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Frequently asked questions about electric water heaters

General FAQ

Viessmann is one of the world’s leading providers of sustainable climate (heating, cooling, water, and air quality) and renewable energy solutions with over 100 years of German heritage and industry-leading expertise. Viessmann SEA focuses on the product categories – water heaters and water purification products.

  • High-Quality German Engineering: Viessmann is a German company with a strong reputation for precision engineering and high-quality manufacturing. German engineering is often associated with reliability and innovation.
  • Reliability: Viessmann products are known for their long-term reliability and durability. This reputation for longevity can be reassuring for customers looking for products that will last.
  • Service and Support: Viessmann provides excellent customer support and service. Their products are often backed by warranties, and they offer maintenance and service plans to ensure ongoing performance.

An instant water heater provides instantaneous heating to the water flowing through the device. It does not have a storage tank to contain any heated water.   Instant water heater is usually catered to a single point of use, mainly for bathroom shower.  

On the other hand, a storage water heater comes with a water tank where the cold water is stored and heated. The heated water is then drawn out from the storage water heater and supply to various hot water outlets in the household, such as shower mixer taps, kitchen sink faucets, bath mixer.

When the water pressure is too low, the water discharge becomes weak. Unfortunately, there is no way you can adjust the water pressure from the Storage water heater because the water pressure is all dependent on the water supply into your household and the water heater does not regulate water pressure. For Instant water heaters, Viessmann provides products equipped with a DC water Pump to boost the water flow to customer expectations in case of low water pressure from the house.

Besides water pressure, you also need to check on the water flow rate. Water flow rate defines the amount of water flowing through the supply pipe per time, while water pressure defines the force that pushes this amount of water through the supply pipe. If the water flow is poor, the water discharge at your shower for instance can still be weak no matter how much pressure is introduced.  

Poor water flow commonly arises from pipe clogging, or having smaller piping size at certain sections of the supply pipe. You may consult a licensed plumber for further advice to address such problems.

Taking a shower head as an example,

  1. Turn the shower on full.
  2. Take a measuring jar and place it at the showerhead to collect discharged water.
  3. Time for 10 sec and move the measuring jar away from the showerhead to stop the collection.
  4. Obtain the volume of the water collected in the measuring jar and multiply by 6. This will give you an estimated flow rate per minute.

There are few possible causes relating to electrical wiring/ electrical supply problems.

  • Wrong wiring connection, or worn/damaged cables that has fused or come into contact with each other, leading to a short circuit
  • Failure to wire to a dedicated power point/socket with sufficient electrical rating to support the water heater use.
  • Sharing of the power point/socket with other electrical appliance(s) resulting in electrical overload. The power point for water heater should never be shared.
  • Faulty heater switch / power point.

Please consult an electrician to check and rectify any electrical problem. If power trip persists even after electrical inspection, kindly contact Viessmann Service Support to check and service on your water heater unit.

FAQ on instant water heaters

Make sure that the water inlet and outlet are connected correctly. One of the safety features in Viessmann Instant water heaters is that heating will not be activated when the water inflow and outflow is detected to be incorrect. You may refer to the label on the underside of the heater unit to identify the heater inlet and outlet.

Make sure that the water flow rate is at least 2L/min and pressure is at least 0.1bar, otherwise heating will not be activated.

If the water heater is still not working, kindly contact Viessmann Service Support to check and service on the water heater unit.

Sometimes, your shower water may not be hot enough due to these reasons:

  • Water flow rate is too high: For instant water heater, the heating element generates heat to the water flowing through it. There is a maximum amount of heat that can be produced when the heater unit reaches its maximum operating power. If the water flow rate is too high, the same amount of heat produced has to be distributed among a larger volume of water flowing through, and so the temperature of the water outflow will be generally lower. In such situation, turn on the shower tap partially instead, or install a flow restrictor to reduce the water supplying to the water heater.
  • Water pressure is too high:  When the water is flowing too fast due to high pressure, the fast-flowing water will not be able to heat up efficiently and so the temperature of the water outflow will be lower. Ensure that the water pressure is within the recommended operating range of 0.1 – 6 bar.
  • Water supply is too cold:  If the temperature of water supply is significantly lower than usual, even the maximum amount of heat generated may still be insufficient to raise the temperature of the cold water instantly to the desired temperature.

When water discharge becomes weak at showerhead, there could be clogging of sediment at the filters of the stop valve. Take out the Filters and flush them with water to remove any trapped sediments.

Stain or substance at showerhead/clogging of showerhead nozzles are typically formed from the buildup of particulate minerals e.g. iron, calcium carbonate found in water supply. Remove the showerhead and rinse the deposit away with water.

FAQ on storage water heaters

Before turning on the electrical supply, turn on the water supply to ensure that your storage water heater is completely filled up with water. This is an important step to avoid dryburn and damage to the thermal components such as thermostat and heating element.

Make sure that the water inlet and outlet have been connected correctly, otherwise colder water in the storage tank will be dispensed first. The red and blue rings on the underside of the Viessmann storage water heater indicate the hot water outlet and cold water inlet respectively.

This image shows the bottom of the Vitowell comfort Classic (cube).

If the above conditions have been fulfilled and your water heater is still not working, please contact Viessmann Service Support to check and service on the water heater unit.

  • The water in the storage water heater may not have fully heated up yet. Hence, give some time for the water to get heated up before use. The light indicators on Viessmann storage water heaters are a good way to recognize whether the heating process is completed.
  • Water flow rate at the water fixture (e.g. shower) which draws hot water from the storage water heater is too high. This means the hot water stored at the heater is consumed faster than the rate at which the cold water refilled into the tank can be fully heated up. In such a situation, turn on the water fixture tap partially instead, or install a flow restrictor to reduce the water flow.

Use the light indicators on Viessmann storage water heaters to easily recognise whether the heating process is completed.

Heating progress

Vitowell comfort Premium/Deluxe
Vitowell comfort Classic

Pressure relief valve is necessary to be installed at the cold water inlet of the storage water heater to prevent tank overpressure, leakage, or explosion in the worst case. You can find a pressure relief valve included in the accessory pack of every Viessmann storage water heater unit supplied.

Whenever the water pressure at the water heater is too high, the pressure relief valve will release excess pressure through releasing/dripping of water. This releasing/dripping of water will stop when the water pressure is reduced and stabilized.

To check if releasing/dripping of water arises from the normal operation of the pressure relief valve, you can simply turn on water at the shower for 20-30 sec, and observe if the drip at the pressure relief valve stops.

If water dripping occurs permanently, kindly contact Viessmann Service Support to check and rectify on the possible faulty pressure relief valve.

To ensure the best performance from this appliance, it is recommended to replace the magnesium anode, flush out any deposit of salts in the heater tank and descale the heating element once every two years. The maintenance cycle may vary depending on the water quality. It is necessary to   engage a plumber or service technician to perform the maintenance operation.

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