What it means
On Greenstar i ErP and Si, CDi and i System Compact ErP boilers you see E9 with 224 under it, which Worcester describes as the flue or high-limit thermostat being activated. Greenstar 4000, 8000 Life and Worcester 2000 boilers show 224 on its own.
What to check, in order
- Check the pressure gauge
Low system pressure is one of the causes Worcester lists, and its manual says the boiler may stop below 1 bar.
- If it's low, top up and reset
Fill to 1.5 bar with the filling link, then hold the reset button for 3 seconds.
- Otherwise, leave it to an engineer
If the pressure was fine, or E9 comes back, don't try to put it right yourself. Worcester's manual says to contact a Gas Safe registered engineer.
When to call a Gas Safe engineer
Worcester's service booklet lists a seized pump, a faulty flow or flue safety limiter, a wiring fault, a blown fuse and a faulty control board among the causes.
A repair visit will usually check the pump, the flow of water round the system and the overheat thermostat.
- Note the model and serial number. They're on a label on the data badge, usually under the boiler or behind the front cover.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Good to know
- On an open-vented system, with a feed and expansion tank in the loft, there's no pressure gauge to check. Worcester's engineers check the tank has enough water in it.
Quick answers
What does the Worcester Bosch E9 fault code mean?
A safety thermostat or temperature limiter has tripped because part of the boiler got too hot, so the boiler has locked out. On Greenstar i ErP and Si, CDi and i System Compact ErP boilers you see E9 with 224 under it, which Worcester describes as the flue or high-limit thermostat being activated. Greenstar 4000, 8000 Life and Worcester 2000 boilers show 224 on its own.
Can I fix Worcester Bosch E9 myself?
Engineer only (5 minutes to check the gauge). Start with: check the pressure gauge; if it's low, top up and reset; otherwise, leave it to an engineer. Worcester's service booklet lists a seized pump, a faulty flow or flue safety limiter, a wiring fault, a blown fuse and a faulty control board among the causes.
Is Worcester Bosch E9 worth repairing?
Deal with it now. It's a safety shutdown because the boiler got too hot. If one reset doesn't hold, get an engineer in.
Checked against
- Worcester Bosch Greenstar CDi Classic user instructions (PDF)
- Worcester Bosch Greenstar CDi Classic engineer's service booklet (PDF)
- Worcester Bosch Greenstar i ErP installation and servicing instructions (PDF)
- Worcester Bosch Greenstar Si Compact ErP installation and servicing instructions (PDF)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.