Potterton E13 Fault Code: Causes, Fixes & Repair Costs
What does the Potterton E13 fault code mean?
The E13 code on a Potterton boiler indicates a flue gas or combustion safety fault. The boiler's control system has detected an abnormality in the combustion or flue gas pathway and has shut itself down as a precaution to protect occupants and the appliance. It is a safety lockout, meaning the boiler will not restart until the underlying problem is resolved. Note that E13 is a distinct code from E133 — E133 specifically relates to ignition lockout or gas supply interruption, while E13 sits earlier in Potterton's fault numbering and relates more broadly to flue gas or combustion safety conditions. E12, the preceding code, concerns a flow/return temperature differential fault. If your display shows E133, that points primarily to ignition or gas supply issues rather than the flue gas safety condition described here.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Frozen or Blocked Condensate Pipe Common
During cold spells, the water inside the condensate pipe — which carries acidic drainage from the boiler to an external drain — can freeze solid. This blockage prevents proper drainage and triggers the combustion safety lockout. It is one of the most frequent causes of E13 appearing in winter months.
- Flue Blockage or Damage Common
The flue pipe channels waste combustion gases safely out of the property. A partial or complete blockage caused by a bird's nest, accumulated debris, or ice build-up prevents gases from escaping correctly, causing the boiler's safety systems to intervene and lock the unit out.
- Faulty Fan or Air Pressure Switch Sometimes
The boiler's fan creates the draught needed to expel flue gases. A pressure switch monitors whether the fan is running correctly before combustion is allowed to begin. If the fan is failing or the air pressure switch has developed a fault, the PCB may not receive the correct signal and will raise a combustion safety fault.
- Flue Thermostat or Sensor Fault Sometimes
An overheat thermostat on the flue or a faulty flue thermistor can either trip in response to genuinely high flue temperatures or generate inaccurate readings that the control board interprets as a safety-critical condition. Either scenario results in a lockout.
- Faulty PCB Rare
The printed circuit board is the control centre of the boiler. If the PCB develops an internal fault it can misinterpret signals from sensors or fail to co-ordinate components correctly, producing spurious combustion safety codes including E13.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on the boiler's control panel — on most Potterton models it is a clearly labelled button or switch. Press and hold it for 3–5 seconds. If the boiler fires up and runs normally, monitor it over the next hour. If E13 returns, do not keep resetting; move to the next step.
- Check for a frozen condensate pipe (cold weather only) DIY safe
The condensate pipe is typically a white or grey plastic pipe, around 22 mm in diameter, that exits the boiler and runs to an external drain or soil stack. If outdoor temperatures are at or near freezing, feel along the pipe for a solid or unusually cold section. Gently pour warm — not boiling — water along the frozen section until it clears, then dry the pipe and reset the boiler. If the pipe freezes repeatedly, it should be insulated by an engineer.
- Check the external flue terminal DIY safe
From outside the property, visually inspect the flue outlet — usually a white or grey plastic cap on the wall or roof. Look for obvious obstructions such as a bird's nest, heavy debris, or ice covering the grille. Do not attempt to climb ladders or access roofs. If you suspect a blockage you cannot safely see or reach, this is a job for an engineer.
- Check system pressure DIY safe
Look at the boiler's pressure gauge. It should read between 1.0 and 1.5 bar when the system is cold. If it has dropped below 1 bar, top it up carefully via the filling loop underneath the boiler until it reaches approximately 1.2 bar, then re-attempt a reset. Low pressure alone is unlikely to cause E13 but ruling it out takes only moments.
- Do not attempt to inspect gas components, the fan, or the PCB yourself Gas Safe engineer
Internal components including the fan, air pressure switch, flue thermostat, gas valve, and PCB must only be inspected and worked on by a Gas Safe registered engineer. Opening the boiler casing to access these parts without Gas Safe registration is unsafe and may invalidate any warranty or insurance.
- Call a Gas Safe registered engineer Gas Safe engineer
If the boiler will not stay running after a reset, or E13 keeps returning, stop resetting the boiler and arrange for a Gas Safe registered engineer to visit. They will carry out a flue gas analysis with a calibrated analyser, inspect the full flue run, test the fan and air pressure switch, check the flue thermostat and sensors, and assess the PCB. Do not continue using the boiler until it has been cleared — a combustion safety lockout should always be taken seriously, and fitting a carbon monoxide alarm near the appliance is strongly recommended if you do not already have one.
Parts you may need
- Condensate pipe insulation kit · from £15
- Air pressure switch · from £45
- Flue fan (draught inducer) · from £95
- Flue overheat thermostat / safety thermostat · from £35
- Flue thermistor (NTC sensor) · from £25
- PCB (printed circuit board) · from £180
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £100–£380, depending on the underlying cause.
Frequently asked questions
What is the difference between Potterton E13 and E133?
They are two separate fault codes. E13 is a flue gas or combustion safety fault — it means the boiler has detected an issue with how combustion gases are being produced or expelled. E133, by contrast, is specifically an ignition lockout or gas supply interruption fault, meaning the boiler attempted to ignite and failed. If your display clearly shows three digits — E133 — the focus should be on gas supply, ignition electrodes, and the gas valve rather than the flue gas pathway issues described on this page.
Can I thaw the condensate pipe myself, and will that fix E13?
Yes, thawing a frozen condensate pipe is a homeowner-safe task. Gently apply warm (not boiling) water to the frozen section of the external pipe until it flows freely, then reset the boiler. If this clears the fault and the boiler runs normally, the frozen pipe was almost certainly the cause. To prevent recurrence, ask a Gas Safe engineer to insulate the exposed section of pipe — it is an inexpensive job that avoids repeat callouts every cold snap.
Is E13 dangerous — could it mean carbon monoxide is leaking?
The E13 lockout itself means the boiler has shut down to prevent unsafe combustion, so the immediate risk is reduced while the boiler is off. However, a flue fault or combustion problem is exactly the type of fault that, if ignored or repeatedly overridden, can allow carbon monoxide to accumulate. Carbon monoxide is colourless and odourless. You should fit a CO alarm near the boiler if you do not have one, and you should not run the boiler continuously resetting it until a Gas Safe engineer has confirmed it is safe.
My boiler is over 10 years old and keeps showing E13 — is it worth repairing?
It depends on what needs replacing. Inexpensive fixes such as condensate pipe insulation or a sensor swap are usually worth doing regardless of age. However, if the diagnosis points to a failed heat exchanger or PCB on a boiler that is already 12–15 years old, repair costs can reach £350–£600 or more, and a new boiler — typically £1,500–£3,000 installed — may be more cost-effective in the long run. A Gas Safe engineer can give you an honest assessment once the fault is diagnosed.