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Frequently asked questions about electric water heaters

General FAQ

  Instant water heatersStorage water heaters    
HeatingInstantaneous heating to the water flowing through the deviceCold water is stored and heated in a tank over time    
UsageSingle point of use (mainly for bathroom shower)Multiple points of use (shower mixer, kitchen sink faucets, bathroom taps)    

Which water heater should I get?

Getting a water heater, but not sure which one is right? Our Bathroom Guide provides information on the various types of water heaters and tips and advice when it comes to choosing the right one for your home.

When the water pressure is too low, the water discharge become weak. Unfortunately, there is no way that you can adjust the water pressure from the water heater because the water pressure depends entirely on the water supply into your household and the water heater does not regulate water pressure.

In fact, when the water pressure to your household is low, you may notice that the water discharge from other water fixtures in your household will also be weak since they share the same water pipe distribution. You may wish to consider installing a pressure regulator/booster at your supply pipe. Please consult a Licensed Plumber for further advice on water pressure issues.

If the water pressure is within the recommended operating range, a poor water flow rate could be the reason why the water discharge from your water heater is still weak.

Water flow rate is defined as the amount of water flowing through the supply pipe per time, while water pressure is defined as the force that pushes this amount of water through the supply pipe. If the flow rate from your water fixture is poor, the water discharge can still be weak no matter how much pressure is introduced.

A simple way to check for poor water flow is by first turning on water at one water fixture e.g. hand shower, and then observe for any drop in the water discharge/water throw when water is turned on concurrently at another water fixture e.g. basin tap, or flushing at the water closet.

A common cause for poor water flow is due to pipe clogging, or smaller piping size at sections of the supply pipe. Please consult a Licensed Plumber for further advice on water flow issues.

Taking a shower head as an example,

  1. Turn the shower on full.
  2. Use a measuring jar to collect the water that is discharged from the shower head.
  3. Do this for 10 seconds and move the measuring jar away from the showerhead to stop the collection.

Obtain the volume of the water collected in the measuring jar and multiply by 6 to obtain an estimated flow rate per minute.

A power trip at home  caused by the turning on of the electric water heater is usually related to electrical wiring/ electrical supply problems that fall under these common causes:

  • 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 water heater power point/ front flex outlet. A 3-pin socket outlet should not be used because its power rating is insufficient to support water heater.
  • 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 a Licensed Electrician to check and rectify any electrical problem. If the power trip persists even after an electrical inspection, kindly contact Viessmann Service Support to check and service your water heater unit.

Based on PUB's Stipulation of Standards & Requirements, water fittings for use in potable water service installations, especially for storage water heaters, must be carried out and certified by Licensed Plumbers. Viessmann reserves the right to void the warranty if product failure is found to be associated with improper installation performed by unlicensed workers/handyman.

FAQ on instant water heaters

Check if the water inlet and outlet of your device have been connected correctly, as heating may have been deactivated as a safety feature in Viessmann instant water heaters in the following conditions:

  1. when the water inflow and outflow is detected to be incorrect. (Refer to the label on the underside of the heater unit to identify the heater inlet and outlet.)
  2. when the water flow rate is below 2L/min and/or water pressure is below 0.1bar

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.

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 a situation, turn on the shower tap partially instead, or install a flow restrictor (of around 5-6L/min flow rate ideally) 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 can be 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.

Over time, clogging of sediments at the filters of the stop valve and clogging of showerhead nozzles from the build-up of particulate minerals (e.g. iron, calcium carbonate in household water) can weaken the discharge of water at the shower head. These regular maintenance actions can be taken to maintain the water discharge:

  • Remove the filters and flush them with water to remove any trapped sediments
  • 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.

There are 2 common reasons why the water from your storage heater is not hot enough:

  • Water not fully heated up yet: give some time for the water to be heated up before use.
  • Water flow rate at water fixture is too high:  hot water stored at the heater is being 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

Under Singapore regulation SS636:2018, 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 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 arise 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 best to engage a Licensed Plumber or service technician to perform the maintenance operation.

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