Overview
E28 on a Baxi Platinum indicates the boiler has detected a problem related to the flue/venting or the temperature sensing and air-pressure systems that monitor safe combustion. Common causes reported by Baxi and service guides are a faulty flue NTC (flue thermistor) or its wiring, a fault with the air pressure switch or its tubing/wiring, or a physical obstruction in the flue or the condensate drain. In cold weather a frozen condensate pipe is a frequent trigger for E28 because a blocked condensate drain will cause the boiler to shut down for safety. Severity ranges from low (a frozen condensate discharge outside) to high (a blocked flue or failed safety device). Any fault that impairs the flue or air-pressure system is treated as safety-critical because it can prevent safe removal of combustion gases. Homeowners can perform a few safe checks and basic thawing/clearing steps themselves, but diagnostics and repairs involving gas, internal wiring, sensors, the fan, or the PCB must be carried out by a Gas Safe registered engineer. If you smell gas or your carbon monoxide alarm activates, treat it as an emergency: leave the property and call the emergency services and your gas emergency number immediately.
Possible Cause: Error with the NTC (Negative Temperature Coefficient) flue, air pressure switch or blocked flue or condensate
Troubleshooting Steps
Safety first
1) If you smell gas or a carbon-monoxide alarm sounds, evacuate everyone, do not use electrical switches, and call emergency services and the gas emergency number. Do not attempt any repairs.
2) Before touching the boiler or condensate pipe, switch the boiler off at the control panel and isolate the electricity at the fused spur or wall switch if it is safe to do so. Do not attempt internal electrical or gas work.
Initial visual checks (what a homeowner can safely do)
1) Confirm the display shows E28. Note whether the code is steady or intermittent and any other lights or codes.
2) Check the external condensate pipe (usually a small white plastic pipe running to an outside drain or gully). Look for frost, ice or a solid blockage on the outside of the pipe.
3) Inspect the outside flue terminal (the short round/rectangular outlet on the outside wall). Look for leaves, nests, snow or other debris partly blocking the terminal. Do not insert objects deep into the terminal; only remove visible light debris by hand or with gloved fingers.
4) Check boiler water pressure on the display. E28 is not normally a low-pressure code, but very low pressure can cause other faults — only top up pressure if you are familiar with your boiler manual.
Thawing a frozen condensate pipe (safe DIY steps)
1) With the boiler and electrical supply turned off, warm the frozen section of condensate pipe using warm water (not boiling), a warm towel, or a hairdryer on a low/medium setting. Do not pour boiling water and avoid high heat that will crack plastic pipework.
2) Work slowly from the boiler end toward the outside to encourage drainage toward the external outlet. If the frozen section is under a floor or in a cavity you cannot access safely, stop and call an engineer.
3) Once thawed, restore power and follow the boiler’s reset procedure (consult the user manual). Watch the boiler for several minutes to see if it returns to normal operation and the E28 clears.
Other homeowner checks
1) If the external flue was blocked by debris or snow and you cleared it, reset the boiler and monitor. Do not climb onto roofs or attempt risky access; use a stable ladder and someone to assist if external checks are needed.
2) If clearing the condensate or flue temporarily clears the code but E28 returns, or the boiler locks out repeatedly, stop further DIY attempts.
When to call a professional (Gas Safe engineer)
1) Call a Gas Safe registered engineer if:
- The E28 remains after thawing and resetting, or returns repeatedly.
- You see or suspect internal component faults (air pressure switch, flue NTC/thermistor, fan, wiring, PCB) or there are additional fault codes.
- You cannot safely access or clear the frozen/blocked section (under floors, inside cavities) or if the flue terminal appears damaged.
2) The engineer will perform safe pressure, flue and sensor tests, inspect and replace a failed flue thermistor, test/replace the air pressure switch or fan, clear internal condensate traps, and check wiring and the PCB as necessary. They can also advise on permanent fixes such as insulating or re-routing the condensate pipe, or installing trace heating if freezing is recurring.
Preventive steps you can ask about or do after repair
1) Insulate and, where practical, reroute exposed condensate pipework so it is less likely to freeze. Small sections can be lagged with foam insulation; prolonged or repeating freeze problems may need an engineer-installed heating trace or different routing.
2) Keep the flue terminal clear of vegetation and debris, and arrange annual boiler servicing so sensors and safety devices are checked.
Important reminders
1) Do not attempt to replace sensors, switches, fan, or any gas-carrying components yourself. Those are gas-safe tasks and must be done by a Gas Safe registered engineer. 2) Always have your boiler model, serial number and the exact error code ready for the engineer; take photos of the external condensate pipe and flue terminal if useful. 3) No cost estimates are provided here; ask the engineer for a written quote before authorising any repairs.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi Platinum.