Never enough hot water

Cause

Water heater undersized for hot water demand

Repair

  • a hot water storage cylinder must be large enough to provide for a household’s peak hot water demand, but energy will be wasted if the cylinder is too large. The appropriate size depends primarily on the number of people in the household. Typical hot water usage is around 40–60 litres per person per day

  • when determining the size, the water heater should be able to maintain 75% of its capacity as hot water. For example, where there is a demand of 135 litres, a 180 litre cylinder should be installed

  • as a general guide, an average 2–3 person household should find a 180 litre cylinder sufficient; a 4–person household, 250 or 300 litre

  • if installing a new hot water system is not possible, hot water usage can be reduced by fitting low-flow showerheads to showers and aerators (flow reducers) to taps in hand basins

  • if installing a new hot water system is a possibility, you can find useful information about water heating systems on the government’s Gen Less website

Cause

Crossed hot and cold water connections due to faulty plumbing installation

Repair

  • to check for a crossed connection:
    • close the water shut-off valve
    • turn on a hot water faucet
    • if there is water flow, there is a crossed connection in the system

Cause

Faulty heating element 

Repair

  • homeowners are permitted to remove and replace water heater elements so long as it does not involve work on a switchboard. (The details are in the Electricity Act 1992 sections 79 and 80, and NZECP 51:2004 New Zealand Electrical Code of Practice for Homeowner/Occupier’s Electrical Wiring Work in Domestic Installations.) Landlords/ business owners cannot carry out electrical work in their rental properties or workplaces unless they hold the relevant licence

  • homeowners should only make this repair themselves if they have the skills, experience and tools to be able to safely and competently complete the job. You are required by law to carry out the work “in a workmanlike manner” and in compliance with all the relevant laws and codes

  • most homeowners should call a licensed plumber

  • turn the power off and water heater off. Drain the cylinder then remove the heating element and replace. Ensure you replace the old element with a new one of equal wattage. If the original element was 2kW, then the replacement element should also be 2kW and no higher

  • with very old cylinders, be aware that changes in pressure in the cylinder that come about from switching off, draining, refilling and switching on a tank again may potentially lead to stresses and leaks, for example in a welded seam. Carefully consider repair vs replacement. Replacement with a new cylinder must be carried out by a licensed plumber

  • you can find useful information about water heating systems on the government’s Gen Less website

Cause

Thermostat setting too low

Repair

  • reset the thermostat. Stored hot water should reach no less than 60°C at least once per day to avoid the growth of Legionella bacteria. However, the delivery temperature of hot water to sanitary fixtures used for personal hygiene such as baths, showers and hand basins must be no more than 55°C

  • if the thermostat is faulty it should be replaced

  • homeowners are permitted to remove and replace a water heater thermostat so long as it does not involve work on a switchboard. (The details are in the Electricity Act 1992 sections 79 and 80, and NZECP 51:2004 New Zealand Electrical Code of Practice for Homeowner/Occupier’s Electrical Wiring Work in Domestic Installations.) Landlords/ business owners cannot carry out electrical work in their rental properties or workplaces unless they hold the relevant licence

  • homeowners should only make this repair themselves if they have the skills, experience and tools to be able to safely and competently complete the job. You are required by law to carry out the work “in a workmanlike manner” and in compliance with all the relevant laws and codes

  • most homeowners should call a licensed plumber