Worcester Bosch E9 219 Fault: Overheat Lockout — Causes & What To Do

E9 219 indicates the safety temperature sensor recorded a temperature above 105°C, so the boiler locked out to prevent the heat exchanger overheating. It's an overheat lockout — the boiler got too hot, usually because heat wasn't being carried away from the heat exchanger fast enough.

The most common causes, in order of how often we see them:

• • Failed or seized pump — if the pump isn't circulating water, heat builds up in the heat exchanger and the overheat sensor trips. A very common E9 219 cause.
• • Airlock in the system — trapped air can stop circulation in part of the system, causing localised overheating.
• • Blocked or scaled heat exchanger — sludge and limescale restrict flow through the heat exchanger, so it overheats even with a working pump.
• • Frozen condensate — a blocked flue from a frozen condensate can cause flue-gas overheating that trips the safety sensor in cold weather.
• • Blocked system filter — a choked magnetic filter can restrict flow enough to cause overheating.

You can try one reset — if it was a one-off airlock that has cleared, the boiler may run normally. But if the overheat cause remains (a failed pump, blockage, or frozen condensate), E9 219 will recur quickly. Don't keep resetting — repeated overheating risks heat exchanger damage. Book an engineer.

• • Check the pressure gauge — if it's below 0.6 bar, low pressure can contribute to poor circulation. Repressurise to 1.2 bar, then try one reset.
• • Check the condensate pipe outside for freezing in cold weather — thaw gently if frozen, then reset. A frozen condensate is a common E9 219 cause in winter.
• • Listen for the pump — when the boiler tries to fire, you should hear the pump run. If it's silent or humming loudly, the pump may be seized and needs an engineer.
• • If E9 219 recurs after one reset, stop resetting — repeated overheating risks damage. Book a Gas Safe engineer.

The pump and heat exchanger sit inside the boiler casing. Replacing the pump, descaling the heat exchanger, or any work inside the casing is gas/electrical work that must be done by a Gas Safe Registered engineer. Don't keep resetting an overheating boiler.

• • Test the pump — confirm it's running freely and circulating properly.
• • Check for airlocks and vent the system.
• • Inspect the heat exchanger for scale, sludge or blockage.
• • Check the condensate route and flue for blockages.
• • Inspect the magnetic filter and system flow.
• • Replace the pump or clean the heat exchanger as needed, then re-commission.

Our Gas Safe Registered (594547) engineers repair every Worcester Bosch model — Greenstar CDi, Si, Ri and 8000 — across Surrey, Berkshire, Buckinghamshire and West London, and carry common sensors, fans and ignition parts on the van. Most Worcester Bosch fault-code repairs are completed in a single visit, with any part quoted and agreed before fitting.