Viessmann
The Viessmann Vitocal 150-A is a monobloc air-source heat pump using R290 refrigerant, offering 10 to 16 kilowatt outputs and flow temperatures up to 70 degrees Celsius.
The Viessmann Vitocal 150-A is a high-temperature monobloc air-source heat pump designed for the UK retrofit and new-build market. Utilizing R290 natural refrigerant with a GWP of 0.02, it delivers flow temperatures up to 70°C, making it suitable for properties where traditional radiator systems are retained. Available in 10kW, 13kW, and 16kW outputs across single and three-phase variants, this inverter-driven unit achieves an ErP rating of A+++ at 35°C flow temperatures.
Stick a QR tag on the case, scan it on every service and give your customer a permanent, shareable service history they can pull up from any phone.
Permanent, shareable service history
One QR scan on the boiler surfaces every previous fault, part change and visit — no paperwork to dig out.
Free AI fault diagnostics, built in
Every tag you fit unlocks the AI diagnostic tool for that exact model — paste a fault code, get a ranked cause list.
Your name on the boiler forever
When the next service or breakdown comes around the homeowner scans and sees your number first.
First 12 BoilerTags are free
Tag every install and service you do from now on — the subscription only kicks in once you scale past your first dozen.
Diagnosing a fault on a Viessmann AWO-M-E-AC 151.A13 right now?
Try the free AI fault diagnostics tool — no signup needed.
Full technical specifications extracted from the manufacturer brochure. Empty sections are hidden.
The Viessmann Vitocal 150-A represents a significant shift in monobloc design, specifically engineered to replace fossil fuel boilers without requiring extensive emitter upgrades. Central to its performance is the use of R290 (propane), a refrigerant with an exceptionally low Global Warming Potential of 0.02. This allows the system to reach 70°C flow temperatures even when outdoor temperatures drop, maintaining operational capability down to -20°C.
Technically, the range is divided into 230V (AWO-M) and 400V (AWO) variants. The 10kW model provides a nominal capacity of 7.3kW at A7/W35, with a COP of 5.0. Efficiency remains high across the range, with a SCOP of 4.825 at 35°C and 3.7 at 55°C. These figures translate to an ErP rating of A+++ for low-temperature applications and A++ for medium-temperature use. The inverter-driven compressor ensures that the heat pump modulates its output to match the building load, reducing energy consumption and wear on components.
Installation requires consideration of the unit's physical footprint and weight. The outdoor unit stands 1382mm high and 1144mm wide, weighing 191kg, necessitating a stable, level base. Hydraulic connections use 28mm pipework to accommodate the minimum required flow rate of 16.67 litres per minute. The indoor unit is relatively compact at 920mm high and 450mm wide, housing the EHCU electronics module and providing the interface for the ViCare and Vitoguide control systems.
For service engineers, the Vitocal 150-A includes an integrated commissioning assistant. Maintenance intervals are set at 12 months, focusing on the hydraulic circuit pressure, expansion vessel pre-charge, and cleaning the evaporator fins. The system utilizes a 2kg charge of R290, classified as A3 (highly flammable), which dictates specific safety clearances: 200mm behind the unit and 1000mm at the front for service access. Troubleshooting is facilitated through a comprehensive fault code library. Common issues such as F.74 (low hydraulic pressure) or F.865 (high pressure fault) are clearly defined, often relating to air in the secondary circuit or pump blockages. By maintaining the minimum flow rates and ensuring the secondary circuit is correctly vented via the quick-action air vent valve, engineers can ensure long-term reliability.
Every fault code listed in the manufacturer brochure, with likely causes and engineer actions. Each code has a permalink — paste a URL like https://www.boilertag.com/heat-pumps/viessmann/awo-m-e-ac-151-a13#fault-f.1 to jump straight to the entry.
| Code | Meaning | Details |
|---|---|---|
| F.1Lockout | Lead break, flow temperature sensor Show causes & actionsLead break, flow temperature sensor, secondary circuit / heating/cooling circuit 1 Likely causes
Engineer action Check resistance value (NTC 10 kΩ) at connection X4.1/X4.2 of the EHCU electronics module. Replace sensor if required. | Details |
| F.2Lockout | Short circuit, flow temperature sensor Show causes & actionsShort circuit, flow temperature sensor, secondary circuit / heating/cooling circuit 1 Likely causes
Engineer action Check resistance value (NTC 10 kΩ) at connection X4.1/X4.2 of the EHCU electronics module. Replace sensor if required. | Details |
| F.3 | Lead break, secondary circuit return temperature sensor Show causes & actionsLead break, secondary circuit return temperature sensor Likely causes
Engineer action Check resistance value (NTC 10 kΩ) at connection X4.3/X4.4 of the EHCU electronics module. Replace sensor if required. | Details |
| F.4 | Short circuit, secondary circuit return temperature sensor Show causes & actionsShort circuit, secondary circuit return temperature sensor Likely causes
Engineer action Check resistance value (NTC 10 kΩ) at connection X4.3/X4.4 of the EHCU electronics module. Replace sensor if required. | Details |
| F.7 | Lead break, cylinder temperature sensor Show causes & actionsLead break, cylinder temperature sensor Likely causes
Engineer action Check resistance value (NTC 10 kΩ). Replace sensor if required. | Details |
| F.8 | Short circuit, cylinder temperature sensor Show causes & actionsShort circuit, cylinder temperature sensor Likely causes
Engineer action Check resistance value (NTC 10 kΩ). Replace sensor if required. | Details |
| F.13 | Lead break, outside temperature sensor Show causes & actionsLead break, outside temperature sensor Likely causes
Engineer action Check resistance value (NTC 10 kΩ). Replace sensor if required. | Details |
| F.14 | Short circuit, outside temperature sensor Show causes & actionsShort circuit, outside temperature sensor Likely causes
Engineer action Check resistance value (NTC 10 kΩ). Replace sensor if required. | Details |
| F.74Lockout | Hydraulic system pressure too low Show causes & actionsHydraulic system pressure too low Likely causes
Engineer action Top up with water. Vent the system. Check system pressure sensor with external pressure gauge. Check the pre-charge pressure of the expansion vessel. | Details |
| F.75Lockout | No flow in the secondary circuit Show causes & actionsNo flow in the secondary circuit, or flow sensor faulty Likely causes
Engineer action Check secondary pump/heating circuit pump. Replace if required. Check flow sensor. Replace flow sensor if required. | Details |
| F.87 | Safety valve opened Show causes & actionsThe safety valve in the indoor unit has opened. Likely causes
Engineer action Reduce the system pressure. | Details |
| F.155Lockout | Refrigerant circuit locked Show causes & actionsThe refrigerant circuit is locked due to electronic expansion valve 1 fault. Likely causes
Engineer action Check electronic expansion valve 1. Replace expansion valve if required. | Details |
| F.827 | Instantaneous heating water heater will not start Show causes & actionsHigh limit safety cut-out has responded. Likely causes
Engineer action Reset the high limit safety cut-out. Check instantaneous heating water heater. Replace if required. Safeguard the minimum flow rate. | Details |
| F.865Lockout | High pressure fault Show causes & actionsRefrigerant circuit off due to high pressure fault. Likely causes
Engineer action Vent the secondary circuit. Check the system pressure. Check secondary pump and heating circuit pumps. Flush heating circuits. Replace sensor if required. | Details |
| F.866Lockout | Low pressure fault Show causes & actionsRefrigerant circuit off due to low pressure fault. Likely causes
Engineer action Check amount of refrigerant. Top up refrigerant if required. Clean the evaporator. Check fans. Remove blockages. | Details |
Patterns that group across the manufacturer's fault-code table. Each entry links to the full code listing further down the page.
Engineer: Check resistance value (NTC 10 kΩ) at connection X4.1/X4.2 of the EHCU electronics module. Replace sensor if required.
Triggered by fault code F.1.
Engineer: Check resistance value (NTC 10 kΩ) at connection X4.1/X4.2 of the EHCU electronics module. Replace sensor if required.
Triggered by fault code F.2.
Engineer: Top up with water. Vent the system. Check system pressure sensor with external pressure gauge. Check the pre-charge pressure of the expansion vessel.
Triggered by fault code F.74.
Common questions from engineers and homeowners about the Viessmann AWO-M-E-AC 151.A13.
We hold the Viessmann AWO-M-E-AC 151.A13 manual — and every other UK boiler and heat pump brochure. Sign up and pull any model up from your phone, on the job.
Sign up to access brochuresTag it before you leave. Next scan shows every service, fault and part change — and the AI diagnostic tool is free on every tag you fit.
Specifications on this page are extracted from the manufacturer brochure. Always cross-check against the latest datasheet before commissioning or quoting. Last updated 30 April 2026.
Engineer: Check secondary pump/heating circuit pump. Replace if required. Check flow sensor. Replace flow sensor if required.
Triggered by fault code F.75.
Engineer: Check electronic expansion valve 1. Replace expansion valve if required.
Triggered by fault code F.155.