Worcester Bosch boilers are among the most reliable on the market, which is why there are so many of them in Cornwall and Devon and why the same handful of problems come up again and again. The most common are low pressure, a frozen condensate pipe in winter, ignition faults shown as EA or a flashing blue light, overheat shown as E9, and fan or flue faults shown as C6 and D5. Low pressure and a frozen condensate pipe are things a homeowner can deal with. The rest need a Gas Safe engineer, and a boiler showing a fault should be reset once at most.
This guide runs through the faults engineers see most on Worcester Bosch Greenstar and older ranges, what each means and what to do.
Low pressure and the boiler not firing
Greenstar boilers show a pressure warning, and older models simply refuse to fire, when the system drops below about 0.5 bar. Top up to around 1.3 bar via the filling loop, which on many Worcester models is a built-in key and valve under the boiler. If the pressure keeps falling, there is a leak or the expansion vessel is flat. Our guide to a boiler losing pressure explains what to look for.
Frozen condensate pipe
In a cold snap, the most common Worcester call-out by a distance. The boiler gurgles, fails to ignite and shows an ignition code. Thaw the external condensate pipe gently with warm water and reset once. Insulating the pipe stops it happening again. Our guide to a frozen condensate pipe covers it in detail.
EA: ignition fault
EA, or a blue light flashing on older models, means the boiler failed to light or lost its flame. Check the gas is on, the condensate pipe is clear and the pressure is fine, then reset once. Persistent EA is an ignition electrode, lead, gas valve or flue issue for an engineer.
E9: overheat
The boiler got too hot because water was not circulating, or a sensor failed. Check the pressure and that radiator valves are open, let it cool, reset once. Repeated E9 points to a pump, a blocked heat exchanger or a sensor.
C6, C7, D5, E2, E5: fan, flue and sensor faults
C6 and C7 relate to the fan not running at the expected speed, often a failing fan or a blocked flue. D5 and E2 are sensor faults. E5 is another overheat variant. All are engineer-only.
A1: pump running dry or blocked
The pump is running but sensing no flow, usually low pressure, air in the pump or sludge. Check pressure, bleed, reset once.
Hot water lukewarm or going hot and cold on a Greenstar combi
Usually a scaled plate heat exchanger or a sticking diverter valve, both routine repairs. Our guide to a combi boiler going hot and cold explains the diagnosis.
Kettling or banging
Scale or sludge on the main heat exchanger. A flush and a magnetic filter cure it. Our guide to a boiler making noises matches sounds to causes.
Water leaking from under the boiler
Often the pressure relief valve discharging internally, a worn pump seal or a heat exchanger leak. Turn the boiler off and call an engineer; water and electronics do not mix.
Blue light flashing or boiler locked out on a Greenstar
On Greenstar models a flashing blue light with a code on the display means the boiler has locked out. Older Worcester boilers without a display use the blue light alone, and the number of flashes indicates the fault. In both cases the first three things to check are the same: system pressure, the condensate pipe in cold weather and whether the gas supply is on. Those three account for the majority of Worcester lockouts in Cornwall and Devon, and a homeowner can clear all of them. Anything beyond that, especially a fan, sensor or gas valve code, is a job for a Gas Safe engineer with the casing off.
What you can safely do
- Top up the pressure.
- Thaw a frozen condensate pipe.
- Check the gas supply and the programmer.
- Reset once and note the code.
Our guide to how to reset a boiler explains the safe way.
How DCI Boilers can help
DCI Boilers repairs Worcester Bosch boilers across Cornwall and Devon, with Gas Safe registered engineers who carry the common Greenstar parts and quote a fixed price before starting. Book boiler repairs, or for a cold house our emergency boiler call-out runs around the clock. Annual boiler servicing keeps a Worcester running the way it was built to.
Need help now? Call DCI Boilers on 07888 862 603 or get a free quote.
Frequently asked questions
What does the flashing blue light mean on a Worcester boiler?
On older models it signals a lockout, usually an ignition fault. Check gas, pressure and the condensate pipe, then reset once.
What is EA on a Worcester boiler?
An ignition fault. The boiler could not light or lost its flame. One reset; if it returns, an engineer is needed.
Why is my Worcester boiler pressure low?
Sealed systems lose a little pressure over time, and more if there is a leak. Top up to about 1.3 bar and watch whether it drops again.
Are Worcester Bosch boilers reliable?
Very. They top engineer surveys year after year. The faults above are the same ones every boiler gets, and most are simple to fix.