Error E28

Safety precautions:

- If you smell gas or suspect a leak, evacuate the property immediately and call the emergency gas number. Do not try to operate the boiler.

- Before touching or working near the boiler controls, switch the boiler off at the control panel and turn off the electrical supply at the isolator or wall switch.

- Do not open the boiler casing or attempt internal repairs unless you are a Gas Safe registered engineer. Do not bridge or bypass any safety switches (for example the air pressure switch) — this is dangerous and illegal for unqualified people.

- Use warm (not boiling) water, a hairdryer on a low safe setting, or a hot water bottle to thaw frozen condensate pipes. Do not use open flames or high temperature heat sources that could damage plastic pipework.

Initial homeowner checks you can do safely:

1. Confirm the exact fault code and note when it appeared. Take a photo of the display if possible.

2. Check the external flue terminal (outside the property): look for obvious obstructions such as leaves, bird nests, snow or ice. Remove light debris that is safe to reach; do not crawl onto roofs or access unsafe areas.

3. Locate the condensate pipe (usually a white plastic pipe running from the boiler to an external drain or gully). In cold weather, check for signs of freezing: visible ice or frost on the pipe, or dripping water stopped.

4. Check for visible water leaks or pooling around the condensate trap and boiler base. Note any slow drainage from sinks that might indicate wider drain blockage.

Specific diagnostic and safe fix steps for common causes:

A. If the condensate pipe appears frozen externally:

- Turn the boiler off and isolate electrical supply before working near the boiler outlet.

- Apply warm water (use a watering can or jug) along the frozen section, or wrap with a warm water bottle or warm towels. A hairdryer can be used on a low setting if the pipe is accessible and safe to reach. Do NOT use boiling water or open flame.

- When thawed, check that condensate water drains away freely.

- Restore power to the boiler and attempt a reset (use the boiler’s reset button or selector procedure as per your model manual). If the boiler fires and operates normally, monitor for reoccurrence and consider insulating the condensate pipe or fitting a trace heater if freezing is frequent (installation of trace heaters must be done by a professional).

B. If the condensate pipe is not frozen but the boiler shows E28 and you suspect a blocked condensate trap or backed-up condensate:

- Turn off and isolate power before inspecting near the boiler.

- If you are comfortable with basic external access (and after isolating power), you may be able to inspect and empty an external condensate trap or clear a visible blockage in the external run. Do not remove internal boiler components or drain internal condensate without training.

- If you cannot safely access the trap or the blockage appears internal, stop and call a Gas Safe engineer. A blocked condensate system can allow water to reach and prevent the air pressure switch from operating; an engineer will clear and test the condensate path and APS.

C. If the flue terminal is blocked or the flue thermistor/air pressure switch wiring is suspected:

- A simple visual clear of the external flue terminal may be done if safely reachable. Do not attempt internal checks of the flue thermistor, pressure switch or PCB connections yourself.

- If clearing the external terminal and condensate thawing/reset do not clear the fault, a trained engineer will need to test continuity of the flue thermistor, test the air pressure switch operation, check X401/PCB connections and verify fan operation and internal flue path.

Reset procedure (safe to try after thawing/clearing external blockages):

- Turn the boiler back on at the isolator and use the model’s reset button or selector switch (hold on R for about 5 seconds on models with that control) to attempt a restart. If the red lockout light is shown, hold reset as instructed in your manual.

When to call a professional:

- Call a Gas Safe registered engineer if the fault persists after you have safely checked and thawed the condensate pipe, cleared any accessible external flue obstructions and attempted a reset.

- Also call a professional if there is any sign of internal condensate backup, water inside the boiler casing, repeated lockouts, suspected wiring/sensor faults, fan or air pressure switch failures, or if you are unsure or uncomfortable performing the safe checks above.

- Do not attempt internal repairs, sensor replacements, or bypassing the air pressure switch. A qualified engineer will carry out the correct electrical and component tests, replace failed parts and perform mandatory safety checks.

Additional practical tips:

- Photograph the fault code and any visible issues for the engineer to review before arrival.

- Note if household drains have been slow recently — this can indicate an external drain blockage that affected the boiler condensate outlet.

- To reduce recurrence in cold weather, insulating external condensate pipes or routing them in a warmer path can help; installation of pipe trace heating must be done by a professional.

If none of the above clears E28, arrange a visit by a Gas Safe registered engineer. They have the training and tools to safely diagnose flue thermistors, the air pressure switch, PCB/wiring, fans and internal condensate traps and complete the necessary repairs.