A practical guide to getting the most from your Samsung EHS heat pump. This covers the why and how of key settings — not just what they do, but how to set them up for comfort and efficiency.
Every 1°C reduction in flow temperature improves COP by ~2–3%
Lower flow temperatures are the single biggest lever for heat pump efficiency. The settings below help you achieve the lowest comfortable flow temperature.
Samsung calls weather compensation “Water Law”. It automatically adjusts your flow temperature based on outdoor air temperature — sending hotter water to your emitters when it’s cold outside, and cooler water when it’s mild. This is controlled by FSV settings 201* to 203*.
The curve is defined by two points: a cold outdoor temperature paired with a high flow temperature, and a warm outdoor temperature paired with a low flow temperature. The system interpolates linearly between them.
The chart below shows typical water law curves for underfloor heating (UFH) and radiators. As outdoor temperature rises, the target flow temperature drops — saving energy in mild weather.
At −10°C outdoor → 40°C flow
At 15°C outdoor → 25°C flow
At −10°C outdoor → 50°C flow
At 15°C outdoor → 35°C flow
Many installers accidentally reverse the water law values — setting the high flow temperature against the warm outdoor temperature and vice versa. The result: lukewarm radiators in cold weather and unnecessarily hot water on mild days. If your system feels backwards, check that the high flow temp is paired with the cold outdoor temp (Point ②), and the low flow temp with the warm outdoor temp (Point ①).
The default Samsung water law curve has a minimum flow temperature of 37°C. This ensures radiators always feel warm to the touch, even in mild conditions. While this prevents complaints about “cold radiators”, it can reduce efficiency. If your home is well-insulated and you’re comfortable with radiators that are merely warm (not hot) in mild weather, you can lower the minimum to 25–30°C for better COP.
Accessing Service Mode: Hold the up + down arrows on the wired controller for 10 seconds, then enter password 0202. For the complete FSV reference, see the FSV Reference Guide.
| FSV | Name | Recommended | Why |
|---|---|---|---|
| #2091 | External Thermostat #1 | Setting 4 | Best pump cycling balance — prevents unwanted anti-frost cycles |
| #2092 | External Thermostat #2 | Setting 4 | Same as above for second zone (FCU/radiator) |
| #201*–203* | Water Law Settings | Match to heat loss | Ensures correct flow temps for your emitters and climate |
| #3023 | HP ON temp diff | 10°C+ | Fewer, longer DHW cycles are more efficient |
| #3025 | Max DHW operation time | 95 min | Gives the HP time to finish DHW before immersion fires |
| #3032 | Booster delay time | 60–90 min | Let the heat pump work before expensive immersion kicks in |
| #3041 | Samsung disinfection | Not Use (0) | Runs too often, wastes energy — use a weekly timer instead |
| #3021 | Max HP temp for DHW | 55°C (R32) | Maximum the heat pump can achieve with R32 refrigerant |
| #3022 | HP OFF temp diff | 0°C | Heat pump stops at the set temperature, no overshoot |
| #3083 | BSH energy metering | Actual kW rating | Ensures accurate energy monitoring on the controller display |
FSV #2091 and #2092 control how the water pump behaves when using a third-party thermostat (external room thermostat). The setting determines what happens during “thermo-off” periods — when the thermostat is satisfied and the compressor stops.
Saves pump energy, but radiators cool down faster. Water stops circulating immediately when the compressor stops.
More even heat distribution — water keeps circulating even when the compressor cycles off, as long as the thermostat is calling for heat. Uses more pump energy.
The best balance for most installations. During thermo-off, the pump cycles with 7 minutes off and 3 minutes on. This prevents the system from triggering unwanted anti-frost (AF) protection cycles — which can extract heat from your DHW tank and waste energy — while still saving pump energy compared to Setting 3.
Note: These settings only apply when using external room thermostats. If you’re using the Samsung wired controller for room temperature control, leave #2091 and #2092 at 0.
Set FSV #3041 to Not Use (0). Samsung’s built-in legionella disinfection cycle runs too frequently and uses the immersion heater to heat the tank to 70°C — wasting significant energy.
Instead, use your immersion heater on a weekly timer (e.g., Tuesday 3am) with the thermostat set to 60°C or above. This gives the same legionella protection at a fraction of the energy cost. For vulnerable occupants, target 65°C.
Increase FSV #3023 (HP ON temp diff) to 10°C or higher. The default of 5°C causes the heat pump to start a DHW cycle whenever the tank drops just 5°C below the off point — leading to frequent, short, inefficient cycles. A larger hysteresis means fewer, longer cycles with better COP.
Increase FSV #3032 (booster delay) to 60–90 minutes. The default 20-minute delay is too short — the immersion heater fires before the heat pump has had a chance to finish heating DHW. The immersion uses roughly 3x the energy per kWh of heat delivered compared to the heat pump.
Tip: Ensure the booster delay (#3032) is shorter than the max DHW operation time (#3025). Setting #3025 to 95 minutes gives the heat pump maximum working time.
The DHW tank temperature sensor must be fully inserted into the middle pocket of the cylinder and secured in place. A sensor that has slipped out or is poorly positioned will give inaccurate readings — causing the heat pump to over- or under-heat the tank, and potentially triggering E919 legionella failure errors.
Quiet mode reduces compressor and fan speed on the outdoor unit to lower noise levels. There are 4 levels (0–3), with level 3 being the quietest — reducing noise by up to 30% (down to 35 dBA on HT Quiet models).
Quiet mode is configured via the outdoor unit LED display, not the indoor control panel. Set the four display segments to:
0 / 3 / 0 / xwhere x = quiet level (0–3)
At lower outdoor temperatures the heat pump needs to work harder. Restricting its output with quiet mode in cold weather can paradoxically increase both noise and energy consumption — the compressor runs longer at suboptimal efficiency trying to meet demand. Quiet mode is most effective in mild conditions where the unit has spare capacity.
These are two different processes that are often confused. Both involve the outdoor unit, but they serve different purposes and behave very differently.
Tip: If your DHW tank temperature drops significantly overnight in cold weather despite no hot water usage, frost prevention is the likely cause. Using FSV 2091/2092 Setting 4 (the 7/3 pump cycling) helps minimise the heat extracted from the tank during these protection cycles.
The table below gives recommended flow temperatures for common emitter types. Lower flow temperatures mean higher COP — so always aim for the lowest temperature that maintains comfort.
| Emitter Type | Design Flow Temp | Weather Comp Range | Notes |
|---|---|---|---|
| Underfloor Heating | 35–40°C | 25–40°C | Never exceed 45°C |
| Oversized Radiators | 35–45°C | 30–45°C | Best for COP |
| Standard Radiators | 45–55°C | 35–55°C | Set max to your design temp |
| Fan Coil Units | 35–45°C | 30–45°C | Fan compensates for lower temps |
This guide covers the most impactful settings. For every FSV code with defaults, ranges, and detailed notes, see the full reference.
View FSV Reference GuideImportant notes