Johnson Starley QuanTec 24C Fault codes & diagnostics

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

GC Number 47-416-13
Download the Johnson Starley QuanTec 24C manualThe official installation and service manual (PDF), the document these fault codes were read from. 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 →

Fault codes

All 5 documented codes

Tap any card for details

E-01

Your boiler has failed to start up after multiple attempts and has now locked itself out for safety reasons.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification sensor
Full explanation for E-01
E03

Your boiler has shut down because it has detected it is getting too hot, which is a safety feature to prevent damage.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open to allow water to flow.
  2. Ensure there are no blockages in the system by checking if any external pumps are running.
  3. Try resetting the boiler via the control panel once it has cooled down.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Temperature Sensor (NTC)

Related codes

Full explanation for E03
F-15

Your boiler has stopped working because it has been manually reset too many times in a short window, suggesting an underlying fault that needs professional attention.

High Engineer only £120-350

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)
Full explanation for F-15
F37

Your boiler has stopped working because the water pressure in the central heating system has dropped too low.

High DIY-safe £0-160

What to check first

  1. Locate the metal braided filling loop underneath or near your boiler.
  2. Slowly open the one or two valves on the loop until you hear water flowing.
  3. Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the valves tightly.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor
Full explanation for F37
F40

Your boiler has detected that the water pressure in the central heating system is too low or too high for it to operate safely.

High DIY-safe £0-160

What to check first

  1. Check the pressure gauge on the front of the boiler or under the casing; it should be between 1.0 and 1.5 bar.
  2. If it is below 1.0, use the external filling loop valves to top up the system until the needle reaches the green zone.
  3. If the pressure is too high, bleed a radiator to release water and lower the pressure.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor
Full explanation for F40
Boiler cover options

Avoid the next call-out bill

Monthly cover means no unexpected bills when your boiler breaks down.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.