Viessmann F2 fault codewhat it means and how to fix it
The temperature limiter has responded — the boiler water got hot enough to trip the safety chain. Viessmann want the fill level, pump and limiter checked before any reset.
Stop — this needs an engineer
Get a Gas Safe registered engineer to look at your Viessmann F2
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What F2 means
F2 is "Burner in a fault state — Temperature limiter has responded" on every two-character Vitodens control unit including the WB1A, and it is the same row on the 050-W BPJD and the 111-W B1LA to B1LD. The temperature limiter is the mechanical high-limit thermostat in the safety chain, independent of the boiler water temperature sensor the control unit normally steers by; when it opens, the burner control unit locks out. Viessmann's measures are, in order, "Check heating system fill level. Check circulation pump. Vent the system. Check the temperature limiter and connecting leads. Press Reset." — a sequence that assumes the water stopped moving before it assumes the limiter is faulty, which is the right order, because a limiter that trips on a stagnant heat exchanger has done its job.
The WB1A service instructions add a useful test: if the burner control unit cannot be reset after a fault shutdown although the boiler water temperature is below approximately 75 °C, check the temperature limiter. For the householder, the operating instructions allow one reset on the unit's own control once the boiler has cooled (rotary selector to RESET under two seconds on WB1B/WB1C/B1HA, "R" for two seconds on B1HC, Reset key on WB1A, MODE and OK on BPJD), and they allow checking the pressure gauge and bleeding radiators if there is air in the system. A repeat F2 is a circulation problem or a failed limiter, and Viessmann say to call the contractor rather than reset again. The Vitotronic-controlled 200-W, 222-F and 242-F keep F2 with the same measures and "Press reset button R"; the 2015 B2HA edition words the cause as "Boiler water temperature sensor has responded", because on that unit the electronic high limit is a second boiler water sensor rather than a separate limiter. On the 2020-on numeric-table units the equivalent rows are F.62 (high limit safety cut-out has responded) and F.345 (temperature limiter has responded, re-enabled automatically once the appliance has cooled).
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Low system fill level | Not enough water in the primary circuit to carry heat away, so the heat exchanger overshoots. First in Viessmann's list. The B1HC operating instructions give 0.8 bar as the minimum pressure. | Common |
| Circulation pump not running or seized | A stuck or failed internal pump leaves the heat exchanger with standing water that heats past the limit within seconds of the burner firing. | Common |
| Air in the heat exchanger | An air lock does the same as a stopped pump locally. "Vent the system" is the third measure. | Occasional |
| Temperature limiter or its leads | A limiter that has drifted or a broken lead opens the chain with the water cool. The WB1A test — cannot reset below about 75 °C — points here. | Occasional |
| Scaled or blocked heat exchanger | Restricted waterways in an older Inox-Radial heat exchanger reduce flow through the hottest part. A repeat F2 with a good pump and a full system. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£70–£300
Time on site
1h 30m
A limiter and leads within a visit at the low end; a circulation pump at the high end. Filling and venting a system that was simply low costs a call-out.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Viessmann temperature limiter (safety chain high-limit thermostat)
£20–£50Authorised Viessmann parts distributor
Price checked 28 September 2026
Viessmann boiler water temperature sensor (NTC 10 kΩ)
£15–£45Authorised Viessmann parts distributor
Price checked 28 September 2026
Viessmann internal circulation pump
£150–£300Authorised Viessmann parts distributor
Price checked 28 September 2026
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Related Viessmann fault codes
- F.62Stop — call an engineerThe high limit safety cut-out has tripped on a 2020-on Vitodens: the boiler water got too hot and the burner is locked out. A Gas Safe engineer checks circulation, fill level and diverter valve.Related: overheat and circulation
- E3Stop — call an engineerA fault in the safety chain — the temperature limiter circuit has opened or its wiring has failed. Not a sensor fault; a Gas Safe engineer checks the limiter and control unit.Related: overheat and circulation
- F1Stop — call an engineerMaximum flue gas temperature exceeded. The flue gas sensor has seen the heat exchanger run too hot, almost always because water is not moving through it. Lockout; engineer.Related: overheat and circulation
- F.75Get it checkedNo flow rate detected through a 2020-on Vitodens. Viessmann start with top up and vent; if it recurs the engineer checks the boiler isolating valves, flow sensor and pump.Related: overheat and circulation
- F.63Stop — call an engineerThe flue gas temperature limiter has tripped on a 2020-on Vitodens and the burner is locked out. Reset only once the flue has cooled; the cause is a circulation check for a Gas Safe engineer.Related: overheat and circulation
- F.89Get it checkedThe internal circulation pump of a 2020-on Vitodens is blocked (F.89), reporting an electrical fault (F.799) or running dry (F.982). No heating or hot water until it is freed or replaced by an engineer.Related: overheat and circulation
Own a Viessmann boiler? Save it and its codes come first next time.
Related guides
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.