Potterton Precision Fault codes & diagnostics

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

Regular Natural Gas 2001-2015 Discontinued
GC Number 41-592-33
Download the Potterton Precision manualThe official installation and service manual (PDF), the document these fault codes were read from. 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 →

Severity at a glance

Each cell = one fault code. Hover to identify.
12 High
Just want the most common Potterton Precision faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 12 documented codes

Tap any card for details

LED / flash-pattern codes
Flash Flash On

Your boiler has shut itself down for safety because a part that moves air through it isn't working correctly, so it won't provide heating or hot water until a qualified engineer has looked at it.

High Engineer only £150-350

What to check first

  1. Check that the flue outlet outside your home is not blocked by leaves, nesting material, snow, or debris, and clear any obstruction you can reach safely.
  2. Check that the boiler has mains power and that any external controls or thermostat are switched on.
  3. Press the reset button once, wait 5 minutes, and see if the boiler restarts. If the code returns, stop and call a Gas Safe registered engineer.

Parts commonly replaced

  • Fan assembly
  • Fan pressure switch
  • Flue hose or flue seals
  • Condensate trap

Related codes

Full explanation for Flash Flash On
Flash Off Flash

Your boiler has shut down because the electricity reaching your home is too weak for it to work safely, which usually points to a problem with the power supply rather than the boiler itself.

High Engineer only £0-200

What to check first

  1. Check whether other appliances in your home, or those of your neighbours, are also running poorly or have gone off, which would suggest a local supply problem.
  2. Check that the boiler's own electrical fuse or isolator switch is intact and that no other switches or controls have tripped, then try resetting the boiler once as the manual advises.
  3. If the boiler still shows Flash Off Flash, contact your electricity network operator (call 105 free of charge from any UK phone) to report low voltage, and book a heating engineer or electrician to check the wiring to the boiler if the supply is confirmed normal.

Parts commonly replaced

  • Boiler fuse
  • External wiring connections
  • Power supply cable
Full explanation for Flash Off Flash
Flash Off On

Your boiler has switched itself off to protect itself because it got too hot, and it will need a reset once it has cooled down and the cause has been checked.

High Engineer only £90-200

What to check first

  1. Turn the boiler off at the switch and leave it for at least 30 minutes to cool down.
  2. Check the pressure gauge on the front of the boiler and top it up to between 1 and 1.5 bar if it is low, following the filling loop instructions in the manual.
  3. Make sure all radiator valves are open and the boiler is not blocked by furniture or other objects, then turn it back on once. If it locks out again, call a Gas Safe registered engineer.

Parts commonly replaced

  • Overheat thermistor (NTC sensor)
  • Circulation pump
  • Heat exchanger (if scaled or blocked)

Related codes

Full explanation for Flash Off On
Flash On Flash

Your boiler's main control board appears to have failed, so it is stopped and will need a qualified engineer to replace the part before it can heat your home or water again.

High Engineer only £180-350

What to check first

  1. Check that the boiler has power and that the gas supply is turned on at the meter and the boiler's isolation valve.
  2. Switch the boiler off at its spur or fused switch, wait 30 seconds, then switch it back on to see if the fault clears.
  3. If the flashing returns, stop and call a Gas Safe registered engineer.

Parts commonly replaced

  • Printed circuit board (PCB)
  • Control board fuse
Full explanation for Flash On Flash
Flash On On

Your boiler's main control unit has a fault, so it may not be able to start up or run heating and hot water properly until a qualified engineer repairs or replaces it.

High Engineer only £200-350

What to check first

  1. Check that the boiler has mains power and that no isolator switch or fused spur has been turned off
  2. Switch the boiler off at the isolator, wait 60 seconds, then switch it back on once
  3. If the code returns, stop and contact a Gas Safe registered engineer to replace the control board

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Control board fuse

Related codes

Full explanation for Flash On On
On Flash Flash

Your boiler has shut itself down as a safety precaution, most often because it is low on water, so it needs a quick check before it can heat your home again.

High DIY-safe £90-220

What to check first

  1. Check the boiler's pressure gauge with the boiler cold. A reading below 1 bar usually means the system is low on water.
  2. If the pressure is low, top it up using the filling loop, following the boiler manual, and watch the gauge until it reaches about 1.5 bar.
  3. Close the filling loop, then press the reset button and see whether the boiler restarts.
  4. If the code returns, or the pressure keeps dropping, stop and call a Gas Safe registered engineer, as this may point to a leak or a faulty pump or flow switch.

Parts commonly replaced

  • Circulating pump
  • Flow switch
  • Diverter valve
  • Pressure relief valve

Related codes

Full explanation for On Flash Flash
On Flash On

Your boiler is showing a temperature sensor fault, which usually means it can't read the water temperature correctly and may stop heating or switch itself off as a safety precaution.

High Engineer only £90-180

What to check first

  1. Turn the boiler off at the control panel and at the isolator switch, wait 10 minutes, then turn it back on to reset it.
  2. Check the boiler pressure gauge and top up with the filling loop only if it reads below 1 bar, following the manufacturer's instructions.
  3. If the fault returns, stop and contact a Gas Safe registered engineer rather than opening the boiler casing.

Parts commonly replaced

  • Thermistor (flow or return temperature sensor)
  • Sensor wiring or connector
  • Control PCB (if the sensor is fine but the board is faulty)

Related codes

Full explanation for On Flash On
On Off Flash

The boiler has detected that the electricity supply wires to it are connected the wrong way round, so it has stopped working until a qualified electrician checks and corrects the wiring.

High Engineer only £80-180

Parts commonly replaced

  • Socket outlet
  • Fused spur or connection unit
  • Mains supply cable

Related codes

Full explanation for On Off Flash
On On Flash

Your boiler's main control board has developed a fault, so it has stopped working properly and will need a qualified engineer to replace it.

High Engineer only £200-350

What to check first

  1. Check that the boiler has power and that the external fuse or isolator switch is on.
  2. Turn the boiler off at the isolator, wait 5 minutes, then turn it back on.
  3. If the light still shows the same flashing pattern, leave the boiler off and book a Gas Safe registered engineer.

Parts commonly replaced

  • Printed circuit board (PCB)
  • Control board fuse

Related codes

Full explanation for On On Flash
Digital codes
Off Off Off

The boiler appears to have no power at all, so it isn't producing heating or hot water, but this is usually caused by a switch, fuse or power supply issue that can often be checked safely.

High DIY-safe £80-300

What to check first

  1. Check that the boiler's on/off switch is turned on and that the power switch on the wall (fused spur) is switched on with its fuse intact.
  2. Check your consumer unit (fuse box) to see whether the circuit for the boiler has tripped, and reset it if so.
  3. Check that the room thermostat or timer is not switching the boiler off, and replace its batteries if it has any.
  4. If the boiler still shows no display after these checks, stop and call a Gas Safe registered engineer, as the fault is likely inside the boiler's electrical circuit.

Parts commonly replaced

  • Fused spur or boiler power fuse
  • Main printed circuit board (PCB)
  • Power supply transformer
  • On/off switch
Full explanation for Off Off Off
On Off On

The boiler has stopped trying to light after several failed attempts, so it has shut itself down as a safety precaution and will need to be reset and checked.

High Engineer only £90-280

What to check first

  1. Check that the gas supply is turned on at the meter and that other gas appliances work.
  2. Check the boiler pressure gauge reads between 1 and 1.5 bar, and top up using the filling loop only if the pressure is low.
  3. Press and hold the reset button for about 3 seconds, or switch the boiler off and on, then wait 5 minutes before trying again.
  4. If the boiler locks out again, stop and call a Gas Safe registered engineer. If you smell gas, leave the property, open windows, and call the National Gas Emergency number on 0800 111 999.

Parts commonly replaced

  • Ignition electrode
  • Flame sensor
  • Ignition lead
  • Gas valve
  • Printed circuit board (PCB)

Related codes

Full explanation for On Off On
On On On

Your boiler is showing a display pattern that suggests an internal wiring or control connection may have come loose or failed, and it needs a qualified engineer to check it safely.

High Engineer only £100-220

Parts commonly replaced

  • Output selector switch
  • LV wiring harness
  • 8-way PCB connector
Full explanation for On On On