Guide to Replacing your Hot Water Cylinder

A DIY hot water cylinder job isn’t very common, but with the right knowledge it can be done. If your current system is damaged, leaking or is simply very old, replacing it can potentially be a simple process. Of course, it is highly recommended to get this task done by a professional to prevent any accidents or injuries. Don’t hesitate to stop and seek advice if something goes wrong during your project.

Know what you’re dealing with

Start by assessing what type of hot water cylinders you’re working with. You want to ensure that the replacement model will fit in the space you have. If you intend to put the new system in a different location, you should consult with a professional to make sure it will work. It is recommended to purchase a pre-insulated model, as this will last longer.

If you’re planning on installing a thermal or unvented system, consult a professional – these cannot be done on a DIY basis.

Tools you will need

Make sure you own (or have hired) the right tools for the job! Here’s a list of what you will need to install a hot water cylinder:

  • Immersion spanner
  • Adjustable wrench
  • Plumbers tape
  • Electrical tape
  • Screwdriver
  • Tube cutter
  • Safety goggles
  • Voltage tester
  • Pipe wrench
  • Soldering torch
  • Wire cutter
  • Fittings
  • Solder
  • Pressure relief valve
  • Discharge pipe
  • Pipe thread compound
  • Venting pipe & connectors

Remove the old system

Begin by isolating the old hot water cylinder and draining it completely. You will need to turn off the supply of cold H2O and switch off mains electricity on your property. Disconnect your immersion heater from this mains electrical supply and drain it using the drain cock at the base. It is recommended to take note of the position of each plumbing fixture while you dismantle them, so that connecting your new system will be easier. You can add a description using masking tape and a pen.

Continue disconnecting all pipes and fastening them away. You may need to use some penetrating oil if any of the joints are stiff. Then take the hot water cylinder out and move it somewhere safe. You can then inspect the pipework and cupboard for signs of wear and clean it out a bit.


Installing your new system

It is now time to prepare your area for the new model! It is a good idea to put a gate valve on your outlet pipe if you do not already have one – this will make future dismantling and installations easier. Then check that your base is large and firm enough for your new tank. If you need a better one you can make one using plywood.

Next, put your new hot water cylinder in the correct position, ensuring it is firm on the base. You can then start to connect all the fittings and pipes. You might need to modify some of them so that they fit properly. Use your tape to ensure the joints are tight. You can fit the draincock to your tank feedpipe (from your cold H2O tank) if you don’t already have one.

You will then need to reinstall your immersion heater and make sure you wrap the tape around any threads for a tight fit. Then reconnect your immersion heater to the overall electrical system. You can then fill up the model and check for any leaks. If you are happy with your hot water cylinder job, start the boiler and heat up your H2O! Again, check for leaks as it heats up. If all is well, then congratulations – you’re done!


December 2, 2019 Annette Welch