Viessmann F.980 fault codewhat it means and how to fix it
Hot water stopped on a 2020-on Vitodens because the boiler could not get enough flow through itself before (F.980) or during (F.981) cylinder heating. Heating carries on. Cylinder valves, air and pump for the engineer.
Take care
Get a Gas Safe registered engineer to look at your Viessmann F.980
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What F.980 means
F.980 and F.981 belong to the way these boilers protect themselves when heating a hot water cylinder. Viessmann's function description explains it: before DHW heating the internal flow rate is monitored, and if the threshold is not reached the diverter valve returns to the heating position for five minutes, then tries again; after four failed attempts, about twenty minutes, F.980 is output and DHW heating is blocked for the period set in parameter 1087.0, with heating still available. F.981 is the same logic applied while cylinder heating is under way — flow drops below the threshold, the valve returns to heating for five minutes, and after four failures the fault is shown. The rows list the causes together: "Shut-off or too much constriction. Scaling or sludge. Incorrect hydraulic configuration. Circulation pump faulty, air in the heating circuit. System pressure unstable or too low." On the B1GA and 050-W B0HA/B0KA the same numbers read simply "Water flow rate below minimum level".
The measures are a checklist for the installer as much as the repairer: every cylinder shut-off device fully open, the hydraulic scheme set correctly in the commissioning assistant, the system fully vented (Viessmann's venting programme can be run again from the service menu), the quick-action air vents on the appliance side permanently open and not leaking, the set system pressure checked ("this fault is more likely if the system pressure is too low"), and the circulation pump. Two things matter to the householder. First, this is a hot-water fault on a boiler that is still heating the house, so it is not an emergency. Second, Viessmann say the blocking time "can be terminated by carrying out a mains reset. Switch the appliance off and on again at the appliance switch" — the one action available from outside the case. A boiler that needs that every day has a real flow problem. The two-character units have no equivalent row; their 52/5A is the combi's tap-flow turbine, a different device.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Air in the primary circuit | After filling or work, air pockets in the boiler or cylinder coil stall the flow the monitoring expects. Viessmann's venting programme and the quick-action vents are the remedy. | Common |
| Cylinder valve closed or restricted | A shut-off on the cylinder flow or return not fully open, or a constriction in the pipework. First measure in the row. | Common |
| Low or unstable system pressure | Named in the row as making the fault more likely. Often a flat expansion vessel behind it. | Occasional |
| Scale, sludge or a tired pump | A furred cylinder coil or a sludged circuit raises the resistance; a pump that cannot push through it fails the threshold. The expensive end. | Occasional |
| Hydraulic scheme set wrongly | A commissioning parameter that tells the boiler to expect a flow path it does not have. Rare after commissioning. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£0–£320
Time on site
1h 30m
A valve opened or a system vented is a short visit. A pump, or a cylinder coil descale, is the top figure.
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 internal circulation pump
£150–£300Authorised Viessmann parts distributor
Price checked 28 September 2026
Viessmann diaphragm expansion vessel (Vitodens internal)
£70–£200Authorised Viessmann parts distributor
Price checked 28 September 2026
Viessmann 3-way diverter valve (motor and cartridge)
£60–£180Authorised Viessmann parts distributor
Price checked 28 September 2026
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Related Viessmann fault codes
- F2Stop — call an engineerThe 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.Related: overheat and circulation
- 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
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.