This fault can involve incomplete combustion and carbon monoxide.
If anyone in the property feels sick, dizzy or drowsy, or you can smell gas: open the windows, leave the building, and do not switch anything on or off. Then call the National Gas Emergency Service.
0800 111 999Potterton E28 fault codewhat it means and how to fix it
Three meanings on Potterton: incorrect PCB fitted (Gold Combi HE 2007), flue NTC fault (2008–2014 and all digital displays), or flue NTC, air pressure switch, blocked flue or condensate (2015–2019 combis).
Take care
Which Potterton and which year?
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.
Gold Combi HE, 2007–2009
"Incorrect PCB Fitted". A board-configuration fault.
Engineer; usually follows board work.
Promax or Gold HE Plus / HE A, Titanium 2012, Heatmax, or any Assure / Promax Ultra
Flue temperature sensor or its lead.
Engineer; note the code as the user guide says.
Promax Combi 2015+, Titanium 2015+, Promax System 2016+, Gold Combi/System 2016+
Sensor, switch, blocked flue or blocked condensate.
Check the condensate pipe in frost; otherwise engineer, and mention the flue.
What E28 means
No other Potterton code has changed meaning as often, and the year of the boiler decides which one you have. The 2007 Gold Combi HE installation instructions list E28 as "Incorrect PCB Fitted" — a board check, nothing to do with the flue. From the 2008 Promax Combi HE Plus through the 2010–2014 HE A ranges and the 2012 Titanium it is "Flue NTC Fault", the flue temperature sensor open or short circuit, in the group the user guide says to "make a note of ... and contact your installer or service engineer".
Then the 2015 Promax Combi, 2015 Titanium Combi, 2016 Promax System and 2016–17 Gold Combi and System gained an air pressure switch, and the row became "Flue NTC Fault, Air Pressure Switch Fault, Blocked Flue, Blocked Condensate or Wiring Fault", with a new sentence in the user guide: "E28 may also indicate a blocked flue or condensate drain."
The installation manuals for those ranges add a test — apply light suction to the switch's negative spigot and "Error Code E28 should display whilst suction is applied" — and the fault-finding section E now ends with "Flue blocked or damaged: Unblock or repair flue. Condensate trap or pipework blocked: Unblock." The Assure and Promax Ultra dropped the switch again; their 28 is "Flue NTC fault" only, with a spanner and no reset. For the owner of a 2015-or-later rotary-switch combi, E28 in freezing weather is worth a look at the condensate pipe before anyone is called. For everyone else it is a sensor or a board and an engineer's visit.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Flue NTC sensor or its lead (all ranges from 2008) | Section E of the chart: cold resistance about 20 kΩ at 25 °C for the flue sensor, falling as it warms; out of range, replace it. The connector at the sensor is the first thing to reseat. | Common |
| Condensate pipe blocked or frozen (2015–2019 combis) | Back-pressure in the flue operates the air pressure switch. External condensate runs in cold weather are the usual reason; the user guide names "a blocked flue or condensate drain" for E28. | Common |
| Air pressure switch or its tube (2015–2019 combis) | The switch reads the negative pressure at the venturi through a small tube. A split tube, a switch stuck open, or the wiring between it and the board give E28 with a clear flue. | Occasional |
| Flue blocked, damaged or recirculating (2015–2019 combis) | The reason the switch exists. Debris at the terminal, a crushed flue, or a seal failure. This is a combustion safety fault and the boiler is right to stop. | Occasional |
| Wrong or unconfigured PCB (Gold Combi HE 2007) | The 2007 table's only meaning. Seen after a board replacement with the wrong part or an unset output. | Rare |
What to try yourself
Find the year and range on the data badge or the user guide. If it is a 2015-or-later Promax Combi, Titanium Combi, Promax System or Gold with the rotary knob, continue; otherwise E28 is a sensor or board fault and the user guide's instruction is to note it and call.
In cold weather, check any external condensate pipe for ice and thaw it with warm water. Check the flue terminal outside is not obstructed by leaves, a nest or snow.
Potterton offer no reset for E28. Switch the boiler off at the spur for a minute and back on; if the flue or condensate was the cause it will run. If E28 returns, contact your installer or Baxi Customer Support and say which range you have.
A blocked or damaged flue is a carbon monoxide risk. Do not try to clear anything but a frozen condensate pipe, and make sure there is a working CO alarm in the room.
Get a Gas Safe registered engineer to look at your Potterton 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.
What it costs to fix
Typical repair cost
£0–£300
Time on site
15 minutes
Free if a frozen condensate pipe was the cause. Flue NTC £70–£130 fitted. Air pressure switch £90–£160. Condensate re-route £120–£250. Flue repair varies.
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
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Related Potterton fault codes
- E160Get it checkedFan or fan wiring fault on every Potterton code display: the fan did not start or reach speed. A component fault in the user guide's words — note it and call; no reset is offered.Related: fan and flue
- E119Get it checkedThe sealed system on a rotary-switch Potterton — Promax, Titanium, Gold, Heatmax — has dropped below half a bar. The window shows E1 and then 19. Fill to 1–1.5 bar and it clears itself.Related: same brand
- E133Get it checkedGas supply interrupted, ignition failed or no flame detected — every Potterton generation. Confirm the gas supply, one reset (5 s on the knob, 1–3 s on the button), and call if it returns.Related: same brand
- E118Get it checkedThe digital-display Pottertons — Assure Combi, Assure System, Promax Ultra — have dropped below half a bar on the heating circuit. Repressurise to 1–1.5 bar and the boiler restarts on its own.Related: same brand
- E110Get it checkedSafety thermostat operated — the primary water overheated — on every Potterton code display. One reset is permitted (5 s knob or 1–3 s button); a second E110 is a circulation fault for an engineer.Related: same brand
- E125Get it checkedCirculation fault (primary circuit) on every Potterton code display — the water did not warm as expected after lighting, or overshot twice. Pump, air or sludge; an engineer job after one reset.Related: same brand
Own a Potterton 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
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.