Viessmann F.95 fault codewhat it means and how to fix it
The OpenTherm room controller a 2020-on Vitodens expects is not connected (F.95) or connected but not configured (F.738). On a 100-W or 111-W the burner will not run; the 050-W carries on.
Take care
Get a Gas Safe registered engineer to look at your Viessmann F.95
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.
Which Vitodens shows F.95?
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.
Which Vitodens shows F.95?
The row says "Burner not operational": the boiler will not heat until the OpenTherm controller is back on the bus or the installer changes C.7. Not a lockout — nothing to reset — but no heat either.
Check the room controller is powered and connected as its own instructions describe. If it is, or if you have removed it, call your heating contractor to check the connection or re-parameterise the boiler.
Which Vitodens shows F.95?
The row says "Normal operation": the boiler has fallen back to its own control and keeps heating. The message tells you the room controller is not being heard.
Check the controller's power and connection at your convenience; ask the contractor to look at the next visit if it persists.
What F.95 means
These boilers can be told at commissioning that an OpenTherm room controller is their source of heat demand, and F.95 is what happens when that controller then goes missing. The row on the 100-W B1HF/B1KF, B1HG/B1KG and 111-W B1LF/B1LG reads "Burner not operational — OpenTherm remote control not connected — Check connection to the OpenTherm remote control. If OpenTherm is not required, set C.7 in the commissioning assistant to a value not equal to 14." On the B1GA and the 050-W B0HA/B0KA the same cause carries "Normal operation" as its system characteristic — the boiler falls back and keeps running. That is the same code with a different consequence by control unit, and it is the reason to read the type designation before deciding how urgent F.95 is. F.738 is the mirror image, "Normal operation — OpenTherm remote control connected but not configured — Set C.7 in the commissioning assistant to a value of 14": a controller is wired in but the boiler has not been told to listen to it.
The usual cause is mundane: a wireless OpenTherm thermostat's receiver unplugged, a controller with flat batteries that has dropped off the bus, or a two-core cable to a wired controller disturbed during decorating. Parameter C.7 is in the commissioning assistant and is the installer's to change, so a household that has removed an OpenTherm controller for good needs the contractor to re-parameterise the boiler rather than live with a code. Viessmann's operating instructions for the boiler say nothing about the controller beyond referring to its own instructions, so the householder steps are limited to checking the controller is powered and connected as its manual describes. On the two-character B1HC/B1KC the equivalent is A9, "Communication error with an OpenTherm device"; the Vitotronic 200-W has no OpenTherm row at all.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Controller unpowered or its receiver unplugged | Flat batteries in a wireless OpenTherm thermostat, or its receiver disconnected. The boiler loses the bus and shows F.95. | Common |
| OpenTherm cable disturbed | The two-core link between controller and boiler broken or loose at a terminal after decorating or other work. | Common |
| Controller removed but boiler still expects it | C.7 left at 14 after an OpenTherm controller was taken out. The boiler waits for a demand that will never come; the installer changes the parameter. | Occasional |
| Controller fitted but not configured (F.738) | The reverse: C.7 not set to 14 after an OpenTherm controller was added, so the boiler ignores it. Commissioning oversight. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£0–£120
Time on site
30 minutes
Batteries or a plug cost nothing. A visit to re-terminate a cable or change C.7 is the paid outcome.
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 programming unit (display and keypad, HMI)
£120–£280Authorised Viessmann parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Viessmann fault codes
- A9Usually simple to fixOn a 100-W, 111-W or 050-W, A9 is a communication error with the OpenTherm room controller: the boiler carries on heating without it. On a 242-F it means the internal pump is blocked.Related: controls and communication
- F.102Usually simple to fixThe WiFi communication module of a 2020-on Vitodens has lost contact: F.102 on the fault list, E10 or E12 during connection. Heating is unaffected; only the ViCare app link is down.Related: controls and communication
- 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.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: 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
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.