Baxi Solo 3 PFL Fault codes & diagnostics

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

Regular Natural Gas 8.8-23.4 kW 1994-2005 Discontinued

Replaced by: Baxi Solo 3 HE

This boiler uses indicator light combinations

Note which lights are on, off, or flashing and at what speed. Match the combination to the cards below. Do not reset until you have noted the pattern. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
2 Emergency 7 High 4 Low
Just want the most common Baxi Solo 3 PFL faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 13 documented codes

Tap any card for details

LED / flash-pattern codes
Overheat indicator light

Your boiler has switched itself off because it got too hot or experienced a power cut, and it simply needs to be manually reset to start working again.

High DIY-safe £0-150

What to check first

  1. Locate the overheat reset button on the bottom of the boiler control box
  2. Press the reset button firmly
  3. Wait for the boiler to restart and check if the light has gone out

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Flow/Return Sensor
Full explanation for Overheat indicator light
Digital codes
Lockout

Your boiler has stopped working because it has detected a temperature that is too high and has temporarily disabled itself for safety.

High DIY-safe £0-120

What to check first

  1. Turn the boiler control knob to the 'OFF' position.
  2. Wait for at least 10 seconds to allow the system to reset.
  3. Turn the control knob back to your desired setting.

Parts commonly replaced

  • Overheat Thermostat
  • Pump
  • Temperature Sensor

Related codes

Full explanation for Lockout
lockout light

Your boiler has detected a safety issue and stopped working to protect your home, meaning you currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition lead
  • Gas valve
  • PCB
  • Flame rectification probe
Full explanation for lockout light
Overheat

Your boiler has become too hot and has automatically shut itself down to prevent damage or safety issues.

High DIY-safe £100-280

What to check first

  1. Check that your radiator valves are open to allow water to circulate
  2. Let the boiler cool down for 15 to 30 minutes
  3. Press the reset button or turn the control knob to the 'Off' position and then back to 'On'

Parts commonly replaced

  • Circulation pump
  • Overheat thermostat
  • Flow temperature sensor

Related codes

Full explanation for Overheat
Overheat light

Your boiler has become too hot and has automatically shut down as a safety precaution to prevent damage.

High DIY-safe £100-300

What to check first

  1. Locate the thermostat control knob on the boiler front panel.
  2. Turn the knob fully anticlockwise to the 'OFF' position.
  3. Wait 10 seconds, then turn the knob back to your desired temperature setting to reset the light.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Heat Exchanger (de-scaling)

Related codes

Full explanation for Overheat light
Overheat Neon

Your boiler has detected that it is getting too hot and has automatically shut itself down to prevent damage.

Emergency Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Pump
  • PCB
  • Diverter valve

Related codes

Full explanation for Overheat Neon
Overheat Neon Illumination

Your boiler has switched itself off because it has reached a temperature that is too high, and it needs to be manually reset once it has cooled down.

High DIY-safe £90-250

What to check first

  1. Wait for the boiler to cool down completely
  2. Locate the reset button on the control box under the boiler
  3. Press the reset button and check if the neon light goes out and the boiler restarts

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger
Full explanation for Overheat Neon Illumination
Pressure 3 or greater

Your boiler's internal water pressure has reached a dangerous level, causing a safety valve to activate to prevent damage.

Emergency Engineer only £120-250

Parts commonly replaced

  • Pressure relief valve
  • Pressure gauge
  • Expansion vessel
  • Filling loop
Full explanation for Pressure 3 or greater
Pressure below 1

Your boiler has lost the water pressure required to circulate heat around your home, likely due to a small leak somewhere in your radiator system.

High DIY-safe £80-150

What to check first

  1. Locate the external filling loop, which is a silver braided hose connecting your central heating pipes.
  2. Open the valves at both ends of the filling loop to allow cold mains water into the system.
  3. Watch the pressure gauge on the boiler front until the needle reaches the green zone (typically 1.0 to 1.5 bar).
  4. Close both valves firmly and check that the pressure remains steady.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Expansion vessel
Full explanation for Pressure below 1