Replacing the Thermostat in Your Hot Water System

hot water thermostat

Over time our hot water systems age and deteriorate, just like any appliance in our homes, but it’s not until they stop working that we think to check them. If your hot water tank isn’t producing hot water anymore, it’s likely due to one of two issues:

  1. The thermostat
  2. The heating element

While you could call out a service technician, DIY replacement of either part is definitely achievable, so in this article, we’re going to talk you through how to replace your hot water thermostat.

What are the components of a hot water system?

In Australia, water heating is the second largest household energy expense, consuming anywhere from 15% - 27% of your household energy. Electric hot water storage systems are found in around 50% of Australian households, mainly because they’re the cheapest type to buy and install. They’re made up of the following components:

  • Storage tank – stores the water
  • Heater element – creates the heat needed to heat the water
  • Thermostat – controls the water temperature within the storage tank
  • Temperature pressure relief valve – protects the tank from excess pressures and temperatures
  • Anode rod – helps mitigate corrosion in the tank
  • Drain valve – drains the tank so repairs can be carried out, or the tank moved

What are the signs that it’s time to replace the thermostat?

Most modern residential hot water systems have two heating elements and two thermostats, and they control heating and maintaining the water temperature. If you have no hot water, inconsistent hot water, or the tank takes too long to reheat, it is likely to be due to these needing replacement.

If your upper thermostat is faulty, the water tank will stop heating water entirely. If the lower thermostat is faulty, the hot water will only be lukewarm or it will quickly run out.

How do I replace my hot water thermostat?

Tools needed:

  • A flathead screwdriver and a Phillips screwdriver
  • An analogue or digital multimeter
  • The replacement thermostat part

Step by step replacement:

  1. Turn off the power from your circuit board/mains – look for the water heater breaker, and turn it off
  2. Remove the exterior access covers using your flathead screwdriver
  3. Pull out the insulation and you’ll see the top thermostat and heating element, which sits under a clear plastic cover
  4. The thermostat has an in-built circuit breaker with a button which acts as a reset; push it to make sure it hasn’t just tripped. If it has just tripped, you’ll hear a snap, so turn the power on and the water will start heating. If that’s the case – you can finish here!
  5. If it hasn’t just tripped, it needs replacing, so remove the plastic cover from the thermostat and use your multimeter to test there’s no power going to it – check the top two screws and as long as no voltage is detected, there is no power

Do not proceed until you are certain there is no power to the tank!

  1. Disconnect the wiring next; with your Phillips screwdriver, loosen and remove the terminal screws (tip: take a photo with your phone of the wiring connections, because you’ll need to reconnect them after)
  2. Check your thermostat terminals with the multimeter set to the lowest ohms of resistance – use the black probe to test the left side terminal by the reset button, and the red probe to test the second left side terminal. The reading should be close to 0 if the thermostat is NOT faulty. Repeat for the right-hand side
  3. If either thermostat is faulty, then you’ll need to replace it. To do this, remove the faulty thermostat using your flathead screwdriver and pressing out on the clips to lift it out of the bracket VERY carefully (if you damage this bracket, it can’t be replaced, which means you’ll need to replace the entire water tank)
  4. Fit the new thermostat in, also VERY carefully, and rewire tightly
  5. Set the new thermostat to temperature (65 degrees Celsius is recommended) and replace the cover
  6. Turn the power back on, and allow up to an hour for the water tank to heat

Need a replacement thermostat for your hot water system?

Your hot water system is a critical appliance that you take for granted until it stops working. Home repairs and replacements are achievable with a few common tools and with replacement parts from Wayne’s Wholesale Spares. We stock hot water thermostats, and a range of other parts to service and repair your hot water system, so that you can get the hot water back on quickly and easily.

For all your spare parts needs and friendly, helpful advice, get in contact – we’re here to help.