover runs up to £500 per year if your boiler's under 7 years old, or up to £200 if it's older. A £95 call-out fee applies.

We've looked after over 15,000 customers, we've been trading since 2014, and we're rated Excellent on Trustpilot. When a fault code won't budge, we'll come and fix it for you.

Worcester Bosch fault code FAQs

Is boiler cover the same as insurance?

No — it's a service plan, not insurance. You pick the cover modules you want, and when something breaks we send a Gas Safe registered engineer to fix it, with parts and labour included up to your cover limit.

How many times should I reset my boiler?

Just once, and not at all for an E9 overheat fault. If the same code comes straight back after a reset, stop. Repeated resets can hide a real fault. Book a Gas Safe registered engineer instead.

Can I fix a Worcester Bosch fault code myself?

Only the safe basics — topping up pressure, checking the thermostat, or a single reset. Anything involving gas, the fan, or internal parts needs a Gas Safe registered engineer. Never attempt a gas repair yourself.

What does it mean if pressure keeps dropping after I top it up?

It usually points to a small leak in the system. Keep an eye on the gauge and book an engineer to trace it. We'll come and fix it for you.

What does a D5 code mean on a Worcester Bosch boiler?

On most Greenstar models, D5 points to a condensate pump or pipe fault — often a blocked or frozen condensate pipe. In cold weather, check for a frozen external pipe and thaw it gently with warm (not boiling) water if it's safe to reach. On some CDi models it's a service reminder. If you're unsure, book a Gas Safe registered engineer.

What should I do if I smell gas?

Call the National Gas Emergency Service on 0800 111 999 straight away. Open your windows, turn off the gas at the meter, don't touch any electrical switches, and leave the property.

Does Smart Plan cover Worcester Bosch boilers?

Yes. Our boiler module covers most makes, including Worcester Bosch Greenstar. Cover runs up to £500 per year if your boiler's under 7 years old, or up to £200 if it's older, with a £95 call-out fee.

Code still showing? We'll come and fix it for you.

Book a one-off repair or set up an ongoing Smart Plan boiler module. A service plan, not insurance — parts and labour included up to your cover limit.