On a touchscreen IBC (the V-10 controller fitted to SL G3 and VX boilers) the strip across the home screen is the whole readout. IBC calls it the boiler status bar: green with the time in it when all is well, yellow for a warning, red for an alarm, with the text of the fault inside the bar. If more than one alarm is active, the text rotates slowly through them, so watch it for a full minute before deciding there is only one problem. The wording in the table below is copied from IBC's own troubleshooting pages.
The stored history is three taps in: from the Main Menu choose Diagnostics, then Advanced Diagnostics, then Error Log. Each record carries the date, the time, the error class and a snapshot of the boiler's operating readings at that moment, and the controller keeps a practically unlimited number of them. The Clear Errors button sits on the same Advanced Diagnostics screen. Older SL boilers with the five-button keypad and text screen keep their error log under Diagnostics as well, and sort faults into soft errors that retry after five minutes and hard lockouts.
The HC and DC series are the exception: they flash E1 to E7 for warnings and plain numbers for faults, with a Reset button and a fault lamp, so do not read an SL message list against one of those. Codes and wording vary by model and controller software, and the manual for your model plus any label inside the cabinet win over this page. Our IBC boiler repair page covers the lines we service, the Viessmann code guide is the comparison if you are weighing brands, and the brands hub lists the rest.
IBC boiler codes, decoded
| Code | What it means | Safe? | Try first | When to call |
|---|---|---|---|---|
Error – Ignition Failure after 3 tries | IBC's Maximum Ignition Trials error. The boiler failed to light on three successive attempts, sits locked out for one hour, then repeats the three-try sequence. | turn it off | Check that the manual gas shutoff is open. IBC lists a closed valve or an unpurged gas line among the causes. | If it recurs, as the message itself says. Igniter lead, probe gap, spark module and grounding are tested in turn. |
Error – Water High-Limit Exceeded | Hi-limit cutoff. Water temperature passed the high limit and the boiler is in hard lockout. | turn it off | Make sure zone valves and radiator valves are open, and read the pressure gauge. | Same day. The limit is reset and tested by a technician, and the reason water stopped moving has to be found. |
Error - Low Water Cutoff | The safety and ignition module has detected a low water condition in the boiler. | turn it off | Look at system pressure and for water on the floor. Do not reset a boiler that may be dry. | Same day. IBC's own note is that air in the system is the typical trigger, so the loop is purged before the cutoff is reset. |
Error – Water High-Limit/LWCO | Combined message on SL boilers fitted with both a water high limit and a factory low water cutoff: water too hot or water level low. Hard lockout with a one-hour reset. | turn it off | Note whether it appeared right after the system was drained or bled. | If it returns after the hour. The cutoff module has its own reset button, and its probe is checked for corrosion. |
Error - Vessel/Vent High-Limit Exceeded | Vent temperature has tripped the vent limit switch, or the upper vessel high limit has tripped. The boiler is locked out and the screen adds a call-for-service line. | call now | Leave the boiler off. Do not reset it. | Immediately. Flue gas this hot means a fouled or blocked heat exchanger, and the venting must be inspected before it runs again. |
Error – Insufficient Air Flow | Not enough combustion air is proving. IBC classes it as a soft error that retries in five minutes. | turn it off | Clear snow, ice, leaves or a nest from the intake and exhaust outside. | If the outside pipes are clear. A blocked condensate trap, a fouled air-pressure line or the fan is next on IBC's list. |
Insufficient Water Pressure | The water pressure sensor is reading below what the controller needs to fire. | turn it off | Compare the on-screen pressure with the mechanical gauge on the piping if there is one. | If both read low, or if they disagree. A leak, a flat expansion tank or the sensor plug on the board. |
Error - Max. Inlet/Outlet Sensor Temp. Exceeded | An inlet or outlet water temperature signal is outside the acceptable range. The screen itself prompts you to check water flow. | turn it off | Feel whether the pipes leaving the boiler are scorching while the radiators stay cool. | Book a repair. A failed circulator, air locking the loop or a faulty temperature sensor. |
Loop/Indoor Sensor | A loop or indoor temperature sensor input is missing or out of range. | keep running | Nothing at home. | At a convenient time. IBC's first check is that the sensor plug is fully seated in the back of the controller board. |
Aux. Interlock 1 or 2 | An auxiliary interlock terminal is open: either its jumper lead is loose or an external safety device wired to it is in alarm. | turn it off | Think about what else is wired to the boiler, such as a floor-heat limit or a condensate pump switch, and check that device. | If you cannot find the external device at fault. |
Unknown Error | The controller has a fault input it cannot classify. IBC groups it with the unseated sensor plug. | turn it off | Switch power off for a minute and back on, once. | If it comes back. The connections on the rear of the controller board are reseated and the sensors tested. |
Blank screen, fan running | Display dark while the fan runs. IBC's older manual flags possible power-surge damage; the current guidance is to check the transformer and inspect the circuit board. | turn it off | Check the breaker and the service switch, nothing more. | Book a repair. IBC's rule is that a defective control module is replaced, never repaired. |
Fault 4 (HC / DC) | No flame signal. Ignition failed or flame was not detected. | turn it off | Confirm the gas valve is open, then press Reset once. | If it faults again. IBC lists gas pressure, the ignition gap, a blocked condensate drain and grounding. |
Fault 5 (HC / DC) | Poor flame signal: the flame is there but weak or unstable. | turn it off | Check that the vent termination is not drawing its own exhaust back in past a snowbank or a fence. | Book a repair. Condensate drainage, ignitor and cable, gas valve adjustment and flue gas recirculation are checked. |
Fault 1 (HC / DC) | Temperature too high. Water in the heat exchanger has passed the safe limit. | turn it off | Open any radiator valves that were shut for the season. | Same day. Air in the system, a pump that is not running or too little flow. |
Fault 8 (HC / DC) | Incorrect fan speed. The fan is not reaching or holding the speed the controller asked for. | turn it off | Nothing at home. | Book a repair. The fan is checked for rubbing and bad wire contacts before it or the controller is replaced. |
E1 (HC / DC) | Warning: flue gas temperature approaching its limit. The boiler cuts back and clears the warning itself when the reading falls. | keep running | Note how often it appears and whether the supply temperature has been turned up. | Soon if it is frequent. A heat exchanger that needs cleaning is the usual reason flue temperature climbs. |
LO / pressure P (HC / DC) | Boiler loop pressure too low. The display alternates the pressure reading with LO. IBC lists 4 psi as the minimum to ignite and 8 psi for full firing. | turn it off | Look for a leak and for water at the relief valve discharge. | If pressure will not stay up after the loop is refilled. |
The codes that usually mean a real repair
Ignition Failure after 3 tries: igniter, probe gap and condensate
Most recurring IBC ignition lockouts come down to three things: the igniter probe rods wear and the gap drifts outside IBC's 1/8 to 3/16 inch window, the ceramic insulator cracks so the spark tracks to ground, or condensate backs up from a blocked trap and wets the burner. Because the boiler retries every hour, it can limp along for days lighting on the second or third attempt before it quits entirely. A worn igniter is replaced, usually along with its lead, and combustion is rechecked. IBC boiler parts are not in our published price bands, so after a $90–$150 diagnostic, folded into the repair if you go ahead, you get the figure in writing.
Insufficient Air Flow or Vent High-Limit: trap, vent and intake
An IBC proves airflow with a pressure sensor, so anything that chokes the air path trips it: a condensate trap packed with sediment, a sagging vent run holding water, or frost closing down a side-wall termination when wind comes off Lake Ontario in a January thaw-and-freeze. The soft error retries every five minutes, which reads as a boiler that runs for a while and stops. Clearing a blocked condensate trap or drain is typically $150–$350. A vent high-limit trip is a different grade of problem and stays off until the heat exchanger and venting are inspected.
Low Water Cutoff or Max. Inlet/Outlet Temp: circulator and air
Both messages are about water, not fire: air collects at the top of the heat exchanger after a radiator is bled or a zone is drained, the cutoff probe sees air and trips, and the boiler locks out. A circulator that has seized over the summer gives the inlet/outlet temperature error on the first cold night because heat has nowhere to go. The repair is a proper purge, a new air vent or a pump, and occasionally an expansion tank. See boiler repair for how we quote hydronic work, or send us the message on your screen.
Licensed technicians, a written price before the repair, no overtime charges.
Common questions
Where is the error log on an IBC boiler?
On the touchscreen: Main Menu, Diagnostics, Advanced Diagnostics, Error Log. Each error type shows a View button if anything is stored against it, and the record includes the date, time and boiler readings. The log can be saved to a USB stick or SD card. On older keypad SL boilers the log is under Diagnostics, reached with the arrow keys.
How do I clear an error on an IBC touchscreen boiler?
Main Menu, Diagnostics, Advanced Diagnostics, Clear Errors, then Yes and OK. IBC prefers this to switching the power off because it is faster and makes the controller re-check every sensor. Clearing does not fix anything: if the fault is still present the red bar returns. Photograph the message and the Error Log before clearing so the history is not lost.
What is the difference between a warning and an error on an IBC boiler?
A warning turns the status bar yellow and the boiler carries on, sometimes at reduced output or after a short pause. An error turns it red and stops the burner. IBC splits errors again: minor ones purge, wait five minutes and resume; major ones are lockouts that IBC says must be checked and restarted by a service technician. Ignition failure sits between the two with its one-hour retry.
Why does my IBC boiler work for an hour and then stop again?
That pattern fits the ignition retry cycle. After three failed lights the boiler locks out for an hour, tries three more times, and may catch on one of them. It then heats until the next call, fails again and waits another hour. A house that drifts cold in the early morning and recovers by breakfast is usually on this cycle.
My IBC shows a number, not a message. Which list do I use?
You have an HC or DC model. E1 to E7 are warnings that flash only while the condition exists and clear themselves. Plain numbers with a flashing fault lamp are faults that need the Reset button after the cause is corrected: 4 is no flame signal, 5 is poor flame signal, 1 is temperature too high, 8 is fan speed.