Baxi E28 Fault Code
The E28 fault means the boiler's flow sensor cannot detect water circulating through the system. Most commonly a pump failure or airlock — but limescale on the heat exchanger is the underlying driver in hard water areas.
What is the Baxi E28 fault code?
The Baxi E28 fault is triggered when the PCB detects insufficient water flow through the primary circuit. The boiler's flow sensor (or differential pressure sensor depending on model) monitors water movement during each heating cycle. If circulation is not detected within the expected time, E28 locks out the boiler to prevent heat exchanger damage from running dry or overheating on stagnant water.
What causes the E28 fault?
The pump impeller seizes from corrosion or extended idle periods. Common on Baxi boilers in South London properties where hard water accelerates corrosion inside the pump casing.
Air trapped inside the pump prevents the impeller from generating flow. The pump motor runs but no water moves — E28 follows within seconds.
Heavy magnetite sludge in the primary circuit restricts flow to the point the pump cannot generate the flow rate the sensor expects.
The flow sensor itself can fail, showing E28 even when the pump and circuit are functioning correctly. Diagnosed by confirming circulation with a pressure gauge.
In South London's hard water, limescale builds inside the heat exchanger over years, narrowing the water path. Even a working pump cannot push enough flow through a heavily scaled exchanger.
A stuck diverter valve can block water from entering the heating circuit, causing E28 when the boiler attempts to run the central heating.
What you can safely check yourself
Low pressure can cause poor pump output. Check the gauge — if below 1 bar, repressurise to 1.2 bar via the filling loop before resetting.
After resetting, place your hand on the boiler casing near the pump. A hum or faint vibration means the motor is turning. Silence suggests a seized impeller.
Air in the system can cause flow sensor misreadings. Bleed radiators, repressurise to 1.2 bar, and attempt one reset.
Do not reset the boiler more than once if the fault code returns immediately. Repeated resets without diagnosis can mask a worsening fault.
What needs a Gas Safe engineer
- Test pump speed and current draw with a multimeter
- Manually free a seized pump impeller if possible
- Bleed air from pump if airlock is suspected
- Test flow sensor output and replace if faulty
- Power flush the system if sludge is restricting the circuit
- Check and free any stuck diverter valve on combi models
- Replace pump if seized or output is below specification
Seized pumps are disproportionately common across South London — Wandsworth, Merton, Lewisham, Lambeth, Southwark, Greenwich, and Bromley — where hard water corrosion inside the pump casing and sludge-heavy systems create the conditions for impeller seizure. Annual servicing with a magnetic filter check catches pump degradation before it results in an E28 lockout.
How much does a E28 repair cost?
Costs below are UK averages. Reion provides a fixed quote after the £80 diagnostic visit — no obligation to proceed.
How to reset a Baxi boiler showing E28
Check system pressure and repressurise to 1.2 bar if below 1 bar.
Bleed any cold radiators, then repressurise again.
Hold the reset button for 3 seconds.
Listen for pump operation within 10 seconds of reset.
If E28 returns, call a Gas Safe engineer.
Pump replacement on Baxi boilers typically costs £280–£420 all in. On a boiler under 12 years old with no other faults, it is worth doing rather than replacing the boiler.
Common questions about the Baxi E28 fault
What does a Baxi E28 fault code mean?
Can I fix a Baxi E28 fault myself?
Why is E28 common on older Baxi boilers in London?
How much does a Baxi E28 repair cost in London?
How do I prevent Baxi E28 faults recurring?
Other Baxi fault codes
Need a Baxi engineer in London?
Reion is Gas Safe registered (919881), based in South London, and available 24/7. Fixed price after the diagnostic visit — no hidden charges.
