Boiler
E5
The E5 error code on a Baxi boiler indicates an overheating fault — the boiler has detected that its central heating flow temperature has exceeded safe limits and has shut itself down as a safety measure. This is a serious fault that should not be ignored.
What does this error mean?
Your Baxi boiler continuously monitors the temperature of the water flowing through it. When that temperature rises above a safe threshold (typically around 90–95°C), the boiler’s overheat thermostat or sensor triggers an E5 lockout and cuts the unit off. This is a built-in safety mechanism to prevent damage to internal components and, more critically, to prevent a dangerous pressure or temperature incident.
Est. repair cost
£150–£400 for pump, sensor, or flush repair; £400–£700+ for heat exchanger replacement
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Check the pressure gauge: Look at the boiler’s built-in pressure gauge. It should read between 1–1.5 bar when cold. If it is below 1 bar, repressurise via the filling loop (consult your Baxi manual for your specific model). Low pressure alone can trigger E5.
Step 2 — Reset the boiler: Once pressure is correct, press and hold the reset button (typically marked with a flame or ‘R’ symbol) for 3–5 seconds. If the boiler fires up and runs normally, monitor it over the next 24–48 hours.
Step 3 — Check all radiator valves are open: Walk around your home and ensure every thermostatic radiator valve (TRV) and lockshield valve is fully open. Closed valves restrict flow and cause overheating.
Step 4 — Bleed your radiators: Use a radiator bleed key to release any trapped air from all radiators, starting with the ground floor. Re-check boiler pressure afterwards and top up if needed.
Step 5 — Do not attempt further DIY: If the E5 code returns after a reset, this is a gas appliance fault requiring a Gas Safe registered engineer. Do not open the boiler casing, touch the pump, or attempt to bypass any safety thermostat.
📞 When to call a professional
If the E5 error returns after a reset, or if the boiler pressure is normal and valves are all open, call a Gas Safe registered engineer immediately — do not continue resetting the boiler repeatedly. Tell the engineer: ‘My Baxi boiler is showing an E5 overheating lockout fault and it returns after reset.’ They will check the pump, heat exchanger, and temperature sensors.
⚖️ Repair or replace?
Most E5 repairs — such as pump replacement, system flush, or sensor swap — cost between £150–£400 depending on parts and labour. If your Baxi boiler is over 10–12 years old and requires a heat exchanger replacement (£400–£700+), replacement with a new A-rated boiler is likely more cost-effective in the long run. For boilers under 8 years old in otherwise good condition, repair is almost always the right call.