Viessmann heat pump error codes

17 codes that Viessmann UK publishes for its heat pumps, each with what it means, the likely cause, what you can safely check and when to call an installer. Tap your code:

Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work. Anything else is for the heat-pump installer or the maker’s service engineer: in the UK and EU only an F-gas certified technician may open the refrigerant circuit. Codes that need one are marked Installer.

Read this first

Some Viessmann Vitocal heat pumps are run by a Siemens Albatros2 controller (RVS61), and Viessmann UK publishes that controller’s user manual with its Vitocal 200-A documents. On those units a fault shows as a number and a short text on the operator unit — 10:Outside sensor, 118:Water pressure too low, 222:Hi-press on HP op. The manual is written for the installer and gives no owner checks, but it says what each code does to the heat pump: some lock it out until someone makes a manual reset, some clear themselves when the cause goes. Models differ: newer Vitocal ranges such as the 150-A and 250-A have their own controls and manuals, not checked here — your model’s manual is the authority.

`118` Water pressure too low

What it means: The water pressure measured by the pressure sensor fell below the critical minimum (0.5 bar is the factory setting), so the controller switched the heat pump off. The error clears itself once the pressure rises again past the limit. Above that, between the critical and the normal minimum (0.8 bar by default), the controller only gives a maintenance message, 5:Water pressure too low.
Likely cause: Low water pressure in the heating circuit.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer: refilling and finding where the water went is theirs to do with this manual.

Source: Viessmann UK, Siemens Albatros2 Series F heat pump controller RVS61.843 user manual (CE1U2355en_058, edition 1.4, 2022-04-12; Viessmann 6155607 GB), published as the Vitocal 200-A controller user manual: 6.34.1 Error codes and the settings it refers to Checked 2026-10-13.

`117` Water pressure too high

What it means: The water pressure measured by the pressure sensor went above the set maximum (3 bar by default). The error clears when the pressure drops back below the limit.
Likely cause: Water pressure above the maximum the installer set.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`222` `223` `224` High-pressure switch tripped

What it means: The refrigerant high-pressure switch (E10) tripped. If the flow and return water were both below 20 °C, the manual reads it as no water flow on the heating side: the heat pump locks out at once, as 223 if heating was starting or 224 if hot-water charging was starting. If both were above 20 °C, the heat pump restarts after its minimum off time, and only locks out with 222 when the switch trips more often than the set number of times. A locked-out heat pump restarts only after a reset.
Likely cause: Too little water flowing through the heat pump, or repeated over-pressure in the refrigerant circuit.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer: a reset without finding the cause just repeats the lockout.

`225` Low-pressure switch tripped

What it means: The refrigerant low-pressure switch (E9) tripped. The heat pump stops, restarts after its minimum off time, and locks out with 225 if it trips more often than the set number within the set period; then only a manual reset restarts it. The manual’s table marks this one for customer service.
Likely cause: Low refrigerant pressure; the manual names the switch, not the cause.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer or Viessmann service: anything in the refrigerant circuit needs an F-gas certified technician.

`226` Compressor overload

What it means: The overload protection of compressor 1 (input E11) acted (227 is compressor 2 on two-stage units). The heat pump stops, the error must be acknowledged by hand, and the manual’s table marks it for customer service.
Likely cause: Compressor overload.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer or Viessmann service.

`201` Frost alarm

What it means: The water temperature at the heat pump’s flow sensor (B21) fell below the frost alarm level, so the heat pump shut down to stop the system freezing. It runs again only after a reset. The manual gives the reason the check exists: a reversing valve that seizes, for example after defrosting.
Likely cause: Water at the heat pump flow too cold — a stuck reversing valve is the case the manual describes.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`247` Defrost fault

What it means: A defrost could not be finished normally even after the set number of repeat attempts, so the heat pump switched off. It resumes only after a manual reset.
Likely cause: Defrosting failing repeatedly; the manual names the event, not the cause.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer: the reset and the cause are theirs.

`134` Common fault heat pump

What it means: A heat pump fault signalled on the controller’s common-fault input (E20). The heat pump stops and the error must be acknowledged by hand; the number tells you only that the heat pump itself reported a fault.
Likely cause: A fault reported by the heat pump unit; the controller does not know which.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`10` Outside sensor

What it means: A fault in the outside temperature sensor (B9). The manual’s table lets the heat pump keep running with this error, which clears itself (no manual acknowledgement).
Likely cause: A faulty or disconnected outside sensor.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`33` `44` Heat pump flow or return sensor

What it means: A fault in the heat pump’s flow sensor (33, B21) or return sensor (44, B71). The table lets the heat pump keep running and needs no manual acknowledgement.
Likely cause: A faulty or disconnected water temperature sensor.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`121` Heating circuit 1 flow too cold

What it means: The flow temperature of heating circuit 1 stayed below its setpoint for longer than the time the installer set for this alarm (122 and 371 are circuits 2 and 3).
Likely cause: The heat pump not reaching the flow temperature the circuit asks for.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`127` Legionella temperature not reached

What it means: During the anti-legionella function, the hot-water circulation pipe did not reach the required temperature within 48 hours.
Likely cause: The circulation pipe staying too cool during the legionella run.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`105` Maintenance message

What it means: A maintenance message is pending — for example a service interval that has run out. It is a message, not a stoppage.
Likely cause: A maintenance interval or condition set by the installer.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Book the service the message asks for with your installer.

`385` Mains undervoltage

What it means: The controller detected undervoltage on the mains supply (input E21). The manual’s table lets the heat pump keep running, but the error has to be acknowledged by hand.
Likely cause: Supply voltage too low.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

A code that is not listed here

The Albatros2 table lists about 150 error numbers, many of them set-up errors (“BX1 No function”, address collisions) that an installer sees at commissioning. For a number not listed here, note it with its text and call your installer. The table also gives each error a priority: from priority 5 up, the controller sends an alarm for remote monitoring and sets its alarm relay, so a heat pump with remote monitoring may already have told your installer.

We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.

Source

Every code on this page comes from this page, published by Viessmann UK and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.

Viessmann UK: Siemens Albatros2 Series F heat pump controller RVS61.843 user manual (CE1U2355en_058, edition 1.4, 2022-04-12; Viessmann 6155607 GB), published as the Vitocal 200-A controller user manual: 6.34.1 Error codes and the settings it refers to Checked 2026-10-13.

Viessmann heat pump error codes

Read this first

118 Water pressure too low

117 Water pressure too high

222 223 224 High-pressure switch tripped

225 Low-pressure switch tripped

226 Compressor overload

201 Frost alarm

247 Defrost fault

134 Common fault heat pump

10 Outside sensor

33 44 Heat pump flow or return sensor

121 Heating circuit 1 flow too cold

127 Legionella temperature not reached

105 Maintenance message

385 Mains undervoltage