A plain E28 code on the Baxi boiler families listed in the manufacturer’s current UK table means a flue NTC temperature-sensor circuit fault: short circuit or open circuit. Baxi also says E28 can appear when an external condensate pipe freezes on some boilers, so the exact model, weather and symptoms matter.
Do not confuse plain E28 with A.00.28 on newer Combi 2 and System 2 ranges. Baxi defines A.00.28 as a solar temperature sensor that has been removed or is reading below range. Photograph the punctuation and identify the boiler before following any advice.
What plain Baxi E28 means
Baxi’s official error-code table groups plain E28 with products including the Platinum Compact, Duo-tec Compact, Megaflo Compact System, Main Eco Compact, earlier 600 and 800 Combi/System, Duo-tec, Assure, Platinum, Platinum+, Megaflo and EcoBlue ranges. In that group, E28 is “Flue NTC sensor fault — short circuit/open circuit”.
An NTC sensor changes electrical resistance with temperature. The boiler control uses the signal to interpret temperature. The code indicates that the flue-temperature sensor circuit is not providing the expected electrical reading. It does not establish from the display alone whether the sensor, connector, wiring or control board is responsible.
Why Baxi also mentions frozen condensate
Baxi’s homeowner cold-weather guidance says that a frozen external condensate pipe may cause E133 or E28 on most Baxi boilers. A blocked condensate route can make the boiler shut down to protect itself. This is a separate practical context from the code-table sensor description.
The two official statements are why model and circumstances are essential. If E28 appears during freezing weather and the boiler has an external plastic condensate pipe, check for the visible signs Baxi describes. If it appears in mild weather or returns after a safely cleared freeze, arrange diagnosis of the code rather than assuming ice.
E28 is not A.00.28
Current Baxi Combi 2 and System 2 models use longer dotted codes. Baxi’s table lists:
- E28: plain code on the listed “other” group—flue NTC sensor open/short circuit;
- A.00.28: on listed Combi 2/System 2 products—solar temperature sensor removed or below range;
- E.00.20: a separate newer code—flue-gas temperature sensor disconnected or below range; and
- E.00.21: flue-gas temperature sensor short-circuited or above range.
These examples show why dropping dots or zeros changes the meaning. State the complete code when booking a repair.
Safe first checks
- Photograph the full display and any alternating code.
- Identify the exact Baxi model from the fascia, user guide, warranty certificate or Benchmark record.
- Note the outdoor temperature and whether the fault began during a freeze.
- From ground level, identify whether a plastic condensate pipe runs outside; do not climb or dismantle boxing.
- Listen for unusual gurgling without removing the boiler case.
- Record whether heating, hot water or both have stopped.
- Follow only the exact model’s user instructions for one reset.
Do not top up pressure, bleed radiators or buy a temperature sensor merely because E28 is displayed. None of those actions confirms the cause.
How to recognise a potentially frozen condensate pipe
The condensate pipe is usually plastic and carries water produced by a condensing boiler to a drain. A section routed outdoors can freeze at an exposed end, bend or sag during prolonged sub-zero weather. Possible clues include:
- the fault started during a hard frost;
- the boiler was operating normally before the temperature fell;
- an accessible external plastic condensate pipe has visible ice;
- the boiler or pipework makes gurgling sounds; and
- nearby homes have experienced frozen condensate problems.
These clues are not proof. Do not confuse the white plastic condensate pipe with the metal flue, pressure-relief discharge or another waste pipe.
What Baxi says homeowners can do about a frozen pipe
Baxi advises switching the boiler off at its control panel and isolating its electrical supply before gently warming the exposed frozen section. It recommends a hot-water bottle, microwaveable heat pack, warm damp cloth or warm—not boiling—water from a watering can.
Take care outdoors: spilled water can refreeze and create a slip hazard. Work only from a safe standing position. Do not use a naked flame, heat gun, boiling kettle, hammer or sharp object. Do not climb a ladder to reach high pipework.
After the blockage has thawed, restore power and follow the exact operating instructions to restart the boiler. If it does not work, or E28 returns, call a Gas Safe registered engineer.
When not to attempt thawing
Do not attempt it if you cannot positively identify the condensate pipe, the pipe is high or inaccessible, the ground is unsafe, the pipe is damaged, water is leaking near electrics or the weather makes the task hazardous. Arrange professional help.
If the code appeared outside freezing conditions, skip the thawing idea and obtain a model-specific diagnosis. Warming random pipes is not troubleshooting.
Can I reset Baxi E28?
Baxi boilers use different reset controls. Some have a dedicated button; others use a selector switch or thermostat knob. Consult the exact user guide and try one reset only if the manual permits it—normally after any confirmed external frozen blockage has been cleared.
A reset cannot repair an open or short sensor circuit. Baxi says repeated lockout indicates a fault requiring an installer or service engineer. Stop if E28 immediately returns.
Why a flue-sensor fault needs an engineer
The sensor, its connections and related boiler components are inside the appliance. Diagnosis may require removal of a functional case, electrical measurements and checks against Baxi service data. It is not safe to reach the part from a fault-code description.
Gas Safe Register explains that a boiler case secured with screws often forms part of the combustion circuit. Consumers should not remove it. Never unplug, bridge or replace a flue temperature sensor yourself.
What an engineer may need to establish
Without prescribing a repair, the engineer will confirm the appliance and code family, inspect the relevant sensor circuit and connections, compare readings with the manufacturer’s information, assess condensate routing where relevant and verify safe operation after the fault is corrected.
The display does not prove that a new sensor alone will solve the problem. Wiring, connections or controls may need testing, and a winter condensate obstruction may be part of the history.
Is E28 a gas-supply fault?
Baxi does not define plain E28 as a gas-supply fault in its current common-code table. Other codes, such as E133 on relevant models, are associated with ignition or gas-supply problems. Do not check the gas valve or internal gas components.
If you smell gas, a carbon monoxide alarm sounds or anyone becomes unwell, treat that as an emergency regardless of the display. Avoid flames and electrical switches, leave the affected area and follow official gas-emergency guidance.
Is E28 caused by low pressure?
Not according to Baxi’s plain E28 definition. Relevant Baxi families use other codes for low system pressure. You can record the normal user-visible gauge reading, but do not repeatedly refill the boiler to chase E28.
How to prevent another condensate freeze
If an engineer confirms that the condensate froze, ask them to assess the pipe route against current manufacturer guidance. Baxi suggests professional measures such as rerouting more of the pipe internally, using suitable diameter, weatherproof insulation or an appropriate trace-heating arrangement.
Do not modify the condensate pipe yourself without knowing the required fall, material, termination and boiler instructions. Poor alterations can create another blockage or leak.
What to tell the booking team
- the exact code including dots and zeros;
- the full Baxi model name;
- whether the fault coincided with sub-zero weather;
- whether an external condensate pipe was visibly frozen;
- which services stopped;
- whether one correct reset was tried; and
- whether the code returned after the weather warmed.
This information helps separate a winter external blockage from an internal sensor-circuit diagnosis and reduces the risk of a wasted visit.
Frequently asked questions
What does Baxi E28 mean?
For the plain-code product group in Baxi’s current UK table, it means a flue NTC sensor circuit open or short fault.
Can a frozen condensate pipe cause E28?
Baxi’s homeowner guidance says E28 can appear on some boilers when an external condensate pipe freezes. Model, weather and symptoms must be considered together.
Can I thaw the pipe myself?
Only if it is positively identified and safely accessible from ground level. Follow Baxi’s warm—not boiling—methods and avoid flames, tools and unsafe access.
Will a reset fix the flue sensor?
No. One manual-approved reset may clear a temporary lockout, but it cannot repair an open or short circuit.
Is A.00.28 the same code?
No. Baxi lists A.00.28 as a solar temperature-sensor issue on newer Combi 2/System 2 ranges.
Related boiler-help guides
- Baxi boiler fault codes
- How to deal with a frozen condensate pipe
- Baxi E20 fault code
- Why does my boiler reset keep failing?
Is your Baxi boiler still showing E28?
If safe external frost checks do not clear the fault, book a fixed-price Incredaboil repair for a model-specific sensor and boiler diagnosis.