Viessmann F2 fault codewhat it means and how to fix it
The temperature limiter has tripped because the boiler got too hot. Water is not carrying heat away and it should stay off until that is resolved.
Stop — this needs an engineer
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What are the radiators doing when it trips?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
Nothing heats up at all
No flow at all. The exchanger is taking full burner output with nowhere to send it.
Turn the boiler off and leave it off until it has been looked at.
There is gurgling or banging in the pipework
Air in the system, or water boiling locally in the exchanger. Both stop proper circulation.
Do not keep resetting. Mention the noise — it points straight at air or flow.
Some radiators heat, others stay cold
Partial circulation. A seized zone valve, a badly balanced system, or localised sludge.
Ask for the system to be balanced and the valves checked at the same visit.
What F2 means
F2 is a temperature limiter lockout on the Vitodens range. The limiter operates when flow temperature exceeds its fixed threshold and the fault latches so the boiler cannot restart unattended. On a modulating boiler, overheating means insufficient flow rather than excessive firing: the burner output is controlled, so if the exchanger reaches the limit it is because too little water is passing through it. Pump failure, air in the primary circuit, sludge and closed valves all present the same way. The reason this matters is the cost of the component being protected — a stainless heat exchanger is the single most expensive part in the appliance.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Pump not circulating | Failed, seized, or running too slowly for the system. | Common |
| Air in the primary circuit | Frequently after work on the system. Air prevents the pump moving water. | Common |
| Restricted flow from sludge | Cold-bottomed radiators are the visible symptom of the same restriction inside the boiler. | Occasional |
| Failed temperature limiter | The limiter reports an overheat that is not occurring. Diagnosed by measurement. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£150–£1,300
Time on site
2 hours
Call-out and venting £90–£140. Pump £280–£450. System clean £400–£700. Heat exchanger £700–£1,300.
Typical UK prices including parts and labour, updated August 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.
Central heating circulating pump
CH-PUMP-15-60£90–£180Plumbing merchant
Price checked 5 August 2026
Magnetic system filter, 22mm
MAG-22£65–£120Plumbing merchant
Price checked 5 August 2026
What other owners found
Nobody has shared what worked for them on this code yet. If you have had it, you would be the first — and it genuinely helps the next person.
Related Viessmann fault codes
- E3Get it checkedThe flow temperature sensor is reading outside its valid range. Usually the sensor rather than a genuine overtemperature.Related: overheat and circulation
- E9 219Stop — call an engineerThe boiler has overheated and the safety thermostat has tripped. Water is not carrying heat away from the exchanger, and it should not be run until that is fixed.Related: overheat and circulation
- L1Get it checkedThe boiler is not seeing enough water flow through it to run safely, so it has stopped. Usually a pump, an air lock, or a blocked filter.Related: overheat and circulation
- E02Get it checkedThe overheat thermostat has tripped. Almost always this means water is not moving through the appliance properly rather than that it is running too hot.Related: overheat and circulation
- F.20Stop — call an engineerThe overheat thermostat has tripped because the boiler got too hot. It has shut down to protect itself and it should not be restarted repeatedly.Related: overheat and circulation
- A02Get it checkedThe safety limit thermostat has tripped on overheat. In practice this nearly always means water has stopped circulating properly.Related: overheat and circulation
Related guides
Common questions about Viessmann F2
Can I keep resetting it to get heat tonight?
It is a false economy. Each cycle you force runs a stainless heat exchanger without adequate flow, and that part costs more than most repairs on the appliance. One reset to confirm the fault repeats is reasonable; beyond that you are gambling.
Why does it only trip on heating and not hot water?
The hot water circuit takes a different path through the appliance. If it works and heating does not, that narrows the fault to the heating side or the diverter valve, which is genuinely useful information for the engineer.
How much will this cost?
A pump is £280 to £450. Venting an air lock is usually within a call-out. A system clean is £400 to £700. A heat exchanger, if it has already been damaged, is £700 to £1,300.
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
- Interviews with working engineers
Checked by Technical reviewer (Gas Safe registration to be displayed on appointment) on 5 August 2026.