Buderus Boiler Error Codes: 6A, 6C, 6L, 2F and A01

By Ray Bennett · Updated 17 October 2026 · 8 min read · Checked against the sources at the end

Buderus Boiler Error Codes: 6A, 6C, 6L, 2F and A01

Short answer

Buderus's GB142 manual calls 6A with 227 a missing flame signal after ignition, with lockout after four startup attempts. 6L with 229 means the signal failed during operation. 6C, 2F and A01 need their second number to identify the condition. These meanings belong to the GB142 with BC10 control.

Buderus boiler error codes make more sense when you keep both parts of the message. On the GB142, Buderus gives 6C with 228 a different meaning from 6C with 306, even though the first screen looks the same.

This guide covers Logamax plus GB142-24/30/45/60 with the BC10 basic controller and UBA 3 burner control. It also explains why the SSB85/120/160 LCD control needs a separate fault list. Start with the model on your paperwork or an accessible identification label.

Before you start

What to carry: a torch, a pen and the manual supplied with your boiler. Keep the cabinet closed; the useful owner checks here are at the display and outside the appliance.

Gas or electric? Buderus’s manuals here cover gas fired hot water boilers. An oil burner, electric boiler or a different Buderus control needs its own instructions.

Renting? Send the fault details to whoever arranges the heating repairs before authorising work.

Handle danger before looking up a code.
Overheating, or gas that will not shut off. Buderus’s GB142 user manual says to leave the pump’s electrical supply on and shut off the gas supply at a location outside the boiler. Arrange urgent service; do not try a power reset.

Smell gas? The same manual says not to light an appliance, touch an electrical switch or use a phone in the building. Leave and call the gas supplier from outside. Follow their instructions. If you cannot reach them, call the fire department.

A carbon monoxide alarm. CPSC says to move outside to fresh air, call emergency services and account for everyone. Stay out until responders permit you to return.

Leave internal work to the repairer. Buderus reserves GB142 installation, electrical work and maintenance for a trained service provider. Do not open gas connections, adjust combustion or bypass a safety control. Its user manual also says not to use a boiler that has been partly underwater until a technician inspects it and replaces the affected controls.

Get the second number from the GB142

The two example views belong together: 6C with 306. Buderus's GB142 chart distinguishes that fault from 6C with 228.

Check 1No parts to buy for this check

Use Service to read the complete fault

Buderus’s GB142 service manual says the Service button calls up the additional code when a fault is displayed. For example, the main code 6A pairs with 227.

Write down the model, both codes, whether they flash, and whether the boiler failed to start or stopped after heating. Include whether the rooms, the hot water tank, or both have gone cold.

Buderus distinguishes a flashing lockout from a steady blocking fault on this control. Its service instructions say a blocking fault can clear when its cause is corrected.

You do not need to enter chimney sweep mode or change installer settings to collect this information.

GB142 codes 6A, 6C and 6L

Buderus’s GB142 fault table uses ionization for the flame sensing signal. The timing of that signal separates these faults.

GB142 code pair	What Buderus’s chart means
6A with 227	No flame signal after ignition; locks out after four startup attempts
6C with 228	A flame signal measured before the burner starts
6C with 306	A flame signal measured after the burner shuts off
6L with 229	The flame signal fails during operation

Check 2No parts for an outside look; testing determines the repair

6A 227: check the air openings, then arrange diagnosis

Buderus’s GB142 user instructions say to keep air intake and outlet openings clear. Buderus also says not to store flammable materials or liquids near the boiler. Look at accessible openings from the ground for an obstruction, without dismantling a pipe or reaching into the boiler. Pass any blockage you cannot safely deal with to the repairer.

For 6A, Buderus’s service sequence checks the gas supply pressure, hot surface igniter, gas valve, air and gas mixture, flame sensing circuit and air and flue passages. That is why the code alone cannot tell you which part to order.

If yours lights and then loses the signal, Buderus’s chart places 6L with 229 in that running phase. The repairer will investigate the fuel supply and flame sensing system using its separate 6L sequence.

6C belongs with a technician. Buderus’s 228 branch checks the ionization electrode; its 306 branch checks for pressure at the burner after the heat request ends and can lead to gas valve replacement. Leave that diagnosis and restart to the repairer.

On the GB142, a missing signal at ignition, a lost signal while running and a signal at the wrong time are different faults.

GB142 code 2F: a temperature check

Buderus gives 2F two entries in its GB142 display table. Neither is simply a verdict that the pump has failed.

GB142 code pair	What Buderus’s chart means
2F with 260	No temperature rise after burner start, or the supply and safety sensors differ by more than 27 degrees F; listed as an operating code
2F with 271	The supply and safety sensors differ by more than 27 degrees F; listed as a blocking fault

Buderus marks 260 as visible only with the service tool. An owner seeing 2F may therefore have no second number available on the BC10; leave that field blank rather than guessing.

Check 3An outside observation first; circulation or sensor work if needed

Tell the repairer what the water side is doing

Buderus’s 2F service chart checks open service valves, system pressure, an open thermostatic valve, the supply and safety sensors, and the primary pump. Tell the repairer whether this started after plumbing work or closing radiator controls.

The GB142 user manual lets you cycle through the display with Service to see system pressure in psi. Record that reading with the fault details. Leave filling, bleeding and pump testing to someone familiar with your installation.

If 2F persists and the rooms remain cold, the related guide to boiler circulator pump problems explains the circulation side of the investigation. A sensor problem remains another possibility in Buderus’s chart.

GB142 A01: the number after it matters

Buderus lists these as system messages in the GB142 service manual. Keep A01 and the following number together; they point to different parts of the heating and hot water controls.

GB142 system code	What Buderus identifies
A01 with 800	Outdoor temperature sensor problem
A01 with 808	Hot water temperature sensor problem
A01 with 809	Hot water temperature sensor 2 problem
A01 with 810	Hot water remains cold while the system keeps trying to heat the tank
A01 with 811	Thermal disinfection was interrupted
A01 with 816	No communication with EMS, the boiler’s control communication system
A01 with 828	Water pressure sensor problem

For A01 with 810, Buderus’s checks include ongoing hot water draw or a leak, the tank sensor and its wiring, and the tank heating pump. Let the repairer know whether taps have been running or you have noticed a leak. For the wider tank problem, see an indirect water heater that is not heating.

SSB messages and the reset question

Check 4The message determines the service work

Use the SSB screen's own wording

Buderus’s SSB85/120/160 service manual shows an LCD panel with Menu, ESC, OK and Reset buttons. Its error table uses named messages and internal numbers, including these examples.

SSB85/120/160 message	Internal number	What Buderus means
Ignit Error	1	Three unsuccessful ignition attempts in a row
Flame Error 1	28	Flame detected before ignition
Overheat Error	70	Supply temperature exceeds the limit

These entries belong to the LCD control in that manual. Do not convert its internal number 1 into GB142 A01 or apply this list to an SSB255, 399, 512 or another SSB control.

Check 5A button press after correction; service for an unresolved fault

Reset only after dealing with the cause

For a flashing GB142 fault whose cause has been corrected, Buderus’s user instructions say to hold Reset for approximately five seconds. The BC10 shows rE while resetting.

For the SSB85/120/160 LCD control, Buderus says a lockout needs the Reset button after eliminating the cause. A blocking error returns to normal operation once its cause is eliminated, without pressing Reset.

After a restart, check that the rooms warm and the fault stays cleared. If it stays or returns, give the heating service company the record from check 1. Buderus’s GB142 user manual also warns about freezing during a shutdown; arrange protection for the system if repairs leave it without heat in freezing weather.

What each one takes

Finding	What the work involves
GB142 6A or 6L	Testing ignition, gas supply and flame sensing before choosing parts
GB142 6C	A technician investigating an unexpected flame signal
GB142 2F	Checking water flow, valves, pressure and temperature sensors
GB142 A01	Following the second number to the affected sensor, tank or communication circuit
SSB LCD fault	Diagnosis from that model’s named error and lockout or blocking table

Questions people ask

Is GB142 0H an error?

Buderus’s GB142 user manual lists 0H as ready for operation. If the house is cold while it stays there, see the thermostat and demand checks for a boiler not working.

What does 0A mean on a GB142?

Buderus says 0A means the burner is waiting and will restart automatically after 10 minutes. It belongs to the normal operating messages in the GB142 user manual.

What does H7 alternating with P mean?

Buderus’s GB142 user manual identifies H7 as low water pressure and the P value as the pressure in psi. It tells the owner to contact the installer. See boiler pressure problems if pressure keeps falling.

Are -H and =H faults on the GB142?

No. Buderus lists -H as space heating and =H as domestic hot water heating in its normal operating messages.

Does a clear display mean the GB142 needs no maintenance?

No. Buderus’s user instructions call for a trained service provider to check, clean and service the heating system annually. They also reserve periodic condensate collection and disposal system cleaning for a trained technician.

The other boiler guides: boiler not working, boiler keeps turning off, and boiler pressure.

Sources: Buderus Logamax plus GB142-24/30/45/60 Servicing Instructions 7214 9400 (11/2011), pp. 4, 20 to 26, 49, 65 to 77; GB142 User's Instructions 7215 0300 (02/2008), pp. 2, 6 to 7, 18 to 23; Bosch Home Comfort US Condensing Gas Boilers FAQ, GB142 6A section; Buderus SSB85/120/160 Service Manual 6720866940 (2017/11), pp. 1, 13, 32 to 34; CPSC Carbon Monoxide Questions and Answers.