Vokera Hydra Fault codes & diagnostics

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

Combi Natural Gas 24 kW 1994-1999 Discontinued

Replaced by: Linea

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Severity at a glance

Each cell = one fault code. Hover to identify.
2 Emergency 41 High 3 Low
Just want the most common Vokera Hydra faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 46 documented codes

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b 18

Your boiler has detected that the water inside the unit is dangerously hot and has shut itself down to prevent damage or overheating.

Emergency DIY-safe £150-300

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar
  3. Reset the boiler following the manufacturer instructions once it has cooled down

Parts commonly replaced

  • NTC Temperature Sensor
  • Primary Heat Exchanger
  • Pump

Related codes

Full explanation for b 18
b 19

Your boiler has detected that the water returning from your radiators is dangerously hot, causing it to shut down to prevent damage.

High DIY-safe £150-250

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure there are no obstructions to the air vents
  3. Reset the boiler using the control knob once the system has cooled down

Parts commonly replaced

  • Return NTC sensor
  • Pump
  • Primary heat exchanger

Related codes

Full explanation for b 19
b 24

Your boiler is confused because the water leaving it is cooler than the water returning, suggesting a flow problem or a faulty sensor reading.

High Engineer only £150-300

Parts commonly replaced

  • NTC temperature sensor
  • Central heating pump
  • Flow switch

Related codes

Full explanation for b 24
b 25

Your boiler is overheating because it cannot circulate heat away from the burner fast enough, so it has safely shut itself down to prevent damage.

High DIY-safe £150-300

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the central heating system pressure is between 1.0 and 1.5 bar
  3. Press the reset button once the boiler has cooled down

Parts commonly replaced

  • Pump
  • Diverter valve
  • Heat exchanger
  • NTC sensor

Related codes

Full explanation for b 25
b 26

Your boiler is unable to drain the water it produces during normal operation, which is causing it to shut down to prevent internal damage.

High DIY-safe £90-160

What to check first

  1. Check the white plastic pipe leading outside to see if it is frozen or blocked.
  2. If frozen, gently pour warm (not boiling) water over the external pipe to melt the ice.
  3. Carefully check the plastic trap underneath the boiler for visible blockages if accessible without opening the boiler casing.
  4. Restart the boiler once the blockage is cleared.

Parts commonly replaced

  • Condensate trap
  • Condensate hose
  • Sump assembly

Related codes

Full explanation for b 26
b 28

Your boiler has stopped working because it cannot communicate with the internal motor that clears out exhaust gases.

High Engineer only £150-250

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for b 28
b 29

Your boiler is struggling to communicate with its internal air-flow system, which prevents it from safely igniting and providing heating or hot water.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for b 29
b 30

Your boiler has detected that the water is not circulating properly, meaning it is getting too hot inside the unit compared to the temperature of the water being sent out to your radiators.

High DIY-safe £120-250

What to check first

  1. Check that your radiator valves are open to allow water flow
  2. Check the boiler pressure gauge and top up to 1.5 bar if it is low
  3. Bleed your radiators to remove any trapped air pockets
  4. Reset the boiler using the control dial

Parts commonly replaced

  • Central Heating Pump
  • Plate Heat Exchanger
  • Diverter Valve

Related codes

Full explanation for b 30
b 65

Your boiler is failing to start because it cannot detect that the fan is moving fast enough to clear out exhaust gases safely.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • Venturi
  • Air pressure switch
  • PCB
Full explanation for b 65
b/E 18

Your boiler is unable to move water around the system because the pump is stuck or a valve has been accidentally closed.

High DIY-safe £180-350

What to check first

  1. Check that the isolation valves underneath the boiler are in the open position (parallel to the pipework).
  2. Ensure all radiator valves are open to allow water to circulate.
  3. Try resetting the boiler to see if the pump clears its own blockage.

Parts commonly replaced

  • Circulation Pump
  • Pump Capacitor
Full explanation for b/E 18
Showing 11–20 of 46
c OF

Your boiler is currently set to a standby mode where the central heating function has been manually turned off at the controls.

Low DIY-safe

What to check first

  1. Locate the mode selector or display panel on the front of the boiler
  2. Press the heating button or adjust the winter/summer mode setting to enable the central heating
  3. Increase the temperature setting on your connected room thermostat to trigger a demand for heat
Full explanation for c OF
E 00

Your boiler is detecting a flame inside the combustion chamber when it should be switched off, which is a safety concern that prevents it from firing.

Emergency Engineer only £150-300

Parts commonly replaced

  • Flame rectification electrode
  • Gas valve
  • Printed circuit board (PCB)

Related codes

Full explanation for E 00
E 02

Your boiler is failing to light the fuel inside, so it has safely shut down to prevent gas from building up.

High DIY-safe £120-250

What to check first

  1. Check if other gas appliances, like a gas hob, are working to ensure gas is reaching the property
  2. Check that your gas meter has credit if you use a pre-payment meter
  3. Press the Reset button or turn the dial to 'Reset' for a few seconds to see if the boiler restarts

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for E 02
E 03

Your boiler's main internal computer is failing to communicate correctly, which has caused the system to stop working entirely for safety reasons.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for E 03
E 04

Your boiler has stopped working because it has detected a major internal error that has forced it to shut down for safety reasons.

High DIY-safe £150-350

What to check first

  1. Check if your main electrical consumer unit (fuse box) has any tripped switches.
  2. Ensure the boiler's power isolation switch is turned on.
  3. If power is present, try to reset the boiler using the control knob or reset button.

Parts commonly replaced

  • Printed circuit board
  • Wiring harness
  • Ignition transformer

Related codes

Full explanation for E 04
E 05

Your boiler's internal computer is experiencing a communication error and cannot safely operate the system.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for E 05
E 06

Your boiler's internal computer has flagged a critical error that prevents it from starting up or operating safely.

High Engineer only £250-450

Parts commonly replaced

  • Main Control PCB

Related codes

Full explanation for E 06
E 07

Your boiler has detected a failure within its main control board and has safety-locked itself to prevent incorrect operation.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
Full explanation for E 07
E 11

Your boiler's internal electronic brain has encountered a serious error and is unable to operate safely, causing the system to shut down.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for E 11
Showing 21–30 of 46
E 12

Your boiler has detected that the water temperature in your underfloor heating circuit is outside of the expected safe range, causing the system to stop working.

High Engineer only £120-250

Parts commonly replaced

  • Underfloor temperature sensor
  • Mixing valve actuator
  • Circulation pump

Related codes

Full explanation for E 12
E 13

Your boiler's main control unit has identified a critical internal software or hardware error and must shut down to prevent further damage.

High Engineer only £250-450

Parts commonly replaced

  • Main printed circuit board (PCB)

Related codes

Full explanation for E 13
E 14

Your boiler's main control unit has detected an internal electronic error and has stopped working to prevent further damage.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for E 14
E 15

Your boiler's internal computer has encountered a serious error and can no longer control the system, meaning your heating and hot water will not work.

High Engineer only £250-450

Parts commonly replaced

  • Main printed circuit board (PCB)

Related codes

Full explanation for E 15
E 16

Your boiler's electronic control system has detected an internal failure, which is preventing it from operating correctly.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB

Related codes

Full explanation for E 16
E 17

Your boiler has detected an internal electronic error within its control brain, which means it has safely shut down to prevent incorrect operation.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)

Related codes

Full explanation for E 17
E 18

Your boiler has detected that the water temperature has risen too high and has safely shut itself down to prevent damage.

High DIY-safe £150-250

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  3. Switch the boiler off and on again to see if the fault clears after cooling

Parts commonly replaced

  • NTC temperature sensor
  • Central heating pump
  • PCB

Related codes

Full explanation for E 18
E 19

Your boiler has detected that the water returning to it from your radiators is too hot, causing the system to shut down to prevent damage.

High DIY-safe £120-250

What to check first

  1. Check that at least two or three radiators have their valves fully open
  2. Ensure your magnetic system filter is clean and not blocked
  3. Check if the pump is running or if there is a blockage in the pipework

Parts commonly replaced

  • Return NTC sensor
  • Primary heat exchanger
  • Pump

Related codes

Full explanation for E 19
E 25

Your boiler has sensed that the water inside is heating up far too quickly and has shut itself down to prevent damage.

High DIY-safe £120-250

What to check first

  1. Check if your radiator valves are open
  2. Ensure the system water pressure is between 1 and 1.5 bar
  3. Gently bleed your radiators to remove trapped air

Parts commonly replaced

  • Pump
  • System filter
  • Heat exchanger

Related codes

Full explanation for E 25
E 28

Your boiler has stopped working because it cannot detect that the internal fan, which is essential for safely venting exhaust gases, is running.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E 28
Showing 31–40 of 46
E 29

Your boiler has detected that the internal fan responsible for safely venting fumes is not communicating correctly with the main control board.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E 29
E 30

Your boiler has detected that the water is heating up or circulating much faster than it should be, causing the system to shut down for safety.

High DIY-safe £120-250

What to check first

  1. Check that your system pressure is between 1.0 and 1.5 bar on the pressure gauge.
  2. Ensure all radiator valves are fully open to allow water to circulate.
  3. Restart the boiler using the reset button/dial to see if the fault clears.

Parts commonly replaced

  • Pump
  • Diverter valve
  • Primary heat exchanger
  • Temperature sensors

Related codes

Full explanation for E 30
E 31

Your boiler has detected an electrical fault in the part that measures the temperature of the water being sent to your radiators, which prevents it from heating properly.

High Engineer only £120-220

Parts commonly replaced

  • Flow NTC sensor
  • Wiring harness

Related codes

Full explanation for E 31
E 32

Your boiler has detected a faulty electrical signal from the pipe that brings water back into it, which is preventing the system from heating up correctly.

High Engineer only £120-200

Parts commonly replaced

  • Return NTC sensor
  • Wiring harness

Related codes

Full explanation for E 32
E 33

Your boiler has detected an electrical fault with one of its temperature sensors, meaning it cannot accurately read the heat levels and will stop working to keep you safe.

High Engineer only £120-220

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness

Related codes

Full explanation for E 33
E 36

Your boiler has lost the ability to detect the flow of water, so it has shut down to prevent damage from overheating.

High Engineer only £150-250

Parts commonly replaced

  • Flow sensor
  • Wiring harness

Related codes

Full explanation for E 36
E 37

Your boiler has lost the ability to read the temperature of the water returning to it, so it has safely shut down to prevent overheating.

High Engineer only £120-180

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness

Related codes

Full explanation for E 37
E 38

Your boiler is struggling to detect the temperature of the water coming into the unit, so it has shut down to prevent any damage.

High Engineer only £120-200

Parts commonly replaced

  • Inlet temperature sensor
  • Wiring harness

Related codes

Full explanation for E 38
E 44

Your boiler has detected an internal electronic error within its main control brain, meaning it has safely shut itself down to prevent further issues.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
Full explanation for E 44
E 60

Your boiler's internal computer is struggling to read its own settings, meaning it has temporarily stopped working to prevent incorrect operation.

High Engineer only £150-300

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Wiring harness
Full explanation for E 60
Showing 41–46 of 46
E 65

Your boiler's fan is not spinning fast enough to clear waste gases safely, so it has shut down to prevent a hazard.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Flue sensor
Full explanation for E 65
Test 1A

Your boiler has lost power to its control screen, making it impossible to operate the heating or hot water, even though some internal parts are still trying to move.

High Engineer only £150-300

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Power supply unit

Related codes

Full explanation for Test 1A
Test 2

Your boiler is unable to move the water around the system, which means it cannot heat your home or provide hot water.

High Engineer only £180-350

Parts commonly replaced

  • Central heating pump
  • Pump capacitor
  • PCB
Full explanation for Test 2
Test 3

Your boiler has detected that the internal mechanism responsible for clearing exhaust gases is not operating correctly, so it has safely shut down to prevent any unsafe build-up.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • Fan wiring harness
  • PCB
Full explanation for Test 3
Test 4

Your boiler is failing to light the burner, meaning it cannot produce heating or hot water safely.

High DIY-safe £120-250

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas is reaching your home.
  2. Verify that your gas meter has credit if you use a pre-payment system.
  3. Try resetting the boiler by turning the control knob to the 'Reset' position and holding it for a few seconds.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition transformer

Related codes

Full explanation for Test 4