Boiler
E2
The E2 error code on a Worcester Bosch boiler indicates a flow temperature sensor fault — specifically that the boiler is detecting abnormally high water temperatures. This is a safety-critical fault that will lock out your boiler until it is resolved.
What does this error mean?
Your Worcester Bosch boiler continuously monitors the temperature of water flowing through the heat exchanger. When the E2 code appears, the boiler’s control board has detected that the flow temperature has exceeded safe limits — typically above 95°C — or that the sensor responsible for measuring it is sending a faulty reading. As a safety response, the boiler shuts down to prevent overheating, damage to components, or a dangerous pressure event.
Est. repair cost
£150–£300 for NTC sensor repair; £200–£400 for pump replacement; up to £600 for heat exchanger issues — all require a Gas Safe engineer
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Reset the boiler: Press and hold the reset button (usually marked with a flame/reset symbol) for 3–5 seconds. If the boiler fires up and runs normally, monitor it closely for recurrence.
Step 2 — Check the system pressure: Look at the pressure gauge on the boiler fascia. It should read between 1–1.5 bar when cold. If it is below 1 bar, top up via the filling loop until it reaches 1.2 bar, then reset again.
Step 3 — Bleed your radiators: If pressure was low or radiators have cold spots, bleed each radiator using a radiator key to release trapped air. Re-check pressure afterwards and top up if needed.
Step 4 — Check all radiator valves are open: Walk through your home and ensure every thermostatic radiator valve (TRV) and lockshield valve is fully open. Restricted flow can cause the boiler to overheat.
Step 5 — If the E2 code returns after a successful reset, do not attempt further DIY. This points to a component fault — NTC sensor, pump, or heat exchanger — that requires a Gas Safe registered engineer to diagnose safely.
📞 When to call a professional
If the E2 error returns after resetting and checking pressure and radiator valves, stop and call a Gas Safe registered engineer immediately — do not keep resetting the boiler repeatedly. Tell the engineer: ‘My Worcester Bosch boiler is showing an E2 fault code, which I understand relates to a flow temperature sensor or overheating issue.’ A qualified engineer can test the NTC sensor, check pump performance, and inspect the heat exchanger safely.
⚖️ Repair or replace?
An NTC sensor replacement typically costs £150–£300 including parts and labour from a Gas Safe engineer. A pump replacement runs £200–£400, and heat exchanger descaling or replacement can reach £300–£600+. If your Worcester Bosch boiler is under 10 years old and otherwise reliable, repair is almost always worthwhile. Beyond 12–15 years, especially if other faults have appeared, replacing with a modern A-rated condensing boiler (£2,000–£3,500 installed) is likely the more cost-effective long-term decision.