Baxi Suprima 70 Fault codes & diagnostics

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

Regular Natural Gas 20.5 kW 1999-2010 Discontinued
GC Number 41-607-79

Replaced by: Potterton Promax HE

Download the Baxi Suprima 70 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 →

Severity at a glance

Each cell = one fault code. Hover to identify.
14 High 2 Medium 3 Low
Just want the most common Baxi Suprima 70 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 19 documented codes

Tap any card for details

LED / flash-pattern codes
1 red flash

Your boiler has detected that it is getting too hot or that water isn't moving through the system correctly, causing it to shut down for safety.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the system pressure is between 1 and 1.5 bar on the external gauge
  3. Try resetting the boiler by pressing the reset button for 5 seconds
  4. Check if the pump is running or if there is an obvious blockage in the pipes

Parts commonly replaced

  • Temperature thermistor (NTC sensor)
  • Circulating pump
  • Overheat thermostat

Related codes

Full explanation for 1 red flash
2 red flashes

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

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves (TRVs) are turned fully open
  2. Ensure the system water pressure is between 1 and 1.5 bar on the gauge
  3. Press the reset button once to see if the boiler restarts

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Thermistor

Related codes

Full explanation for 2 red flashes
3 red flashes

Your boiler has tried to light several times but cannot establish a flame, leaving you without heating and hot water.

High DIY-safe £120-350

What to check first

  1. Check if your gas supply is active by testing another gas appliance like a hob
  2. Ensure there is credit on your gas meter if you have a prepayment plan
  3. Press the 'Reset' button firmly for two seconds to allow the boiler to try again

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • PCB (Printed Circuit Board)

Related codes

Full explanation for 3 red flashes
4 green flashes

Your boiler is having a temporary 'conversation' issue between its internal parts and should fix itself momentarily without you needing to do anything.

Low DIY-safe £0-120

What to check first

  1. Wait for the boiler to automatically reset itself
  2. If the flashing continues for more than 10 minutes, turn the control knob to reset and back to the desired temperature
  3. Ensure the power supply to the boiler is stable and not being interrupted

Parts commonly replaced

  • None (self-correcting)
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 4 green flashes
4 red flashes

Your boiler's internal cooling and exhaust fan is not spinning or communicating correctly, preventing the system from starting up for safety.

High Engineer only £250-£450

Parts commonly replaced

  • Fan Assembly
  • Printed Circuit Board (PCB)
  • Air Pressure Switch

Related codes

Full explanation for 4 red flashes
5 green flashes

Your boiler has experienced a temporary electronic glitch in its control system, but it is programmed to fix itself and restart automatically.

Low DIY-safe £0-280

What to check first

  1. Wait for the boiler to complete its self-reset process
  2. If the flashing continues for more than 30 minutes, turn the power switch off and back on again
  3. Monitor the boiler to see if the fault recurs frequently

Parts commonly replaced

  • Printed Circuit Board (PCB)
Full explanation for 5 green flashes
5 red flashes

Your boiler's internal memory or brain is experiencing a technical failure, meaning it can no longer remember how to operate correctly.

High Engineer only £180-350

Parts commonly replaced

  • Parameter Storage Unit (PSU)
  • Main PCB (Control Board)

Related codes

Full explanation for 5 red flashes
6 green flashes

Your boiler has encountered a minor temporary glitch and is currently trying to restart itself automatically.

Low DIY-safe £0-80

What to check first

  1. Wait up to 15 minutes to see if the boiler resets itself automatically.
  2. If the flashing persists, press the reset button firmly for 2 to 3 seconds.
  3. Check that your gas and electricity supplies haven't been interrupted.

Parts commonly replaced

  • None (Software reset)
  • PCB (if fault recurs frequently)

Related codes

Full explanation for 6 green flashes
6 red flashes

Your boiler has encountered a general electrical or internal system error that is preventing it from running properly.

High DIY-safe £180-450

What to check first

  1. Locate the reset button on the front control panel.
  2. Press and hold the reset button for 5 to 10 seconds.
  3. Wait for the indicator light to turn green; if the red flashes return, a technician is required.

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • External wiring harness
  • Ignition electrodes

Related codes

Full explanation for 6 red flashes
Digital codes
110

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

High DIY-safe £120-280

What to check first

  1. Check if your radiator valves are open
  2. Bleed your radiators using a radiator key to remove trapped air
  3. Once the boiler has cooled, press the reset button

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Thermistor

Related codes

Full explanation for 110
125

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

High DIY-safe £180-350

What to check first

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

Parts commonly replaced

  • Central heating pump
  • Flow / Return thermistors
  • Main PCB

Related codes

Full explanation for 125
127

Your boiler has failed to heat your hot water tank to a high enough temperature to kill off potentially harmful bacteria.

Medium DIY-safe £90-220

What to check first

  1. Check that your hot water cylinder thermostat is not turned down too low.
  2. Ensure your hot water 'on' times are long enough for the tank to reach full temperature.
  3. Press the reset button on the boiler faceplate.

Parts commonly replaced

  • Cylinder Thermostat
  • NTC Thermistor
  • PCB (Printed Circuit Board)

Related codes

Full explanation for 127
133

Your boiler is trying to light, but the burner isn't staying on or starting up as it should.

High DIY-safe £100-350

What to check first

  1. Check if your gas prepay meter has credit
  2. Ensure other gas appliances in the home are working
  3. Press the Reset button once to see if the boiler restarts

Parts commonly replaced

  • Gas valve
  • Ignition lead
  • Electrode
  • PCB

Related codes

Full explanation for 133
160

Your boiler has stopped working because the internal fan, which safely exhausts gases, is not spinning or communicating correctly with the system.

High Engineer only £200-£350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Air pressure switch

Related codes

Full explanation for 160
E12

Your boiler has detected that water isn't moving through the system correctly, which has caused it to shut down to prevent overheating.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure your external heating pump is running if accessible
  3. Gently bleed your radiators to remove any trapped air
  4. Reset the boiler using the reset button

Parts commonly replaced

  • External Central Heating Pump
  • Differential Pressure Switch
  • Flow Pipe Thermistor

Related codes

Full explanation for E12
E78

Your boiler has detected an issue with the sensor that monitors internal water pressure, meaning it cannot confirm if there is enough water to run safely.

High Engineer only £140-£220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Main PCB

Related codes

Full explanation for E78
OFF OFF OFF

Your boiler has no electricity reaching it and the display has completely shut down.

High DIY-safe £60-£250

What to check first

  1. Check if your home's main fuse box (consumer unit) has tripped a switch.
  2. Ensure the boiler's power switch or fused spur on the wall is turned on.
  3. Replace the 3-amp fuse in the boiler's external power plug or wall switch.

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • External 3A Fuse
  • Wiring harness
Full explanation for OFF OFF OFF
ON OFF ON

Your boiler has tried to start up but failed to light the flame, causing the system to shut down for safety.

High DIY-safe £100-350

What to check first

  1. Check that your gas emergency control valve is open and you have credit on your gas meter.
  2. Press the reset button once for five seconds to see if the boiler restarts.
  3. Ensure there are no external obstructions to the flue terminal outside.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • PCB (Printed Circuit Board)
Full explanation for ON OFF ON
Status & diagnostic codes

1 operating states & engineer diagnostics

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

1 green flash Status Your boiler has reached its set temperature and is temporarily resting; it is working exactly as it should.