Viessmann F.87 fault codewhat it means and how to fix it
System pressure too high on a numeric-display Vitodens. Burner and internal pump stop. Usually an overfilled system or a flat expansion vessel; the contractor checks vessel charge and the pressure sensor.
Take care
Get a Gas Safe registered engineer to look at your Viessmann F.87
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.87 means
F.87 is the high-pressure counterpart of F.74 on the 2020-on Vitodens 100-W, 111-W and 050-W. Its row: "Burner locked out. Internal pump off. No central heating and no DHW heating — System pressure too high — Check the system pressure and correct if necessary. Check pre-charge pressure of diaphragm expansion vessel. Check whether BDF valves are open. Check the system pressure sensor with an external pressure gauge." The BDF valves are the boiler's own flow and return isolators; if one has been left closed after work the pump sees a dead end and pressure spikes as the water heats. Like F.74 the row carries no reset instruction — the boiler is being held by its sensor and is expected to release when the pressure falls back into range as the water cools.
What makes F.87 a contractor code rather than a householder one is that lowering pressure means letting water out, and Viessmann's operating instructions give the user no procedure for that; they only say what to do when pressure is low. A filling loop left cracked open is the innocent version and shows itself immediately, but the persistent version is an expansion vessel that has lost its air charge: pressure then rises steeply as the water expands, the relief valve may dribble outside, and the boiler swings between F.87 hot and F.74 cold. Recharging or replacing the vessel is the repair. A pressure sensor reading high with an external gauge disagreeing is the last item in Viessmann's list and the least common.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Expansion vessel flat | Nowhere for the expanding water to go, so pressure climbs as the boiler heats and falls as it cools. The second measure in the row, and the usual finding when F.87 recurs. | Common |
| Overfilled or filling loop left open | Topped up to 2 bar or more cold, or a filling loop valve not fully closed so mains pressure keeps feeding the system. Shows at once rather than developing. | Common |
| BDF valve closed | A boiler isolating valve left shut after a service or repair. Viessmann name it: "Check whether BDF valves are open." | Occasional |
| Pressure sensor reading high | Checked against an external gauge, as the row instructs. Replaced if it disagrees. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£60–£220
Time on site
1 hour
Recharging an expansion vessel is a short visit; replacing the internal vessel on a Vitodens is the high end.
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 water pressure sensor
£30–£75Authorised Viessmann parts distributor
Price checked 28 September 2026
Viessmann diaphragm expansion vessel (Vitodens internal)
£70–£200Authorised Viessmann parts distributor
Price checked 28 September 2026
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Related Viessmann fault codes
- F.74Get it checkedSystem pressure too low on a 2020-on Vitodens with the numeric display. The burner and pump stop until the pressure is back. Viessmann tell the householder to top up below 1.0 bar.Related: water pressure
- E6Get it checkedSystem water pressure too low — a code only on the WB1A, early WB1B and Vitotronic 200-W. Viessmann's measure is to top up with water; later 100-W units show the flashing pressure instead.Related: water pressure
- F.471Get it checkedThe system pressure sensor is missing, open-circuit or shorted on a 2020-on Vitodens, so the boiler will not run at all. A sensor and lead check for the engineer.Related: water pressure
- F4Stop — call an engineerNo flame signal was detected during burner start on any two-character Vitodens, so the burner has locked out. Reset once; if it returns, call a Gas Safe engineer.Related: same brand
- F.65Stop — call an engineerNo flame signal at burner start on a 2020-on Vitodens — the numeric table's equivalent of F4. Burner locked out. Check the gas is on, reset once; if it returns, call a Gas Safe engineer.Related: same brand
- EAStop — call an engineerA Lambda Pro combustion-controller code on Vitotronic-controlled 200-W, 222-F and 242-F boilers: the ionisation current during calibration was outside the permissible range or implausibly different from last time. Lockout; engineer.Related: same brand
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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.