Sime Format C Combi Fault codes & diagnostics

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

Combi Natural Gas 1998-2008 Discontinued
GC Numbers 47-719-1247-719-1347-719-21
Download the Sime Format C Combi 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 →

Just want the most common Sime Format C Combi faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 5 documented codes

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LED / flash-pattern codes
Digital codes
Red LED after flow switch

Your boiler has detected that water is not circulating properly through the system, causing it to overheat and shut down for safety.

High DIY-safe £120-£350

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar
  2. Ensure all radiator valves and internal stop taps are fully open
  3. Gently bleed your radiators to remove any trapped air pockets

Parts commonly replaced

  • Circulating Pump
  • Water Flow Switch
  • Limit Thermostat

Related codes

Full explanation for Red LED after flow switch
Red LED on (solid)

Your boiler has stopped working because it couldn't successfully light the flame to provide heat or hot water.

High DIY-safe £100-280

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. If you have a prepay gas meter, ensure it has credit
  3. Turn the selector dial to the 'R' (Reset) position for a few seconds, then back to the heating or hot water setting

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve

Related codes

Full explanation for Red LED on (solid)
Status & diagnostic codes

1 operating states & engineer diagnostics

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

Orange LED on Status Your boiler is in normal standby mode and is simply waiting for a request from your thermostat or hot water tap to start heating.