Baxi E28 fault codewhat it means and how to fix it
Flue thermistor fault — and on the Platinum ranges also the air pressure switch, a blocked flue or a blocked condensate drain. Which meaning applies depends on which Baxi you have.
Take care
Get a Gas Safe registered engineer to look at your Baxi E28
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
Which Baxi is showing E28?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
A Platinum or Platinum+, and it is freezing outside
Baxi's Platinum table names a blocked condensate drain, and in a freeze that is the first thing to check.
Follow Baxi's thawing guide for the outside section of the condensate pipe (warm, not boiling, water), then reset once with the selector. If it returns, call an engineer.
A Platinum or Platinum+ in normal weather
Flue sensor, air pressure switch, a flue obstruction or wiring. The engineer's flow tests the switch and the sensor.
Note the code and book a Gas Safe registered engineer, as the user guide says.
Any other Baxi — Duo-tec HE, 600, 800, Compact, Assure, Megaflo
The flue thermistor or its plug. A component fault with no householder reset.
Book an engineer. It is a sensor swap on most of these boilers.
What E28 means
E28 is the one code in Baxi's three-digit table whose meaning changed with the boiler. On the Duo-tec Combi HE A of 2010 and on every digital-display Baxi (Duo-tec 2, Compact, 600, 800, Assure, Megaflo) it is one thing: "Flue NTC Fault" or "Flue NTC fault", the thermistor at the flue outlet reading open or short circuit, and Baxi's professional page agrees — "Flue NTC sensor fault — short circuit/open circuit".
On the Platinum Combi, Platinum+ 40 Combi and Platinum+ 32 System the same line reads "Flue NTC Fault, Air Pressure Switch Fault, Blocked Flue, Blocked Condensate or Wiring Fault", and the manual's summary sentence is different too: "E20 & E50 indicate faulty components. E28 includes possible faulty components or blockage." The Platinum user guide repeats it for the householder: "E28 may also indicate a blocked flue or condensate drain." The reason is a piece of hardware. The Platinum family has an air pressure switch that proves the fan is moving air through the flue, and its fault-finding flow for E28 checks "Air Pressure Switch faulty. Check for continuity across terminals 1 & 2"; the Duo-tec HE and the digital-display boilers have no such switch, so on them E28 can only be the thermistor. That distinction changes the advice.
A flue-sensor E28 is a sensor swap. A Platinum E28 in a cold snap, on a boiler whose condensate pipe runs outside, is quite likely a frozen condensate drain, which Baxi's own how-to guide lets the householder thaw with warm water. Neither generation offers a householder reset for E28: the Platinum user guide puts it among the codes to note and report, and the digital-display boilers show it with the spanner symbol. Not to be confused with E130, which is the flue sensor working and reading too hot.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Flue thermistor open or short circuit | The meaning on every non-Platinum Baxi and one of the meanings on the Platinum. Baxi's test: about 20 kΩ at 25 °C, falling with temperature. The 600 and 800 flue sensor is part 7207892, a bayonet fitting turned 90° to remove. | Common |
| Blocked or frozen condensate drain (Platinum ranges) | Named in the Platinum table. Water backs up until the air pressure switch cannot prove the flue is clear. Common in a freeze when the condensate pipe runs outside; Baxi's thawing guide applies. | Common |
| Air pressure switch or its tubes (Platinum ranges) | The Platinum flow checks continuity across the switch's terminals 1 and 2 with the fan running. A split or kinked sensing tube fails the test as surely as a dead switch. | Occasional |
| Blocked flue (Platinum ranges) | Named in the Platinum table. A terminal obstructed by a nest, debris or a badly fitted extension, or a flue run that has sagged and filled with condensate. | Occasional |
| Wiring | The last item in the Platinum line and the usual intermittent cause on the others: a plug on the sensor or the switch that has corroded, or a lead chafed at the case edge. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£0–£250
Time on site
45 minutes
Thawing a condensate pipe costs nothing. Flue sensor (Baxi 7207892) fitted £90–£140. Air pressure switch on a Platinum £100–£160. Flue investigation and clearing £120–£250.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Condensate trap and siphon
COND-TRAP£15–£38Plumbing merchant
Price checked 28 September 2026
Baxi / Potterton / Main flue NTC sensor
7207892£22–£50Authorised Baxi parts distributor
Price checked 28 September 2026
Baxi Platinum / Potterton air pressure switch
£35–£80Authorised Baxi parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Baxi fault codes
- E130Stop — call an engineer"Flue NTC operated": the flue gas got too hot and the boiler shut down. Baxi allow one reset on every generation, then it is a heat exchanger or flue problem for an engineer.Related: fan and flue
- E160Stop — call an engineerFan fault on every three-digit Baxi. The boiler will not light without proof the fan is moving combustion air. No householder reset on any generation; fan, wiring or board.Related: fan and flue
- E.04.13Stop — call an engineerFan blocked or over speed on the Baxi 200/400 Combi and Combi 2. Baxi's remedy is the fan-and-PCB connection, then the air-gas unit. No householder fix; do not keep resetting.Related: fan and flue
- E.01.20Stop — call an engineer"Maximum flue gas temperature reached" on the Baxi 200/400 Combi and Combi 2. Baxi's cause is a heat exchanger blocked on the flue side; the fix is a strip and clean, not a reset.Related: fan and flue
- E133Get it checkedBaxi's ignition lockout: "the gas supply has been interrupted, ignition has failed or the flame has not been detected". Check the gas is on, reset once. If it returns, stop.Related: same brand
- E118Get it checkedLow water pressure on the digital-display Baxis: 600, 800, Duo-tec 2, Compact, Assure, Megaflo. Defined by Baxi as primary pressure under 0.5 bar. Repressurise and it clears itself.Related: same brand
Own a Baxi boiler? Save it and its codes come first next time.
Related guides
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Manufacturer support portal
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.