Boiler
E28
The E28 error code on a Worcester Bosch boiler indicates a fault with the internal communication between the boiler’s control board and its components — it’s a fault that almost always requires a Gas Safe registered engineer and should not be ignored.
What does this error mean?
The E28 code signals an internal data bus or communication fault within the boiler’s electronics, meaning the main printed circuit board (PCB) is failing to communicate correctly with one or more connected components or modules. Worcester Bosch boilers use a BUS communication system to link the PCB with components such as the display unit, sensors, and external controls — when this signal breaks down, the boiler locks out for safety. This is not a fault you can resolve by topping up the pressure or bleeding a radiator; it points to an electronic or wiring issue inside the unit.
Est. repair cost
£300–£600 for PCB replacement (parts + Gas Safe labour); £60–£100 call-out and diagnosis fee alone
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Reset the boiler: Press and hold the reset button (usually marked with a flame and a line through it) for 3–5 seconds. Wait 2 minutes and see if the boiler fires up normally. This clears temporary electronic glitches.
Step 2 — Check the power supply: Switch the boiler off at the mains, wait 30 seconds, and switch it back on. A full power cycle can sometimes clear a spurious E28 fault.
Step 3 — Check any external controls: If you have recently installed or changed a smart thermostat or programmer, disconnect it and revert to a simple room thermostat or wired link to rule out an external BUS communication conflict.
Step 4 — Check for obvious signs of damp: Look around the boiler casing for any water drips, staining, or condensation that could suggest water is getting into the unit. Do not open the casing yourself — report this to an engineer.
Step 5 — If the fault persists after steps 1–4, stop. Do not attempt to open the boiler casing, touch internal wiring, or replace the PCB yourself. This is gas appliance work and must be carried out by a Gas Safe registered engineer.
📞 When to call a professional
If a reset and power cycle do not clear the E28 code, call a Gas Safe registered engineer — do not delay, as a locked-out boiler in winter can cause pipes to freeze. Tell the engineer you have an E28 fault code and describe any recent changes to your controls or any visible damp near the unit. PCB diagnosis and replacement is not DIY-safe on a gas appliance under any circumstances.
⚖️ Repair or replace?
A PCB replacement on a Worcester Bosch boiler typically costs £300–£600 including parts and labour from a Gas Safe engineer — Worcester Bosch parts are mid-to-premium priced but are widely available. If your boiler is over 10 years old, weigh this repair cost against a new A-rated boiler (typically £2,000–£3,000 installed), as an ageing boiler is likely to develop further faults. For boilers under 8 years old still under warranty or on a Worcester Bosch care plan, contact Worcester Bosch directly on 0330 123 9339 before paying for any repairs.