Worcester Bosch [E9 219] fault codewhat it means and how to fix it

E9 219 is a published pairing, though it took the right manual to find it. The Greenstar CDi Compact and Si Compact ErP tables list "E9 219 — safety sensor temperature too high — the main heat exchanger has overheated, maximum temperature 105 °C" as a locking error cleared with the reset button, with 277 as the blocking stage before it: the safety sensor passing 95 °C and the boiler waiting to see whether it cools. The Greenstar i ErP table does not use 219; it publishes E9 224, "flue or high limit thermostat activated (safety circuit)", and E9 276, "primary flow temperature exceeded 95 °C".

The Greenstar CDi Classic table gives E9 on its own as "safety temp. limiter in CH flow has tripped". So which number you see depends on the range, and the E9 meaning is the same across all of them: an overheat lockout.

Worcester Bosch boilers carry a safety sensor or thermal cut-out that operates when the heat exchanger exceeds its limit, and the control board latches the fault so the appliance cannot simply restart. Overheating in a modulating condensing boiler is nearly always a flow problem rather than a heat problem: the burner produces heat at a controlled rate, and if water is not moving through the exchanger quickly enough, the small volume sitting in it boils. Pump failure, a sludged system, closed valves and a scaled heat exchanger all present identically. The reason this is treated as a danger-severity fault is not fire risk but component risk — the heat exchanger is the most expensive part in the boiler and repeated overheat cycles are what crack it.