F.1336 on a Viessmann One Base: Low pressure in refrigerant circuit
Short answer
On a Viessmann heat pump, F.1336 means: Low pressure in refrigerant circuit. The heat pump keeps running. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Low pressure in refrigerant circuit.
Part involved: Low pressure in refrigerant circuit.
When it shows: System characteristics:; Limited normal operation; High pressure and low pressure too low; Frost formation on the evaporator uneven; High temperatures in the compressor.
Likely causes:
- Refrigerant loss.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: Not stated per code in Viessmann document 6199893 GB 01/2026 (VSA00009).
Manual reset: User may acknowledge via HMI after noting the code (6249162 p.57); the message returns if the cause persists.
What you can check
- On the HMI, tap the message and "?" to read the system characteristics and Viessmann's user tips; note the code (e.g. F.xxx) and text for your contractor (operating instructions 6249162 p.57).
- Acknowledge the message once via the HMI; do not acknowledge fault messages several times in quick succession (6249162 p.58) - notify your contractor.
- Check the outdoor unit is not blocked by leaves, debris or snow.
What the engineer will check
- Check whether all Schrader valves on the low pressure and high pressure sides are open.
- Check the refrigerant circuit for leaks:.
- Check refrigerant lines for mechanical damage. Refrigerant lines must be connected free of load and torque stress.
- Check all fittings and solder joints.
- Check all heat exchangers.
- Check the 4-way diverter valve.
- Check expansion valves for ice and correct function.
- Check the compressor for damage and oil loss.
Who to ask for: Viessmann-trained heat pump engineer with F-gas certification and R290 (A3 flammable refrigerant) competence.
Certification: F-gas certificate (UK F-gas Regulations; EU 2015/2067 Cat. I cited by Viessmann) plus A3/R290 competence per EN 378-4 or IEC 60335-2-40 Annex HH (6202263 p.2).
What you might notice
Sources
- Service instructions for contractors: Heat pumps in monoblock design incl. hybrid – System configuration and diagnostics (Vitocal 150-A/151-A/250-A/252-A, IDU-A, AWMOF-151/251, AquaSnap 30AWH, BI-BLOC R290) (6199893 GB 01/2026) ↗ · 6199893 GB 01/2026 (VSA00009) · page 200 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026