Pro ProCombi 100HE Fault codes & diagnostics

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

Combi Natural Gas 29.3 kW 2006 onwards Discontinued

Replaced by: ProCombi Exclusive

Download the Pro ProCombi 100HE manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
6 High 1 Low
Just want the most common Pro ProCombi 100HE faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 7 documented codes

Tap any card for details

LED / flash-pattern codes
RED LED BLINKS

Your boiler has stopped working because the internal computer has detected a general error and needs to be restarted.

High DIY-safe £0-120

What to check first

  1. Locate the reset button or dial on the front control panel.
  2. Press and hold the reset button for at least 5 seconds, then release.
  3. Wait up to 10 minutes for the boiler to complete its restart sequence.

Parts commonly replaced

  • Main Control Board (PCB)
  • Wiring harness

Related codes

Full explanation for RED LED BLINKS
Digital codes
GREEN LED ON every 0.5-secs

Your boiler has paused because it has detected a minor temporary issue, likely linked to low water pressure or a small internal communication hiccup.

Low DIY-safe £0-120

What to check first

  1. Check the pressure gauge on the front of the boiler; if it is below 1.0 bar, top it up using the filling loop.
  2. Turn the boiler off and back on at the fused spur switch to clear the temporary error.
  3. Ensure all radiator valves are open and that there are no obvious leaks around the unit.

Parts commonly replaced

  • Air Pressure Switch
  • Water Pressure Sensor

Related codes

Full explanation for GREEN LED ON every 0.5-secs
RED LED LIGHT

Your boiler has entered a safety lockout mode, meaning it has stopped working completely to protect the internal components.

High DIY-safe £180-450

What to check first

  1. Locate the reset button or selector dial on the front control panel.
  2. Press and hold the reset button (or turn the dial to 'R') for 5 seconds.
  3. Wait for the boiler to attempt to restart; if the red light returns, do not attempt further resets.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Ignition Electrode
  • Gas Valve

Related codes

Full explanation for RED LED LIGHT
RED LED Solid

Your boiler's main temperature sensor has failed or become disconnected, preventing the system from heating up as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Primary NTC thermistor
  • Wiring harness

Related codes

Full explanation for RED LED Solid
YELLOW LED Solid

Your boiler has detected a problem with the temperature sensor that controls your hot water, meaning you likely have no hot water or the temperature is inconsistent.

High Engineer only £90-160

Parts commonly replaced

  • DHW Thermistor (NTC Sensor)
  • Wiring harness

Related codes

Full explanation for YELLOW LED Solid
Status & diagnostic codes

5 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

GREEN LED Flashing 8-times a second Status Your boiler is operating in a special automatic mode to adjust its efficiency and does not actually have a fault. GREEN LED ON every 6-secs Status Your boiler is working correctly and is simply in standby mode waiting for you to turn on the heating or hot water. GREEN LED Solid Status Your boiler is operating normally and is currently busy providing heat for your radiators or hot water for your taps. YELLOW LED LIGHT Diagnostic Your boiler is currently running in a professional testing mode used by engineers to check emissions, which is why the yellow light is showing. YELLOW LED ON every 0.5-secs Diagnostic Your boiler is currently running in a special test mode used by engineers to check combustion levels, which means it is not in its normal operating state.