Heatline Sargon 28 Fault codes & diagnostics

23 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 28 kW 2006-2010 Discontinued

Replaced by: Heatline Capriz

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Severity at a glance

Each cell = one fault code. Hover to identify.
19 High 2 Medium 2 Low
Just want the most common Heatline Sargon 28 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 23 documented codes

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E01

Your boiler is unable to light the flame needed to heat your water and home, often because the gas supply is interrupted or there is a problem with the internal spark.

High DIY-safe £100-£250

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. If you have a pre-payment meter, verify that you have enough credit
  3. Reset the boiler by turning the selector knob to 'Reset' for 5 seconds and then back to the heating/hot water position

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • PCB (Control Board)

Related codes

Full explanation for E01
E02

Your boiler has switched itself off because the water inside has become too hot, usually caused by a blockage or a pump that isn't circulating water correctly.

High DIY-safe £120-300

What to check first

  1. Check that all radiator valves are fully open to ensure water can flow.
  2. Ensure the boiler pressure is between 1 and 1.5 bar on the pressure gauge.
  3. Once the boiler has cooled down, attempt to reset it by turning the dial to 'Reset' for a few seconds.

Parts commonly replaced

  • Circulation pump
  • Overheat thermostat
  • Main Heat Exchanger

Related codes

Full explanation for E02
E03

Your boiler has detected that the exhaust gases are too hot or cannot escape properly, so it has shut down for safety.

High Engineer only £120-250

Parts commonly replaced

  • Flue Gas Sensor
  • Fan
  • Heat Exchanger

Related codes

Full explanation for E03
E04

Your boiler has stopped working because the water pressure is too low, usually because the system needs top-up or there is a small leak.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath the boiler.
  2. Slowly open the valve or valves on the filling loop until you hear water entering the system.
  3. Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the valves tightly.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for E04
E05

Your boiler has detected a problem with a temperature sensor and has stopped working to prevent damage.

High Engineer only £90-160

Parts commonly replaced

  • Central heating flow NTC thermistor
  • Wiring harness connection

Related codes

Full explanation for E05
E06

Your boiler's temperature sensor for hot water has stopped working, so the system is unable to tell how hot the water is and has stopped heating it for your safety.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC Sensor
  • Sensor wiring harness

Related codes

Full explanation for E06
E10

Your boiler has lost track of the water pressure because the internal sensor is either broken or has a loose connection.

High Engineer only £120-190

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

Full explanation for E10
E11

Your boiler has stopped working because water is not moving through the system properly, which is causing the unit to get too hot too quickly.

High DIY-safe £180-350

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar on the gauge.
  2. Ensure all radiator valves are fully open to allow water to flow.
  3. Check if any radiators need bleeding to remove trapped air.

Parts commonly replaced

  • Circulation pump
  • Central heating filter
  • Main heat exchanger

Related codes

Full explanation for E11
E16

Your boiler has stopped working because the internal fan, which safely exhausts fumes, isn't spinning at the correct speed.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for E16
E22

Your boiler's internal computer brain is confused because it has lost its settings or has been programmed incorrectly.

High Engineer only £180-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Display PCB
Full explanation for E22
Showing 11–20 of 23
E25

Your boiler's main internal computer has developed a technical error and can no longer communicate with the rest of the unit.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E25
E35

Your boiler thinks a flame is present even though no gas should be flowing, which is a safety conflict that stops the system from running.

High Engineer only £120-£350

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Main PCB
Full explanation for E35
F0

Your boiler has stopped working because the water pressure inside the system is either too empty or has become overfilled.

High DIY-safe £60-140

What to check first

  1. Check the pressure gauge on the front of the boiler; it should be between 1.0 and 1.5 bar.
  2. If the pressure is below 1.0, use the filling loop valves underneath the boiler to carefully add water until the needle reaches 1.2 bar.
  3. If the pressure is above 2.5, you may need to bleed a radiator to release excess water and bring the pressure down.

Parts commonly replaced

  • External Filling Loop
  • Pressure Sensor
  • Expansion Vessel recharge

Related codes

Full explanation for F0
F1

Your boiler has shut down because it has reached an unsafe temperature and needs to cool down and be reset.

High DIY-safe £90-180

What to check first

  1. Switch off the electricity supply to the boiler and wait 15 minutes for it to cool down.
  2. Check that your radiator valves are open and that the system pressure is between 1 and 1.5 bar.
  3. Turn the boiler back on and press the 'Reset' button.

Parts commonly replaced

  • Overheat Thermostat
  • Thermal Fuse
  • Circulation Pump

Related codes

Full explanation for F1
F2

Your boiler's hot water sensor has malfunctioned, meaning the system can no longer tell how hot your water is and has stopped heating it for safety.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW NTC Temperature Sensor
  • Wiring harness

Related codes

Full explanation for F2
F3

Your boiler has stopped working because a sensor that monitors water temperature has likely broken or become faulty.

High Engineer only £90-160

Parts commonly replaced

  • NTC Temperature Sensor
  • Sensor Wiring Loom

Related codes

Full explanation for F3
F4

Your boiler has failed to light the flame or is struggling to drain away waste water, causing it to shut down for safety.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances in your home are working to ensure your gas supply is active.
  2. If it is freezing outside, check if the external white plastic condensate pipe is frozen and thaw it with warm water.
  3. Press the Reset button on the control panel to see if the boiler restarts.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Condensate Trap or Siphon
  • Spark Generator

Related codes

Full explanation for F4
F5

Your boiler has detected that a safety sensor measuring exhaust gas temperatures is broken or malfunctioning, causing the system to shut down for safety.

High Engineer only £120-220

Parts commonly replaced

  • Flue Gas NTC Sensor
  • Wiring Harness
  • Main PCB

Related codes

Full explanation for F5
F6

Your boiler's outside temperature sensor has failed or has a bad connection, which may cause your heating to behave unpredictably.

Low Engineer only £90-160

Parts commonly replaced

  • External temperature sensor
  • Sensor wiring

Related codes

Full explanation for F6
F7

Your boiler has stopped working because the internal fan that clears out exhaust gases is rotating at the wrong speed.

High Engineer only £180-350

Parts commonly replaced

  • Fan motor
  • PCB (Main circuit board)
  • Wiring harness

Related codes

Full explanation for F7
Showing 21–23 of 23
F8

Your boiler has detected that the internal fan is spinning at a time when it should be switched off, causing the system to shut down for safety.

High Engineer only £180-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Fan Assembly
  • Wiring Harness

Related codes

Full explanation for F8
F9

Your boiler has switched itself off because it has detected that the water inside is getting too hot, likely due to a circulation problem.

High DIY-safe £100-280

What to check first

  1. Check that all radiator valves are fully open
  2. Check that the boiler pressure is between 1.0 and 1.5 bar
  3. Once the boiler has cooled down, press the reset button

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Thermistor (NTC Sensor)

Related codes

Full explanation for F9
OC

Your boiler has detected an outdoor temperature sensor and has automatically turned on a feature that adjusts your heating based on the weather outside.

Low DIY-safe £0

What to check first

  1. Check if your heating is still working as expected
  2. Refer to the manual if you wish to adjust the weather compensation settings
  3. No action is required if the heating is comfortable, as this is an status indicator rather than a breakdown

Related codes

Full explanation for OC