Keston Heat 55 Fault codes & diagnostics

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

Regular Natural Gas 55 kW 2013 onwards Discontinued
GC Number 41-930-41

Replaced by: Keston Heat 55 2

Download the Keston Heat 55 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
41-930-41 Heat 55 2013–present
Fault codes

All 2 documented codes

Tap any card for details

E18

Your boiler has detected that the water inside is getting too hot because it is not moving around your heating system quickly enough.

High DIY-safe £150-£450

What to check first

  1. Check that at least two or three radiator valves are fully open to allow water flow.
  2. Ensure your external heating pump (if visible) is running and not making a loud humming noise.
  3. Check your boiler pressure gauge and top it up to 1.5 bar if it is too low.

Parts commonly replaced

  • External Circulation Pump
  • Heat Exchanger (Powerflush required)
  • Flow/Return Thermistors
Full explanation for E18
L5

Your boiler has been manually reset too many times in a short period and has locked itself out as a safety precaution.

High DIY-safe £0-120

What to check first

  1. Switch the electricity supply to the boiler off at the fused spur switch
  2. Wait for 30 seconds
  3. Switch the power back on to clear the temporary lockout

Parts commonly replaced

  • No parts usually required
  • Ignition Electrode (if underlying ignition fault exists)
  • PCB (if software fault)

Related codes

Full explanation for L5