Biasi Boiler Error Codes - How To Fix

If your Biasi boiler is showing an error code, the first step is working out whether it is a simple lockout or a fault that needs professional attention.

Some codes are linked to pressure or one-off ignition problems. Others point to issues with circulation, sensors, the fan, or the flue.

This guide covers the most useful Biasi boiler error codes for homeowners, what they usually mean, and what you can safely do next.

What do Biasi boiler error codes mean?

Biasi boiler error codes are there to show what type of fault the boiler has detected.

Some point to simple system issues, such as low pressure or a temporary ignition lockout.

Others relate to overheating, temperature sensors, circulation, the fan, or the flue. The code helps narrow the problem down, but it does not always tell you the exact repair needed.

That is why error codes are useful for diagnosis, but not a substitute for proper fault-finding when the same problem keeps coming back.

Can you reset a Biasi boiler?

Sometimes, yes.

A reset may clear a temporary lockout, especially after a failed ignition attempt or one-off interruption. If your boiler manual allows it, trying one reset is usually reasonable.

But a reset is not a repair. If the same code comes back, the underlying fault is still there. Repeatedly resetting the boiler without fixing the cause is rarely helpful and can delay the right repair.

As a simple rule:

• try one reset if the manual allows it

• do not keep resetting the boiler over and over

• if the code returns, get it checked

Which Biasi boiler faults are most important?

From a homeowner point of view, the most useful way to read Biasi error codes is by fault type.

Some codes are more likely to be reset-type lockouts. Others usually point to faults that need an engineer. The most common and useful groups are:

• ignition and lockout faults

• overheating and circulation faults

• sensor faults

• fan and flue faults

Ignition and lockout codes

These are some of the most common codes homeowners see because the boiler will often lock out when it cannot light safely.

ER 01 - ignition fault

ER 01 usually means the boiler has failed to ignite.

Possible causes include:

• interrupted gas supply

• ignition problems

• flame detection issues

• a temporary lockout after failed attempts to fire

You can usually try one reset. If the code clears and stays away, the issue may have been temporary. If it comes back, it needs checking.

If you also suspect a gas supply problem, check whether other gas appliances in the home are working. If nothing gas-related is working, the issue may be wider than the boiler itself.

ER 03 - general lockout

ER 03 is often a more general lockout code.

This is less specific than some other Biasi faults, which means it is often a sign the boiler has shut down to protect itself rather than a code that points neatly to one single part.

If it appears once, a reset may be worth trying. If it returns, treat it as a fault that needs proper diagnosis.

Overheating and circulation codes

These codes are often linked to poor water flow through the boiler or heating system.

ER 02 - overheat or safety thermostat lockout

ER 02 usually means the boiler has overheated or the safety thermostat has stepped in.

This can be linked to:

• poor circulation

• pump issues

• trapped air

• sludge in the system

• low water pressure

A reset may clear the code once, but if the system is overheating again, the cause still needs attention. If radiators are not heating properly or the boiler keeps locking out, get it checked.

ER 04 - low flow or circulation issue

ER 04 usually points to poor water flow through the boiler.

This can mean:

• low system pressure

• poor circulation

• a pump issue

• restricted water flow through the boiler

Before calling for help, you can safely check the pressure gauge and see if the system pressure looks low. If it is low, repressurising may help. If the code comes back, there is likely to be a deeper issue.

ER 13 - large temperature difference

ER 13 usually means the boiler has detected too much of a difference between the flow and return temperatures.

This often points to a circulation problem rather than a simple electronic fault. Common causes include:

• poor water flow

• pump problems

• sludge or debris

• trapped air

• blockages in the system

This is one of the clearer signs that the wider heating system may be involved, not just the boiler itself.

ER 14 - pump fault

ER 14 usually points to a pump fault.

The pump is what moves heated water through the system. If it is not working properly, the boiler may struggle to circulate heat and can lock out to protect itself.

This is not a DIY repair. If your Biasi boiler is showing ER 14, it will usually need an engineer.

Sensor-related codes

These faults usually mean the boiler is not getting the temperature readings it expects.

ER 06 - central heating flow sensor fault

ER 06 usually points to a fault with the central heating flow temperature sensor.

If that sensor is faulty or sending the wrong reading, the boiler may struggle to control heating properly and can lock out.

A reset may clear the code briefly, but if the sensor or its wiring is faulty, the code will usually return.

ER 07 - hot water sensor fault

ER 07 usually points to a domestic hot water temperature sensor fault.

On a combi boiler, this can affect hot water performance as well as triggering the code on the screen. If the sensor is not reading properly, the boiler may struggle to regulate domestic hot water correctly.

This usually needs professional diagnosis.

ER 08 - external sensor fault

ER 08 usually relates to an external temperature sensor fault, where one is fitted.

Not every system will use this setup, but if yours does, the code may point to a fault with an external sensor or weather-compensation control. It is not always an urgent fault, but it still needs checking if it persists.

ER 09 - flue temperature sensor fault

ER 09 usually means there is a problem with the flue temperature sensor.

This matters because the boiler uses flue-related readings as part of safe operation. If the sensor is faulty, the boiler may lock out or stop working properly.

This is best treated as an engineer issue rather than a homeowner fix.

ER 12 - return sensor fault

ER 12 usually points to a fault with the return-side heating temperature sensor.

This is similar in principle to ER 06, but on the return side of the system. If the boiler cannot trust the temperature readings, it may not control the heating properly.

As with other sensor faults, it usually needs professional diagnosis if it does not clear.

Fan and flue faults

These are some of the most important codes to take seriously because they relate to combustion safety and the removal of gases.

ER 05 - fan fault

ER 05 usually points to a fan fault.

The fan is a key safety part because it helps the boiler remove combustion gases safely. If the fan is not working as it should, the boiler should not continue to operate normally.

Do not try to inspect the fan yourself. If your boiler is showing ER 05, it needs an engineer.

ER 10 - flue overheat or flue-related lockout

ER 10 usually means the boiler has locked out because of a flue-related fault or overheating around the flue side of operation.

This can suggest:

• a flue issue

• overheating combustion gases

• poor airflow

• a sensor problem related to flue performance

Because this touches on safe combustion and flue operation, it is not something to guess at. A reset may clear it once, but if it comes back, stop there and get it checked.

What can you safely check yourself?

If your Biasi boiler is showing an error code, keep your checks simple and external.

You can safely check:

• whether the pressure is too low

• whether radiator valves are open

• whether radiators are heating unevenly

• whether there are visible leaks

• whether the code returns straight after a reset

• whether other gas appliances are working, if the code is ignition-related

You should not:

• remove the casing

• test internal wiring or sensors

• try to inspect the fan, flue components, or burner yourself

• keep resetting the boiler repeatedly if the same code returns

When should you call an engineer?

You should call an engineer if:

• the same code comes back after a reset

• the boiler keeps locking out

• the fault is linked to ignition, the fan, the flue, or temperature sensors

• the heating or hot water is not working properly

• the pressure keeps dropping

• there are multiple fault codes appearing

In general, the more often the code returns, the less likely it is to be a one-off issue.

How much does it cost to fix a Biasi boiler fault?

The cost depends on what is actually causing the code.

A straightforward issue, such as a minor pressure-related problem or a simple component fault, will usually cost less than a wider circulation issue involving the pump, blocked system water, or more complex diagnostics.

That is why error codes are best treated as a diagnosis-first problem rather than something with one fixed repair cost.

Do Biasi boiler error codes mean you need a new boiler?

Not usually.

A single error code does not normally mean you need a replacement. In many cases, the issue can be repaired.

Replacement becomes more likely if:

• the boiler is older

• faults are becoming more frequent

• repair costs are building up

• reliability is getting worse

• there are wider circulation or system issues as well

If the same or similar codes keep coming back, it may be time to look at the bigger picture rather than just the latest fault.

What to do if your Biasi boiler shows an error code

Start with the safe basics. Check the system pressure, try one reset if appropriate, and look for obvious external issues such as leaks or poor radiator performance.

If the code clears and does not return, the fault may have been temporary. If the same code comes back, especially if it relates to ignition, circulation, sensors, the fan, or the flue, the boiler usually needs proper diagnosis.

Repeated lockouts are a sign that the fault itself has not been fixed. If your Biasi boiler is older and error codes are becoming more frequent, it may also be worth thinking about whether repair is still the best long-term option.

Where replacement makes more sense, iHeat offers fixed online quotes for new combi boilers, with finance options available and installation dates shown during the quote journey.