Samsung calls the cylinder immersion heater the booster heater, or BSH. It heats your hot water. It is not the backup heater, or BUH, used for the heating circuit.
For normal hot-water use, choose the mode on the controller. If the outdoor unit has failed, a separate emergency-hot-water function can use the immersion alone. The wiring-centre switch procedure below is for an installer, not a homeowner removing an electrical cover.
Which Samsung controls does this cover?
The normal button route is for the MWR-WW10N colour controller. The emergency switch instructions cover the matching MIM-E03CN / MIM-E03EN control kits. Check the kit label, not just whether the outdoor unit is called Gen 5, 6 or 7.
- Samsung colour-controller manual: hot-water modes
- Samsung CN/EN control-kit manual: DIP-switch functions
- Samsung 2026 controller manual: emergency hot water, printed page 55
Older monochrome controllers and the old MIM-E03A kit have different controls. Do not apply the numbered-switch instructions below to them.
Economic, Standard, Power and Forced: what is the difference?
| Mode | What it does |
|---|---|
| Economic | Uses the heat pump for the ordinary cylinder reheat, without immersion assistance. The programmed hygiene cycle is a separate function. |
| Standard | The heat pump starts first. Immersion assistance is available after the configured delay, if enabled and there is still demand. |
| Power | Allows immersion assistance without the Standard-mode delay. The immersion must be fitted, connected and enabled. |
| Forced | Prioritises hot-water production. It is not an immersion-only mode and is not the same as the emergency switch function. |
For an ordinary reheat, using the heat pump avoids unnecessary direct-electric heating. Keep the hot-water temperature and hygiene programme agreed at commissioning; changing an everyday mode is not a reason to disable the hygiene settings.
Mode behaviour: Samsung MWR-WW10N instructions, DHW section; earlier Samsung AN user manual, booster-heater variables. The actual delay is an installer setting, not a universal 30 minutes.
How to request hot water with immersion assistance
- Select DHW, not Zone. From the home screen, highlight the hot-water tile and open it with OK.
- Check the temperatures. Read the measured cylinder temperature and the target. A warm cylinder that has already reached its target does not need another reheat.
- Select the mode. Press OK to select the mode, then use the up/down arrows to choose Power when you need immersion-assisted reheating. Check the selected mode is shown on the display and DHW is on.
- Return to your usual mode afterwards. Do not leave a temporary change in place without meaning to. Check the next scheduled period too.
Do not assume Forced switches itself off after an hour. Samsung makes its timeout configurable; the manual's default does not automatically cancel it. If your installer has set a timed boost, follow that handover instruction.
The controller cannot enable hardware that was never fitted or connected. If Power is unavailable, ask the installer to check the immersion setup rather than trying random field settings.
How do I check whether the immersion is running?
Check Booster heater for the cylinder immersion. Back up heater is the separate heating-circuit heater; COMP operation is the compressor.
The display reports the control state. It does not prove that the element is drawing power or heating the water. Watch whether the cylinder temperature rises. If the controller requests the immersion but the temperature stays unchanged, an engineer needs to check the supply, thermostat, cut-out and element.
Installer checks for normal immersion operation
Record the existing field-setting values before changing anything. These are checks against the installed hardware, not a list for homeowners to copy.
| Setting | Check |
|---|---|
| 3011 | The configured DHW arrangement matches the installed cylinder and sensor. |
| 3031 | Booster-heater use is enabled where the connected immersion is intended to operate. |
| 3032 | The Standard-mode booster delay. The manuals reviewed give a 20-minute default, adjustable from 20 to 95 minutes. |
| 4022 | Backup/booster priority. Confirm the electrical design before permitting simultaneous heater operation. |
| 3051 / 3052 | Whether Forced mode has a timeout, and its duration. |
Match the manual to the equipment. A stored default is not evidence of the setting on this installation. Check the physical immersion supply and safety controls as well as the menu values.
Emergency hot water when the outdoor unit has failed
On the matching CN/EN kit, DIP switch 2 OFF enables emergency hot water using the cylinder booster heater. The controller manual specifies a 50°C default target. The immersion must already be installed, connected and correctly configured.
- Check the fault and backup arrangement. Establish that the cylinder and immersion are safe to operate. Do not energise an empty cylinder or equipment affected by a leak, electrical damage or overheating.
- Safely isolate and identify the switch bank. Match the control-kit label and SW03 markings to its manual. Photograph the original positions.
- Set switch 2 to OFF. Leave the other switches alone. Refit the enclosure before restoring power so the kit reads the changed position.
- Verify operation. Check the requested mode and tank temperature, prove that the immersion heats and stops correctly, and explain the temporary arrangement to the customer.
Emergency space heating uses a different function and requires a heating-circuit backup heater. Turning on the cylinder immersion does not heat the radiators or underfloor heating.
Emergency procedure: Samsung DB68-08470A-17, printed page 55, with switch identification from the CN/EN installation manual, page 42.
What can the homeowner check without opening anything?
- Record the error. Photograph the fault code and note when the hot water stopped.
- Check the normal controls. Is DHW on, is the schedule active and is the measured cylinder temperature below the target?
- Use only the backup control identified at handover. Some installations have a separate immersion timer or labelled boost switch. Others rely on the Samsung control kit. Follow the instructions for your arrangement; do not assume an isolator is a boost switch.
- Stop if a breaker trips or there are signs of damage. Do not keep resetting it. Contact the installer.
An immersion heats by direct electricity, so temporary backup changes the running cost. For illustration, a 3kW element running continuously for one hour uses 3kWh. The actual element rating and runtime determine the consumption.
We explain the cylinder arrangement in our heat-pump hot-water guide. For a flow fault on the heat-pump side, read what Samsung E911 means; an immersion can provide temporary hot water but does not repair that fault.
Samsung immersion-heater questions
Is the Samsung booster heater the immersion?
Yes, in the cylinder arrangement covered here. BSH is the cylinder booster or immersion heater. BUH is the separate heating-circuit backup heater.
Does Power mode use only the immersion?
No. It enables immersion assistance without the normal delay, where the heater is fitted and enabled. It is not the separate immersion-only emergency-hot-water function.
Will Forced mode switch itself off after one hour?
Not necessarily. Its timeout is configurable, and Samsung's documented default does not automatically cancel the mode. Follow the setting agreed at handover and restore your usual mode after a temporary change.
Can I get hot water if the outdoor unit has failed?
A correctly installed and configured immersion can provide emergency hot water. The route depends on whether it has independent controls or uses the Samsung control kit. Internal switch changes are installer-only work.
Does the cylinder immersion heat the radiators?
No. Emergency space heating requires a separate heating-circuit heater and a suitable system arrangement. The cylinder immersion heats domestic hot water.
Why is the booster shown on but the water stays cold?
The display reports the control state, not proof of electrical current or heat output. An engineer needs to check the supply, thermostat, thermal cut-out and element. Do not keep resetting a tripping breaker.
Not sure which backup arrangement you have?
Send us the fault code, a photo of the controller and the model label. We can identify the next step without asking you to open the wiring centre. Our heat-pump servicing and fault-finding service covers Lincoln and the surrounding area.
Use the instructions for the exact equipment and installation. This guide separates normal user controls from commissioning work inside electrical equipment.
