Common problems guide

The most common Pro ProCombi 100HE problems

The faults most likely to send a Pro ProCombi 100HE into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
9 documented codes
6 most common
2 DIY-safe checks
4 engineer needed

The 6 most common faults

01
RED LED BLINKS High DIY-safe

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

What to try first

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

Est. cost
£0-120
Parts
Main Control Board (PCB), Wiring harness
Full guide for RED LED BLINKS
02
RED LED LIGHT High DIY-safe

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

What to try first

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

Est. cost
£180-450
Parts
Printed Circuit Board (PCB), Ignition Electrode, Gas Valve
Full guide for RED LED LIGHT
03
GREEN LED BLINKS High Engineer

Your boiler has power but isn't starting up, which usually indicates an internal electrical issue or a loose connection.

Est. cost
£120-280
Parts
Control Board (PCB), F1 Fuse, Wiring Harness
Full guide for GREEN LED BLINKS
04
YELLOW LED Solid High Engineer

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.

Est. cost
£90-160
Parts
DHW Thermistor (NTC Sensor), Wiring harness
Full guide for YELLOW LED Solid
05
RED LED ON every 0.5-secs High Engineer

Your boiler has detected a safety-related issue with its internal airflow or pressure systems and has shut down as a precaution.

Est. cost
£120-350
Parts
Fan, Air Pressure Switch, Condensate Trap
Full guide for RED LED ON every 0.5-secs
06
RED LED Solid High Engineer

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

Est. cost
£90-160
Parts
Primary NTC thermistor, Wiring harness
Full guide for RED LED Solid
Parts most often replaced

on the Pro ProCombi 100HE

Main Control Board (PCB)Wiring harnessPrinted Circuit Board (PCB)Ignition ElectrodeGas ValveControl Board (PCB)

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Pro shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 9-code list for the Pro ProCombi 100HE

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →