HVAC Classroom: Q&A Compilation on Electric Wall-Mounted Boilers

概要： Electric Wall-Mounted Boiler Q&A Compilation For the initial installation of an electric wall-mounted boiler, personnel must first read the <<Quick Installation Manual for Electric Wall-Mounted Boilers>> before installing the unit. Installation must be performed by an electrician with professional electrical qualifications and a plumber who is familiar with hydronic systems.

Electric Wall-Mounted Boiler Q&A Compilation

1. What is the difference between an electric wall-mounted boiler and a gas wall-mounted boiler?

One uses gas, the other uses electricity; electricity has a higher thermal efficiency than gas—essentially 100%.

2. Installation of an electric wall-mounted boiler?

The installer must read the <<Electric Wall-Mounted Boiler Quick Training Manual>> before installing the unit.

Installation must be performed by an electrician with professional electrical qualifications and a plumber or other installer familiar with plumbing.

3. Is the after-sales service for electric wall-mounted boilers complicated?

After-sales service is straightforward: the machine consists of three main components—circuit board, water pump, and heater—so it can be repaired by a qualified electrician. Additionally, we provide relevant training materials and technical guidance, so there’s no need for your company to send personnel locally for training.

4. Differences in operating costs between electric wall-mounted boilers and gas wall-mounted boilers

Compared with gas, 8 kWh of electricity is equivalent to 1 cubic meter of gas. For example, a house that requires 500 cubic meters of gas for one heating season would need 4,000 kWh of electricity if using electric heating equipment to achieve the same heating effect.

5. With such a high power rating, is an electric wall-mounted boiler safe?

Electrical safety is independent of power and depends only on current and voltage; accordingly, it poses the same safety level as a light bulb. Moreover, electric wall-mounted boilers are equipped with leakage protection, overpressure protection, overtemperature protection, and dry‑burn protection, so safety is fully assured.

6. Must an electric wall-mounted boiler always be connected to an air switch with leakage protection?

Electric wall-mounted boilers must be connected to a residual current device (RCD)-protected circuit breaker.

7. Can the machine be used without a ground wire? If I want to make my own ground wire, how should I do it?

The machine must be grounded.

If you want to build your own grounding system: drive a 1-meter-long copper pipe 1.5 meters into the ground, and connect the pipe to the grounding wire at the junction point.

8. Can an electric wall-mounted boiler operate continuously for 24 hours?

(1) Electric wall-mounted boilers can operate 24 hours a day.

(2) If an electric wall-mounted boiler runs continuously for 24 hours, it indicates that the selected capacity is too small, which is detrimental to heat retention and energy efficiency.

(3) It is recommended to replace the wall-mounted boiler with a higher-capacity model, or to lower its set temperature, so that the boiler can heat up to the desired temperature and then switch to standby mode.

9. After a power outage, does the electric wall-mounted boiler retain its previous settings when restarted?

(1) Retain the existing settings, but you must press the power button again to turn the device on.

(2) When the device leaves the factory, the display board is shipped without a battery. For devices without a battery, the standard time must be reset after a power outage. For devices with a battery, the standard time does not need to be adjusted after a power outage. However, for devices with a battery, the battery should be replaced after two years of use to prevent leakage that could corrode the display board.

10. Can the device be installed outdoors? Is it dangerous if water gets on the device?

(1) The machine is designed for indoor use and must not be installed outdoors.

(2) Water entering the machine may cause a short circuit or electric leakage, which is very dangerous.

(3) If water has entered the machine, immediately disconnect the power supply (trip the circuit breaker). Have a qualified electrician open the machine cover and use a hair dryer to dry any water inside.

11. Can an electric wall-mounted boiler be used with a plug?

No, the largest domestic socket can only handle 16A of current and is rated for products up to 3kW.

12. During installation, can the product’s live and neutral wires be connected arbitrarily?

220V products should be wired according to the standard live and neutral connections to achieve optimal safety protection.

380V products must never be connected incorrectly.

13. What if the meter wiring cannot meet the product’s load requirements?

Unable to install this product

14. Conversion between floor area and power

Based on gross floor area, the typical allocation is 900,000 to 1.1 million per square meter; for example, for a 100-square-meter space, calculate at 1 million per square meter.

100㎡*100w=10KW. So when selecting a product, choose one with a capacity of at least 10KW.

15. Should I choose a product with lower wattage to save more electricity?

That’s incorrect; in fact, higher power often leads to greater energy efficiency because higher‑power products spend more time in standby, resulting in lower actual energy consumption.

If the power rating is too low, the machine will run continuously, resulting in higher actual energy consumption and failing to achieve optimal performance.

16. What are the operating costs of an electric wall-mounted boiler?

The operating cost of an electric wall-mounted boiler is generally calculated based on the unit running at full load for 6–8 hours. That is: power × hours × electricity rate = operating cost.

(If the customer keeps emphasizing that the operating costs are higher than those of gas, don’t dwell on this issue. Instead, point out that they don’t have natural gas; if they did, they would use gas. To reduce costs, they should improve insulation, lower the operating temperature, and implement staged, timed controls.)

17. Ratio of electrical power to gas power.

A ratio of 0.8:1 means that 16 kW of electricity delivers the same performance as 20 kW of gas.

18. Could we use a smaller wire?

No, it must be equal to or greater than the machine’s power requirement. Additionally, many wires sold in various places are not standard national‑standard cables, so in actual use they are generally oversized. Using undersized wiring is strictly prohibited.

19. Currently Produced Models and Specifications

Power ranges from 5 kW to 24 kW, with products available at 220 V and 380 V; future models will cover the 32–100 kW range.

20. Product warranty period — For product quality issues, the entire unit is covered for 3 years, and the heater is covered for a lifetime.

21. Product Configuration

Danish Grundfos water pumps, Taiwan Songchuan relays, enclosed structure, oxygen-free copper heat exchanger, and special alloy heating wires.

22. What is the machine’s heating method?

Our company’s electric wall-mounted boiler uses a resistance-type plate heat exchanger heater. The key features of this heating technology are electrical–water separation, high thermal efficiency, stable operation, and a long service life.

23. How does it differ from other electric heating wall-mounted boilers on the market?

Resistive plate heat exchanger heating: high cost, high thermal efficiency, stable operation, long service life.

Electromagnetic heating: high cost, low thermal efficiency (because electrical energy is converted to magnetic energy and then to thermal energy; the more conversion steps, the lower the thermal efficiency), electromagnetic pollution during operation, and a short service life.

Quartz tube heating: low cost, but thermal efficiency degrades over time (because the carbon film coating on the quartz tube tends to volatilize when heated, reducing efficiency), and it has a short service life.

Cup-type or tank-type heating: low cost, prone to scaling (scale easily forms on the inner walls of the water tank and heating elements, posing a risk of electrical leakage), and short service life.

24. Is your equipment variable-frequency? Is variable-frequency better?

Our heating equipment is not inverter‑type, and inverter‑based constant‑temperature technology is not suitable for it. If applied, the system would run continuously around the clock, which would actually increase energy consumption and shorten the equipment’s service life.

25. What are the standard cross-sectional areas for electrical wires?

Wire cross-sectional area series: 0.5, 0.75, 1.0, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185

26. What specifications are available for air circuit breakers?

Air switch ratings: 6, 10, 16, 20, 25, 32, 40, 63, 80, 100, 125, 160, 200, 250, 400, 630, 800, 1000 A

27. What is the temperature difference of the machine’s return water, and what is the pump’s operating status?

During normal operation, the return water temperature difference is 20°C, and the pump runs continuously. If the customer has special requirements, they may request adjustments to the return water temperature difference and the pump’s on/off temperature setpoints. (To ensure optimal product performance, adjustments are discouraged whenever possible.)

28. Does the machine have an antifreeze function?

The machine has an antifreeze function: it automatically operates when the temperature drops below 7°C and stops when it rises to 10°C.

29. Meaning of Product Model Numbers

D L N 0 1 0 8 15 11 30 01

D stands for electric wall-mounted boiler.

L stands for two-phase electrical products, and S stands for three-phase electrical products.

N stands for single use; L stands for dual use.

01 represents the product design serial number.

0 8 represents the product’s rated power

15 11 30 represents year month day

01 indicates the production batch number for this batch.

29. Several operating modes of the machine (see the manual for details)

Gear mode

Segmented Timing Mode

60-degree temperature-limited mode

Smart Mode

"Manual Contents"

　　(3) Product Installation Diagram (as described in the instruction manual)

　　1. The circuit breaker is closed, but the machine displays nothing.

　　(1) The machine’s power cord is not connected properly.

　　Diagnosis: Using a multimeter on the AC voltage range, measure between the two input leads of the “over-temperature protector”; no 220 V is present.

　　Remedy: Securely connect the wiring on the circuit breaker. A 220V voltage is now present for the next test.

　　(2) The “over-temperature protector” may enter over-temperature protection mode, or transportation vibrations and damage can also trigger it.

　　Conclusion: Using a multimeter on the AC voltage range, no 220 V was detected between the two output leads of the “two major over-temperature protectors.”

　　Troubleshooting: Manually press the reset button on the “High Over-Temperature Protector” to reset it. After resetting, check for the presence of 220V voltage. If no voltage is present after resetting, replace the “High Over-Temperature Protector.” If 220V voltage is present, proceed to the next test step.

　　(3) Transformer damage.

　　Test conclusion: After energizing for 10 minutes, the transformer core feels no temperature (not hot) to the touch.

　　Action: Replace the transformer. If a temperature (heat) issue is detected, proceed to the next item.

　　(4) The “mini over-temperature protector” has activated for protection or is damaged.

　　Test: Disconnect the plug wire of the “small over-temperature protector,” and directly short-circuit its socket with a screwdriver; the display functions normally.

　　Remedy: Replace the small temperature controller. If there is no display, proceed to the next item.

　　(5) The “Zener diode with aluminum alloy heat sink” is damaged.

　　Diagnosis: Touch the aluminum alloy heat sink of the Zener diode on the “power board.” It feels cold (no temperature).

　　Remedy: Replace the Zener diode. If temperature is involved, proceed to the next item.

　　(6) Poor contact in the display data cable.

　　Conclusion: Pulling the data flex cable produces a display.

　　Remedy: Remove the display data flex cable, reseat it, or replace the cable. If no contact issue is found, proceed to the next step.

　　(7) The display panel is damaged.

　　Conclusion: Replacing the display board restores normal operation. If the issue persists, proceed to the next item.

　　(8) The power board is damaged.

　　Conclusion: Replacing the power board restored normal operation.

　　2. Display fault code A2—leakage (i.e., short circuit)

　　(1) Leakage protection coil.

　　Diagnosis: Remove the plug of the “leakage protection coil”; with power applied, the display still shows A2.

　　Remedy: Replace the damaged leakage current chip and the circuit motherboard. No display; A2 advances to the next item.

　　(2) There is water vapor or moisture on the power board or display board.

　　Test: Power on; display A2.

　　Remedial action: Use a hair dryer to dry any water vapor or moisture on the power board and display board, and at the same time inspect the circuit boards for traces caused by moisture, water vapor, or cockroach excrement, removing them as necessary.

　　(3) The circulation pump is leaking electricity (i.e., short-circuiting).

　　Diagnosis: After powering on, the display shows A2 before the heating mode has been activated.

　　Handling: a. Check the junction box of the circulation pump for water vapor or moisture, and dry it with a hair dryer;

　　b. Replace the circulation pump.

　　(4) Heating element leakage current (i.e., short circuit).

　　Diagnosis: Power on, set to gear 0; A2 is not displayed. Press the Set button, adjust the gear setting, and A2 then appears.

　　Handling: a. Inspect the wiring terminals of the heating element for water vapor and moisture; dry them with a hair dryer. At the same time, check whether the insulation between the connection points and the metal parts of the heating element is damaged, and repair it if necessary.

　　b. Repair the heating element.

　　3. Display fault code A3—Temperature sensor failure

　　(1) The plug is loose, resulting in poor contact.

　　Diagnosis: Pulling on the temperature sensor wire sometimes restores normal readings.

　　Remedy: Locate the poor connection and repair it.

　　(2) The temperature sensor is damaged.

　　Test: Disconnect the temperature sensor connector and measure its resistance with a multimeter. A resistance of 30–150 kΩ indicates a functional sensor; an open circuit or short circuit indicates a faulty sensor.

　　Remedy: Replace with a temperature sensor of the same model.

　　4. Display fault code A4—pressure switch failure

　　(1) Water pressure is too low.

　　Conclusion: The pressure gauge indicates a pressure below 0.08 MPa.

　　Treatment: Increase the water supply pressure to 0.15 MPa.

　　(2) The plug is loose, resulting in poor contact.

　　Diagnosis: Pulling the pressure switch wire sometimes shows normal operation.

　　Remedy: Locate the poor connection and repair it.

　　(3) The pressure switch is damaged.

　　Diagnosis: After replenishing the system pressure, A4 is still displayed.

　　Remedial action: a) Replace the pressure switch; b) For temporary troubleshooting, the pressure switch can be bypassed.

　　5. Displays fault code A1—Overtemperature protection (temperature sensor detects temperature exceeding 90°C)

　　(1) A1 occurs during operation.

　　Cause: Air in the system piping or a blocked pipe, resulting in an over-temperature alarm.

　　Remedial action: Clear any blockages in the system piping and check that all system valves are open.

　　(2) Temperature sensor parameter anomaly.

　　Diagnosis: A1 error occurs immediately upon power-up.

　　Remedy: Replace the temperature sensor.

　　6. How do you bleed an electric wall-mounted boiler?

　　(1) After the machine has been installed, open all valves in the system piping and open the air vent valve.

　　(2) Open the make-up water valve to fill the system to a pressure of 0.2 MPa (see pressure gauge).

　　(3) Power on and set the switch to “0”. The machine’s water pump will start running, but it will not heat.

　　(4) Run the machine in gear 0 for 0.5–1 hour, monitoring the pressure gauge throughout and adding water as needed to maintain a water pressure of 0.15–0.2 MPa. Simultaneously open the air vent valve to release air.

　　(5) After the system has stabilized and no air‑induced noise is present, check the pressure gauge reading and adjust the system pressure to 0.15 MPa. Shift the machine into “Gear 1” and run it for 0.5 hours without any abnormalities.

　　(6) Increase the gear by one level every 15 minutes, gradually setting it to “4”, and run for 0.5 hours without any abnormalities.

　　(7) Set the gear and temperature to the parameters required by the user, then start normal operation.

　　7. What happens if an electric wall-mounted boiler runs dry?

　　(1) The small temperature controller trips, causing a black screen. Power will automatically resume once the heating element cools down and the temperature drops; you will need to restart the device.

　　(2) The main thermostat is disconnected, and the screen goes black.

　　The screen goes black and cannot auto-respond; you need to open the cover and manually reset the main thermostat.

　　(3) After dry‑burning occurs, the cause must be eliminated before normal operation can be resumed. Do not allow repeated dry‑burning, as this may damage the equipment.

　　8. Why does an electric wall-mounted boiler sometimes experience overheating (dry firing)?

　　(1) After an overheating (dry‑burn) condition occurs, the cause must first be eliminated before normal operation can be resumed. Otherwise, repeated overheating (dry‑burn) can easily damage the water circuit and equipment.

　　(2) Improper design of the water circulation system can cause dry‑burning. Automatic thermostatic valves are installed in each room; once the temperature in a room reaches the set point, all such valves close. At that point, water ceases to flow through the piping, leading to dry‑burning. When automatic thermostatic valves must be installed in every room, the system should include bypass lines and bypass valves, or provide two parallel circuits without installing thermostatic valves.

　　(3) If the circulation pump fails to run, dry‑burning can occur. When the pump is not operating, water cannot circulate through the system; if the temperature sensor cannot detect hot water, dry‑burning will result.

　　Remedy: Repair or replace the circulation pump.

　　(4) If the pipeline is blocked and flow is obstructed, dry burning may occur.

　　Remedy: Clear the pipeline.

　　(5) If the valves in the heating system are closed, blocking the flow in the pipes, dry firing can occur.

　　Action: Inspect and open all valves in the system.

　　9. What are the dangers of dry firing an electric wall-mounted boiler?

　　(1) Dry firing an electric wall-mounted boiler will reduce the heater’s service life.

　　(2) Dry firing an electric wall-mounted boiler can easily reduce the service life of the water system.

　　(3) The ultra‑gentle dry‑burn protection device is a safeguard for unexpected situations; it can only prevent the heating element from causing more serious damage due to dry burning.

　　10. Under what conditions should an electric wall-mounted boiler be replenished with water, and at what pressure? Why?

　　(1) When the water pressure in the electric wall-hung boiler system drops to 0.08 MPa, the system must be replenished with water; close the make-up valve when the replenishment pressure reaches 0.15 MPa.

　　(2) When the system pressure drops below 0.05 MPa, the pressure switch trips and the system shuts down.

　　(3) When the system pressure exceeds 0.3 MPa, the pressure relief safety valve will automatically open to release pressure. As the system heats up, the pressure will continue to rise; therefore, the make-up water pressure should not be too high, typically ranging from 0.15 MPa to 0.2 MPa.

　　11. Why doesn’t an 8 kW machine heat up when paired with a 50-square-meter single-story building?

　　(1) When matching heating capacity, the following two key parameters must be considered: the building’s thermal insulation performance (its energy consumption index for heating) and the heated floor area of the room.

　　(2) For an 8 kW unit paired with a 50 m² single-story building, the reason it fails to heat effectively is poor thermal insulation. When selecting the unit’s capacity, insufficient consideration was given to the building’s insulation performance (its heating energy consumption index).

　　(3) When selecting the machine’s power rating, both of the aforementioned parameters should be carefully considered, and the selection should also be matched to the actual heating power requirements of various types of buildings in the local area. Subject to available electrical supply capacity, a higher power rating should be chosen whenever possible.

　　12. Why does the machine keep running without stopping?

　　(1) The machine’s power rating is inappropriate; the power is too low.

　　(2) Based on the actual temperature, reduce the set temperature so that the machine can reach the set temperature and stop to maintain the temperature.

　　(3) Turn off heating in rooms that are not in use.

　　(4) Replace with a higher-power machine.

　　(5) When the machine runs continuously without stopping, it consumes more electricity and fails to achieve the intended heat‑preservation and energy‑saving effect.

　　13. Why does the machine start frequently? Is the heating time too short?

　　(1) If the piping is blocked or the water flow is too low, clean the filter screen and inspect the piping; the water circuit must be a parallel configuration.

　　(2) The circulating pump flow rate is too low. For high‑power wall‑mounted boilers, if the circulating pump is undersized (low flow), it needs to be replaced with a larger one or an additional pump should be installed.

　　(3) Is the circulation pump set to its highest setting (Level III)?

　　14. Regarding the issue of an air switch with leakage protection that cannot be closed?

　　Air circuit breakers and residual current devices (RCDs) are two distinct concepts; an air circuit breaker trips when the current exceeds the load rating.

　　Leakage protection is activated when a voltage imbalance between the live and neutral conductors is detected. If the equipment lacks a grounding conductor, the leakage protection will not operate in the event of a leakage current.

　　15. For a three-phase 380V machine, after installation, the air switch cannot be closed?

　　(1) The wiring of the residual current device (RCD) equipped air switch is incorrect (phase loss); the three live wires and one neutral wire do not all pass through the RCD’s leakage protection coil, resulting in a false leakage indication. All live and neutral conductors must pass through the air switch with built-in RCD protection.

　　(2) The power cable connected to the machine was wired incorrectly, causing a short circuit. The circuit breaker cannot be closed. Inspect and verify the wiring.

　　16. How do you determine whether the machine’s power is sufficient?

　　(1) Shift the machine into 4th gear to initiate the heating process.

　　(2) Use the clamp meter to measure the heating current value I, and simultaneously measure the voltage value V during heating.

　　(3) Calculate the machine’s rated power P:

　　a. Calculate the resistance: R = V/I.

　　b. Calculate the rated power: P = 220²/R

　　(4) Example: For a 220V, 8kW electric wall-mounted boiler, the user reported that it was not heating sufficiently and suspected that the unit’s power was inadequate. After on-site testing by technical personnel, it was found that at the fourth heating level, the actual current (I) was 30A and the actual voltage (V) was 185V.

　　Calculation: R = 185/30 = 6.16. P = 2202/6.16 = 7857 (W). Judgment: The machine’s power is 7857 W. For an 8 kW machine, the acceptable power range is (+5%, -10%): 7200–8400 W. Therefore, the rated power of this unit complies with 8 kW. However, due to the user’s low supply voltage, the actual operating power is only: P = I × V = 30 × 185 = 5550 W.

　　17. Within one minute of powering on, a black screen appears, while the pressure gauge indicates normal water pressure.

　　(1) Pump failure:

　　a. The water pump power cord has come loose;

　　b. The water pump seized up due to prolonged disuse.

　　Solution:

　　a. Use a multimeter to check whether the water pump’s power supply is normal and whether the connections are good. If the controller has no voltage output, it is faulty; replace the controller. If the controller outputs voltage but the pump receives no power, the connector may be loose, making poor contact, or the wire may be broken. If the connector is loose, reconnect it securely; if the contact is poor, ensure a good connection; if the wire is broken, replace it.

　　b. If voltage is being supplied to the pump but it does not turn, the pump may be seized. Loosen the slotted screw on the pump and use a flat‑head screwdriver to turn the pump shaft; rotating the rotor should restore normal operation. If the pump is not seized but a multimeter detects an open circuit or short circuit, the pump is burnt out and must be replaced.

　　(2) Piping failure:

　　a. Air remaining in the pump causes it to run dry.

　　b. The heating system’s distributor is not open, or the filter is clogged.

　　c. Air remains trapped inside the pipeline and has not been fully purged.

　　Solution:

　　a. Unscrew the slotted brass screw on the pump end face, bleed all air from the pump, and restart.

　　b. If the heating system’s distribution valve is closed, open it; if the filter is clogged, remove the filter, flush it thoroughly, reinstall it, perform water filling and air venting, and restart the system.

　　c. If air remains in the pipeline, exhaust it completely and restart.

　　18. The wall-mounted boiler quickly reaches the set temperature, but the radiators remain cold, and the room temperature fails to rise.

　　(1) Cause of failure:

　　a. A large amount of air remains in the heating system and has not been fully vented.

　　b. The heating system is blocked, resulting in slow water circulation.

　　c. Many dispensers are only opened slightly, resulting in a slow water flow.

　　d. The heating system is too large, and the pump power is insufficient.

　　e. Pump impeller damage.

　　f. The pump’s power setting is improperly adjusted.

　　(2) Solution:

　　a. Purge all air from the system.

　　b. Clean the heating system filter.

　　c. Open the distributor appropriately.

　　d. Add an additional pump to increase circulation flow.

　　e. Replace the pump impeller or replace the pump.

　　f. Adjust the water pump to an appropriate setting.

　　19. The heating system is functioning normally, but some radiators are not heating up—what could be the reason?

　　(1) Fault phenomenon: All radiators except one or two are functioning normally; one or two radiators, or one or two groups of radiators, are not heating.

　　(2) Cause of the fault: The radiator distributor for this group is either set too low or contains air.

　　(3) Solution: Increase the opening of the radiator valve that is not heating up, or bleed the air from the radiator.