Keston Combi 30 Fault codes & diagnostics

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

Combi Natural Gas 30 kW 2013 onwards Discontinued
GC Number 47-930-04
Download the Keston Combi 30 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
47-930-04 Combi 30 2013–present
Just want the most common Keston Combi 30 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 4 documented codes

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Flame Loss

Your boiler has started an ignition sequence but the flame has gone out, meaning the system has shut down as a safety precaution.

High DIY-safe £120-400

What to check first

  1. Check that your gas emergency control valve is open and you have credit on your meter
  2. Check if other gas appliances in your home, such as a hob, are working correctly
  3. Reset the boiler by pressing the 'Restart' button for two seconds

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve
  • Condensate Trap (if blocked)

Related codes

Full explanation for Flame Loss
Ignition Lockout

Your boiler is failing to light the gas to start the heating and hot water process, likely due to a temporary interruption in the gas supply.

High DIY-safe £80-£350

What to check first

  1. Check if other gas appliances in your home, like a hob, are working to confirm your gas supply is active.
  2. Ensure your gas meter has credit if you are on a prepay system.
  3. Press the Reset button on the boiler control panel for 2 seconds.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Spark Generator

Related codes

Full explanation for Ignition Lockout
Low water pressure

Your boiler has detected that the water pressure inside the heating system is too low to run safely, causing it to shut down temporarily.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (braided silver hose) usually found underneath the boiler.
  2. Slowly open the valves until the pressure gauge reaches between 1.0 and 1.5 bar.
  3. Close the valves tightly and bleed your radiators to remove any trapped air.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for Low water pressure
Overheat Lockout

Your boiler has switched itself off because it has reached a temperature that is too high, often caused by low water pressure or air trapped in the system.

High DIY-safe £0-180

What to check first

  1. Check the pressure gauge and refill the system to 1.0 bar if it is too low
  2. Bleed all radiators to remove trapped air and ensure all radiator valves are fully open
  3. Press the reset button on the boiler control panel

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • System Pressure Sensor

Related codes

Full explanation for Overheat Lockout