Boiler fault codes
Worcester E9 Fault Code: An Overheat Lockout
Published
Worcester Bosch display
E9
What it means
An overheat safety device inside the boiler has tripped and the boiler has locked out to protect itself. The three-digit cause code shown with E9 says which sensor tripped and why.
Safe to check yourself
- Read the pressure gauge: Worcester asks for 1 to 1.5 bar on a cold sealed system
- Make sure the valves under the boiler and on the radiators are open
- Bleed radiators that are cold at the top, then recheck the pressure
- Top up through the filling loop if you know how and the pressure is low
- Press and hold reset for about five seconds, once
Call an engineer if
- You smell gas: ventilate, shut off the gas at the meter if safe, do not touch switches, and call 0800 111 999 from outside
- E9 returns after one reset with the pressure correct
- You hear the boiler kettling, banging or boiling before it locks out
- The cause code is 220 or 221, which points at a sensor fault
E9 on a Worcester Bosch boiler means one of its overheat safety devices has tripped, so the boiler has shut down and locked out. Low water pressure, a closed valve, trapped air or a stuck pump are the usual reasons the water got too hot. Check the pressure, reset once, and call if it returns.
What does E9 mean on a Worcester boiler?
Worcester fits temperature limiters that cut the burner if water or flue gas gets hotter than it should. When one trips, the display shows E9 and the reset button flashes. It is a locking fault, so nothing restarts until the reset is pressed.
Newer Greenstar boilers show a cause code next to E9, and the exact list depends on the model. Worcester manuals give these meanings:
- 219: safety sensor temperature too high (the water really did overheat)
- 220 or 221: safety sensor short circuit or open circuit (usually a sensor or wiring fault, not a true overheat)
- 224: the maximum temperature thermostat, or safety temperature limiter, has tripped
- 276 on some Greenstar i models: primary flow temperature went above 95°C
On the Greenstar 8000 range the same condition shows as 224 on its own, without the E9 prefix. If your manual lists a different meaning for your model, go with the manual.
Why did my Worcester boiler overheat?
Worcester's own fault-finding for E9 starts with the water, not the electronics. Its first checks are whether a sealed system is between 1 and 2 bar (or whether an older open-vented system has enough water in its feed and expansion tank) and whether the pump has seized. Water that is not moving through the heat exchanger boils fast.
After that come the electrical checks: a loose lead on the flue or flow limiter, the limiters themselves, the harness and a fuse on the control board. Sludge and scale in the heat exchanger are the other common culprit on older boilers, because they slow the flow and create hot spots.
What can I safely check tonight?
Everything below is outside the casing. Look at the pressure gauge first. If it is under 1 bar, the low Worcester pressure guide shows how to top up, and if you cannot find the filling key our boiler pressure repair page covers the next step.
Check the isolating valves under the boiler are open, particularly if anyone has recently worked on the heating or changed a radiator. Worcester lists "open the closed valve in the heating circuit" as a remedy for 224. Bleed any radiator that is cold at the top, recheck the pressure, then press and hold reset for about five seconds.
Reset once. Overheat trips exist to stop damage to the heat exchanger, and resetting over and over only restarts the boiler into the same fault.
When does E9 need an engineer, and what does it cost?
If the pressure is right and E9 comes back, something inside needs testing: the pump, the limiters, or a blocked heat exchanger. Replacing a limiter is a small job. A seized pump can sometimes be freed, but if it will not restart it means draining the boiler and fitting a new pump, and a sludged-up system may need a flush before the fault stays away. The engineer will explain which it is and agree the repair price on site before starting, after the £60 call-out. Our emergency plumbing prices set out how that works.
To get an engineer out at any hour, book a Worcester boiler repair. Gas work is carried out by Gas Safe registered engineers.
Questions people ask
Is the E9 fault dangerous?
The lockout is the boiler protecting itself, so the fault is not dangerous while the boiler is off. Do not keep resetting a boiler that is banging or boiling. If you smell gas, open windows, turn off at the meter if safe, get out and call 0800 111 999.
Can low pressure cause E9 on a Worcester?
Yes. Too little water in the system is one of the first things Worcester tells engineers to rule out, because the boiler overheats when water is not circulating properly.
Is E9 the same on every Worcester boiler?
The meaning, an overheat safety trip, is the same. The cause code after it differs between models, and the Greenstar 8000 shows 224 without E9. The Worcester fault code index lists the other codes.