The Vitodens 100-W and 200-W, Viessmann's wall-hung residential boilers, show faults differently. A Vitodens 100-W (B1HA, or the B1KA combi) flashes a fault symbol with the code beside it, and an R on the display means the burner is locked. A Vitodens 200-W with the Vitotronic control shows the word Fault with a flashing red indicator; pressing OK gives the cause in plain words with its code, such as an outside temperature sensor with 18 beside it. The 200-W also keeps the ten most recent faults in a fault history, including ones that have already cleared, which is how a technician can see what happened overnight.
One reset is reasonable. Viessmann's operating instructions say to hold R for about two seconds, and in the same breath warn against resetting a burner fault several times in quick succession. If the same burner fault returns, the boiler needs a TSSA-licensed gas technician, because the real causes are not visible from the front panel: worn ignition and ionization electrodes, a blocked condensate trap, low gas pressure, or combustion that has drifted out of range. Viessmann's start-up guide calls for a combustion analysis once faults have been cleared, and that takes an analyzer.
Code tables are not the same across the range, so match the model before trusting any list. F4 is the no-flame fault on the Vitodens 100-W; the current 200-W (B2HA) reports the same problem as EE or EF. FC means a fan control fault on the 100-W and a gas valve or blocked vent on the 200-W. Older Vitodens generations and floor-standing Viessmann boilers have their own tables again.
This page was built from Viessmann's current Canadian service instructions for the B1HA, B1KA and B2HA. The fault table in the service instructions that shipped with your boiler, and the rating plate inside the cover, overrule anything written here. Our Viessmann boiler repair page covers how we service these boilers, and you can send us the code and the model so the right parts come on the first trip.
Viessmann boiler codes, decoded
| Code | What it means | Safe? | Try first | When to call |
|---|---|---|---|---|
10 / 18 | Outdoor temperature sensor shorted (10) or its wire broken (18). The 100-W runs in constant mode; the 200-W heats as if it were 0°C outside. | keep running | Check that the outdoor sensor on the outside wall is intact and its cable has not been cut. | At your convenience. The house stays warm, but the boiler has stopped adjusting to the weather. |
30 / 38 | Boiler water temperature sensor shorted (30) or its wire broken (38). Burner blocked. | turn it off | Nothing at home. The burner will not fire without this sensor. | Same day in winter. There is no heat until the sensor or its lead is replaced. |
50 / 58 | Domestic hot water tank temperature sensor shorted (50) or its wire broken (58). No hot water heating; space heating carries on. | keep running | Leave the heating on. | Within a day or two, sooner if the indirect tank is your only hot water. |
51 / 59 | Outlet temperature sensor shorted (51) or its wire broken (59) on the 100-W combi. No hot water heating. | keep running | Leave the heating on. | Soon. The radiators still work, the taps will not get hot. |
0A | Vitodens 100-W: the CO limiter (if installed) has responded to a high CO concentration, or the gas pressure switch (if installed) has responded to low gas pressure. Burner blocked. | call now | If a carbon monoxide alarm is sounding, get everyone outside and call 911. Do not reset the boiler. | Immediately. Both causes are gas-side and need a licensed technician. |
0b | Vitodens 100-W: low water, or a defective pump or flow switch. Burner blocked. | turn it off | Read the pressure gauge and look for water under the boiler or at radiator valves. | If pressure is low or keeps dropping. A boiler that loses water has a leak to find. |
0C | Vitodens 100-W: mains voltage too low. Burner blocked until the supply recovers. | keep running | Check whether other things in the house are dimming. A neighbourhood brownout clears without any repair. | If it recurs with normal house power. The supply to the boiler needs checking. |
A9 | Vitodens 100-W: communication fault with an OpenTherm control. The boiler keeps regulating without it. | keep running | Check the batteries or power of the room control. | If the room control stays disconnected. Wiring or the OpenTherm device needs replacing. |
b0 / b8 | Flue gas temperature sensor shorted (b0) or its wire broken (b8). Burner blocked. | turn it off | Nothing at home. | Same day in winter. The boiler will not fire with its flue sensor out of circuit. |
F1 | Maximum flue gas temperature exceeded. Burner in fault mode. | turn it off | Check the pressure gauge. Let the boiler cool before the one reset. | If it returns. Fill level, trapped air and the circulation pump are Viessmann's listed checks. |
F2 | Fixed high limit tripped. The boiler water got too hot because heat is not being carried away. Burner in fault mode. | turn it off | Check the pressure gauge and make sure radiator and zone valves are open. Reset once. | If F2 repeats. Low water, air in the system or a failed circulation pump is behind it. |
F3 | Flame signal already present at burner start, before the gas valve should have opened. Burner in fault mode. | call now | Leave the boiler off. | Right away. The ionization electrode circuit or the gas valve has to be checked before it runs again. |
F4 | Vitodens 100-W: no flame signal. The burner tried to light and the control never saw flame. | turn it off | Confirm the gas is on and the vent terminations outside are clear of ice. Reset once. | If it locks out again. Electrodes, ionization current, gas pressure and the condensate drain all get checked. |
EE / EF | Vitodens 200-W (B2HA): flame signal missing or too weak at burner start (EE), or flame lost immediately after it formed (EF). | turn it off | Same checks as F4: gas on, vent clear, one reset. | If it repeats. On the 200-W, flue gas recirculating into the air intake is on the list of causes. |
F8 | The combination gas valve closes too late. Burner in fault mode. | call now | Leave the boiler off and do not reset it. | Right away. A gas valve that is slow to close is a safety fault. |
F9 | Blower (fan) speed too low at burner start. Burner in fault mode. | turn it off | One reset. | If it returns. The fan, its cables, its power supply and the fan control are tested in turn. |
FA | Blower not at standstill when it should be stopped. Burner in fault mode. | turn it off | One reset. | If it returns. The fan or the control that drives it is misbehaving. |
The codes that usually mean a real repair
F4, or EE and EF on the 200-W — ignition and flame sensing
Most no-flame lockouts on a Vitodens come down to the parts that light and prove the flame, or to water sitting where it should not: the ignition and ionization electrodes wear and drift out of position, and a condensate trap packed with debris backs water up into the burner area. Clearing a condensate drain or replacing a trap is $150–$350. Electrodes, gaskets and the combustion analysis that follows are quoted in writing after the $90–$150 diagnostic, which is folded into the repair. Annual service catches most of this before it becomes a lockout.
F2, F1 or 0b — water is not moving
A high-limit trip is a circulation problem until proven otherwise: the system is low on water, there is air trapped at the boiler, or the circulation pump has stopped. Topping up pressure is not a repair if the gauge keeps falling, because the water is going somewhere. We do not publish a flat price for hydronic parts: the pump model and the piping around it set the cost, so you get a written quote. See boiler circulator pump replacement for what the job involves.
F9 or FA — the combustion fan
These two codes point at the fan assembly, its wiring harness or the control unit that drives it. The fan on a Vitodens is a Viessmann part matched to the boiler's serial number, which is why the price is quoted and not guessed. On a boiler past fifteen years, ask for the repair price beside a replacement price before approving it; whether to repair or replace a boiler sets out how we weigh that.
Licensed technicians, a written price before the repair, no overtime charges.
Common questions
How do I reset a Viessmann Vitodens boiler?
On a Vitodens 100-W, a flashing fault symbol with R on the display means the burner is locked. Press and hold R for about two seconds, and the normal display returns if the fault is gone. On a 200-W, press the R reset button and acknowledge the message on screen. If the code is back the same day, stop resetting and write it down for the technician.
Why does my Viessmann lock out only on the coldest nights?
Look outside first. Viessmann's operating instructions warn that in sustained cold below -18°C the vent termination can be severely blocked by icicles and frost, and the control shuts the boiler down when the intake or vent is blocked. Knock the ice away gently if you can reach it safely, then switch the boiler off and on. Lockouts that follow the cold with a clear vent call for a gas pressure and combustion check.
My boiler shows 50 or 58 but the radiators are hot. Can it wait?
For a day or two, yes. Those codes mean the control has lost the sensor on the domestic hot water tank, so it stops heating the tank while space heating carries on. Nothing unsafe is happening. The practical limit is how long the household can go without hot water, since the tank will cool and stay cool until the sensor or its lead is replaced.
Who is allowed to repair a Viessmann gas boiler in Ontario?
Gas-side work has to be done by a technician holding a TSSA gas licence, working to the CSA B149.1 gas code. That includes the gas valve, burner, electrodes and venting, and it is why Viessmann's manuals are addressed to a licensed heating contractor. A homeowner can read the code, check the pressure gauge, clear ice from the vent and press reset once. Opening the sealed combustion chamber is not on that list.
Are Viessmann fault codes the same as codes on other condensing boilers?
No. The parts are similar across brands, but each manufacturer numbers its faults its own way, so F2 on a Viessmann tells you nothing about F2 on another make. If your boiler is a different brand, use that brand's table, such as the Navien combi boiler code guide. For a Viessmann that keeps faulting, our boiler repair service starts with the fault history and a combustion test.