Viessmann Vitodens 100-W BPJA 21kW P25 Fault codes & diagnostics

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

Combi Natural GasLPG 2012-2015 Discontinued
GC Number 47-819-26
Download the Viessmann Vitodens 100-W BPJA 21kW P25 manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
2 Emergency 19 High
Just want the most common Viessmann Vitodens 100-W BPJA 21kW P25 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 21 documented codes

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5A

Your boiler has shut itself down because one of its water temperature sensors has lost its connection or failed, so it can't safely heat your home or water until it's checked.

High Engineer only £120-250

What to check first

  1. Check the boiler pressure gauge: it should read between 1 and 1.5 bar when cold. If it is low, top it up using the filling loop, following the boiler manual.
  2. Press and hold the reset button on the boiler for about 3 seconds, or use the reset option on the controls, and wait a few minutes to see if the boiler restarts.
  3. If the fault returns straight away, stop trying to reset it and book a Gas Safe registered engineer.

Parts commonly replaced

  • Flow temperature sensor (NTC)
  • Sensor wiring lead or harness
  • Main PCB (control board), in some cases

Related codes

Full explanation for 5A
30

Your boiler has stopped because it has lost track of the water temperature reading it uses to run safely, so it has switched itself off until a qualified engineer checks it.

High Engineer only £120-220

What to check first

  1. Check the pressure gauge on the front of the boiler. It should read between 1.0 and 2.0 bar when cold. If it is low, the boiler may stop for safety, so top it up using the filling loop only if you know how to do this safely.
  2. Press the reset button (the small button or the reset symbol on the control panel) once and wait about 10 minutes to see if the boiler restarts.
  3. If the fault code returns, stop trying to fix it and call a Gas Safe registered engineer.

Parts commonly replaced

  • Boiler water temperature sensor (NTC sensor)
  • Sensor wiring harness or plug
  • Control PCB (only if the sensor and wiring are fine)

Related codes

Full explanation for 30
38

Your boiler has stopped working because it cannot read its water temperature sensor properly, so it has shut itself down as a safety precaution and will need a qualified engineer to check it.

High Engineer only £120-250

What to check first

  1. Check the boiler pressure gauge and make sure it reads between 1 and 1.5 bar when cold. If it is low, top it up using the filling loop only if you know how to do so safely.
  2. Turn the boiler off at the switch, wait 30 seconds, then turn it back on to see whether the fault clears.
  3. If the fault returns, do not keep resetting the boiler. Leave it off and book a Gas Safe registered engineer.

Parts commonly replaced

  • Boiler water temperature sensor (NTC)
  • Sensor lead or wiring harness
  • Burner assembly (if blocked or damaged)

Related codes

Full explanation for 38
51

The boiler has detected a faulty temperature sensor that controls the hot water, so it has stopped heating water for taps and showers, though your central heating may still work.

High Engineer only £120-220

What to check first

  1. Switch the boiler off at its on/off switch and at the fused spur or isolator, wait 5 minutes, then switch it back on to see whether the fault clears.
  2. Check that the boiler has gas and water pressure (the pressure gauge should read between 1 and 1.5 bar when cold), and top up with the filling loop only if the pressure is low.
  3. If the code returns, leave the boiler off and book a Gas Safe registered engineer, as the sensor needs checking and replacing and should not be opened by a homeowner.

Parts commonly replaced

  • DHW outlet temperature sensor (Viessmann Vitodens type)
  • Sensor cable or plug connector
  • Main PCB (only if the sensor and wiring test good but the fault remains)

Related codes

Full explanation for 51
52

Your boiler has shut itself down as a precaution because it has detected a fault with the sensor that measures the water temperature leaving the boiler, so it isn't able to heat your home or water safely until this is checked.

High Engineer only £150-250

What to check first

  1. Check the pressure gauge on the front of the boiler. It should read between 1 and 1.5 bar when cold. If it is low, top it up using the filling loop, following the boiler manual.
  2. Turn off the boiler at its power supply and wait 10 minutes.
  3. Turn the boiler back on and press the reset button. If the code returns, stop and call a Gas Safe registered engineer.

Parts commonly replaced

  • Flow temperature sensor
  • Sensor wiring harness
  • Main PCB (if the sensor circuit is damaged)

Related codes

Full explanation for 52
59

Your boiler has stopped heating the hot water from the tap, but your central heating may still work, and a sensor that checks the hot water temperature appears to have a connection problem that a heating engineer can usually fix.

High Engineer only £150-250

What to check first

  1. Switch the boiler off at its on/off switch and at the fused spur, then wait five minutes.
  2. Switch the boiler back on and check whether the fault code clears or returns after a few minutes.
  3. If the fault returns, stop and book a Gas Safe registered engineer to check the sensor and its wiring.

Parts commonly replaced

  • DHW outlet temperature sensor
  • Sensor plug and wiring harness
  • Sensor connection cable

Related codes

Full explanation for 59
b0

Your boiler has shut itself down because a sensor measuring the heat of its exhaust gases is sending a faulty signal, so it is stopping as a safety precaution.

High Engineer only £150-300

What to check first

  1. Check that the boiler has not been knocked or affected by a power cut, and that the pressure gauge reads between 1 and 1.5 bar when cold.
  2. Press the reset button once on the boiler, wait 5 minutes, and see whether it restarts.
  3. If it locks out again, stop and call a Gas Safe registered engineer. Do not open the boiler casing or try to bypass the sensor.

Parts commonly replaced

  • Flue gas temperature sensor
  • Sensor wiring harness
  • Control unit PCB (if the sensor is not the cause)

Related codes

Full explanation for b0
b8

Your boiler has shut itself down as a safety precaution because a sensor that checks the exhaust gases is not sending a reliable reading, so it may not be heating your home or water until it is looked at.

High Engineer only £150-300

What to check first

  1. Turn the boiler off at its on/off switch and wait about 10 minutes, then switch it back on to see if it restarts.
  2. From outside, check that the flue terminal (the pipe or grille where the boiler exhaust exits the wall) is not blocked by leaves, nesting material, snow, or debris, and clear any obstruction you can reach safely.
  3. If the boiler still shows b8 after one reset, stop trying to reset it and contact a Gas Safe registered engineer.

Parts commonly replaced

  • Flue gas temperature sensor
  • Sensor lead or wiring harness
  • Flue terminal (only if blocked or damaged)
  • Control PCB (only if the fault persists after sensor replacement)

Related codes

Full explanation for b8
E3

Your boiler has shut itself down as a safety precaution because it has detected a problem with its burner or one of its safety checks, so it can't heat your home or water until a qualified engineer has looked at it.

High Engineer only £120-350

What to check first

  1. Check that your gas supply is on by confirming your hob or other gas appliances work, and that your gas meter emergency control has not been turned off.
  2. Check the boiler pressure gauge on the front panel; if it reads below 1 bar, top it up using the filling loop as shown in your manual, then stop.
  3. Press the reset button once, wait 10 minutes, and see if the boiler restarts; if the E3 code returns, stop and call a Gas Safe registered engineer.

Parts commonly replaced

  • Ionisation (flame detection) electrode
  • Gas valve
  • Gas pressure switch
  • Fan assembly
  • Ignition electrode

Related codes

Full explanation for E3
E5

Your boiler has shut itself down because its burner appears to be blocked or has an internal problem, so it can't produce heat or hot water until a qualified engineer checks it.

High Engineer only £150-400

What to check first

  1. Check that the boiler has water pressure on its gauge, usually between 1 and 1.5 bar when cold, and top it up if it is low.
  2. Switch the boiler off at the unit and at the mains, wait 10 minutes, then switch it back on once to try a single reset.
  3. If the code returns, leave the boiler off and contact a Gas Safe registered engineer. Do not repeatedly reset it or open the casing.

Parts commonly replaced

  • Burner gasket
  • Burner assembly
  • Ignition electrode

Related codes

Full explanation for E5
Showing 11–20 of 21
F0

Your boiler has shut itself down for safety because its gas burner appears to be blocked or not working correctly, so it may not be providing heating or hot water until it is checked.

High Engineer only £150-400

What to check first

  1. Check the pressure gauge on the front of the boiler. It should read between 1 and 1.5 bar when cold. If it is low, top it up using the filling loop, or leave it for a Gas Safe engineer if you are unsure how.
  2. Press and hold the reset button or select reset on the display for a few seconds, then wait 10 to 15 minutes to see if the boiler restarts.
  3. Check that the outside flue terminal is clear of leaves, nests, snow or other debris, and that nothing is blocking the air vents. If the fault returns after a reset, stop and call a Gas Safe registered engineer rather than repeating the reset.

Parts commonly replaced

  • Burner assembly
  • Burner gasket
  • Fan assembly
  • Ignition electrode
  • Gas valve
  • Flue or air intake components

Related codes

Full explanation for F0
F1

The boiler has shut itself down because the hot gases leaving it through the flue got hotter than its safety limit, which usually means the flue is partly blocked or the boiler is not drawing air properly.

High Engineer only £150-350

What to check first

  1. Turn the boiler off at its on/off switch and wait about 10 minutes for it to cool.
  2. Check from outside, without climbing ladders, that the flue terminal (the pipe opening on the wall or roof) is not blocked by leaves, nesting material, or debris.
  3. Turn the boiler back on and press the reset button once. If the fault returns, or the boiler will not reset, stop and call a Gas Safe registered engineer.

Parts commonly replaced

  • Flue gas temperature limiter
  • Flue gas temperature sensor
  • Flue terminal or flue adaptor
  • Heat exchanger (if scaled or damaged)

Related codes

Full explanation for F1
F2

Your boiler has switched itself off because the water inside it got too hot, which is a built-in safety cut-out, and it will need a check before it can safely restart.

High Engineer only £150-350

What to check first

  1. Check the pressure gauge on the boiler. It should read between 1 and 1.5 bar when cold. If it is low, top it up using the filling loop as shown in the manual, then close the loop.
  2. Make sure all radiator valves and the boiler's flow and return valves are fully open, so water can circulate freely.
  3. Turn the boiler off at the switch, wait about 10 minutes for it to cool, then turn it back on and press the reset button once. If the F2 code returns, stop and call a Gas Safe registered engineer.

Parts commonly replaced

  • Safety temperature limiter (STB)
  • Flow temperature sensor
  • Circulation pump
  • Heating sensor (NTC)

Related codes

Full explanation for F2
F3

Your boiler's flame sensor is picking up a flame when the burner should be switched off, which can point to a gas valve or sensor problem, so please turn the boiler off and get a Gas Safe engineer to check it before using it again.

Emergency Engineer only £150-350

What to check first

  1. Turn the boiler off at its on/off switch and do not try to restart it.
  2. If you smell gas, open windows, avoid switches and flames, leave the property, and call the National Gas Emergency Service on 0800 111 999 from outside.
  3. Do not keep resetting the boiler, as repeated resets do not address the cause.
  4. Book a Gas Safe registered engineer to diagnose and repair the fault.

Parts commonly replaced

  • Gas valve
  • Ionisation (flame sensing) electrode
  • Printed circuit board (PCB)
  • Burner gasket

Related codes

Full explanation for F3
F4

The boiler started up but could not detect a flame, so it has shut itself down as a safety precaution and will need a qualified engineer to check the gas supply and burner.

High Engineer only £90-300

What to check first

  1. Check that the gas supply is on, including the isolation valve under or beside the boiler and any gas meter tap, and that other gas appliances are working.
  2. Check the boiler pressure gauge and top up with the filling loop if it is below about 1 bar, following the manufacturer's instructions.
  3. Press the reset button on the boiler once and wait a few minutes to see if it lights. If it fails again, stop and call a Gas Safe registered engineer.
  4. If you smell gas at any point, turn off the gas supply, open windows, do not use switches or flames, and call the National Gas Emergency Service on 0800 111 999.

Parts commonly replaced

  • Flame detection (ionisation) electrode
  • Ignition electrode
  • Gas valve
  • Control PCB

Related codes

Full explanation for F4
F8

The boiler has shut itself down as a safety precaution because one of its gas controls did not switch off quickly enough, so it needs a qualified Gas Safe engineer to check it before it is used again.

Emergency Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • Gas valve control module
  • Ignition electrode
  • Flame sensor

Related codes

Full explanation for F8
F9

Your boiler's internal fan, which helps it burn gas safely, isn't starting up, so the boiler is shutting itself down to protect itself and will likely stop providing heating and hot water until it's checked by a qualified engineer.

High Engineer only £200-400

What to check first

  1. Check that the boiler has mains power, the display is on, and the external power switch or fused spur is on.
  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 boiler manual.
  3. Press the reset button once and wait a few minutes to see if the boiler restarts normally.
  4. Check the flue terminal outside your home for obstructions such as leaves, nests or debris, and clear any you can safely reach.
  5. If the F9 code returns, stop trying to fix it and contact a Gas Safe registered engineer.

Parts commonly replaced

  • Combustion fan assembly
  • Fan power and signal cable
  • Main control PCB

Related codes

Full explanation for F9
FA

Your boiler has shut itself down because its burner and fan did not stop and reset properly, which is a safety protection, so heating and hot water may be off until it is checked.

High Engineer only £120-420

What to check first

  1. Check that the boiler has power and that the gas supply tap to the boiler is fully on.
  2. Check the pressure gauge on the front of the boiler. If it reads below 1 bar, top it up using the filling loop as shown in the manual, then stop.
  3. Press and hold the reset button (the spanner or reset symbol on the display) for a few seconds to restart the boiler once, and check the condensate pipe is not frozen or blocked. If the code returns, call a Gas Safe registered engineer.

Parts commonly replaced

  • Fan assembly
  • Ionisation (flame sensing) electrode
  • Gas valve
  • Condensate trap
  • Control PCB

Related codes

Full explanation for FA
FC

Your boiler has shut itself down as a safety precaution because its burner or fan isn't working correctly, so it may not be providing heating or hot water until a qualified engineer checks it.

High Engineer only £150-450

What to check first

  1. Check the pressure gauge on the front of the boiler. It should read between 1 and 1.5 bar when cold; if it is below 1 bar, top it up using the filling loop as shown in the manual, then stop.
  2. Turn the boiler off at its power switch, wait 30 seconds, then switch it back on and press the reset button once, following the manual.
  3. Check that the condensate pipe running from the boiler outside is not blocked or frozen, and that no debris is visible around the flue outlet. If the boiler still shows FC, call a Gas Safe registered engineer and do not try to open the burner or fan.

Parts commonly replaced

  • Combustion fan assembly
  • Burner gasket
  • Burner gauze
  • Fan control PCB (control unit)

Related codes

Full explanation for FC
Fd

Your boiler has shut itself down as a safety precaution because its burner appears to be blocked or not working properly, so it may not be heating your home or water until it is checked.

High Engineer only £150-400

What to check first

  1. Check that the boiler has not lost pressure: the pressure gauge should read between 1 and 1.5 bar when the system is cold. Top it up using the filling loop only if the manual says to.
  2. Make sure the flue terminal outside the property is clear of leaves, snow, nests or other debris, and that nothing is blocking the air vents around the boiler.
  3. Turn the boiler off at its power switch, wait 10 minutes, then switch it back on to try a reset. If the fault returns, do not keep resetting it, as repeated resets can cause further problems. Call a Gas Safe registered engineer.

Parts commonly replaced

  • Burner control unit
  • Ionisation electrode
  • Burner gasket
  • Fan assembly
  • Gas valve

Related codes

Full explanation for Fd
Showing 21–21 of 21
FF

Your boiler has shut itself down as a safety precaution because its burner is not working properly, so it is likely not producing heat or hot water until it is checked.

High Engineer only £150-400

What to check first

  1. Check the boiler pressure gauge. If it reads below about 1 bar, top it up using the filling loop as shown in your manual, then stop.
  2. Press the reset button on the front of the boiler once, wait a few minutes, and see whether the boiler restarts.
  3. If the fault code returns or the boiler will not restart, do not keep resetting it. Turn off the boiler and call a Gas Safe registered engineer.

Parts commonly replaced

  • Burner gasket
  • Ignition electrode
  • Ionisation electrode
  • Fan assembly
  • Gas valve
  • Burner control unit

Related codes

Full explanation for FF