I made this GIF from an experiment done by Myth Busters to show the extent of damage a hot water cylinder can do when there is no pressure relief.
The image above reinforces the importance of using individuals that understand the physics of hot water and the effects an installation can have on its surroundings.
So at what point will a cylinder explode?
In principal it’s simple to understand. Heating a substance causes molecules to speed up and spread slightly further apart, occupying a larger volume that results in a decrease in density. So “larger volume” means “more space” which is limited to the size of the hot water cylinder.
If hot water is not used and your thermostat fails, your immersion element will continue heating your water (to boiling point) until such time one of the pressure relief valves activates and relieves the pressure. Every installation should include two relief valves, one on the cold water side and one on the hot water side.
This regulation was put in place around 1997 meaning that any cylinders installed prior to that may only have one source of pressure relief. Hence the low pressure vent copper pipe going through the roof.
This is where it gets tricky. Many installers dont bother replacing older valves when replacing an old hot water cylinder with a new one. Others have managed to install a tempering valve on a low pressure system right into the overflow pipe, blocking the only means of pressure relief. The hot water system then becomes a time bomb which may result in something pictured above.
Sometimes its not the plumbers’ fault but rather the homeowner who sees a pipe dripping on the outside of a house and thinks.. “Oh, this should not be leaking” and decides to “blank” it off by any means available, creating the perfect conditions for a catastrophe. My recommendation on this is, see a dripping pipe? Please call the plumber.
If you are unsure about what valves you need or already have, send us an email or give us a call for help.
Very often we get clients calling us saying there is a pipe that is constantly dripping outside their house and they want it fixed so that it stops. The first thing that we do Is try to educate the clients on what the role of this valve is along with the rest of the valves on the hot water cylinder. So what does a Cold Water Expansion valve do??
When your cylinder is filled with cooler water at high pressure after you, let’s say have used it for a shower or filling the sink with hot water, the element comes on to heat the water back up to it maximum temperature. The water being heated up causes the water molecules expand and increases the already high pressure in your hot water cylinder to even higher. The Cold Water Expansion has 2 roles in this situation,
- it’s a safety mechanism that releases excess water pressure from your hot water cylinder as it heats up to avoid over pressurizing,
- it’s a energy saving device, because it is installed where the cold water comes into your cylinder, it drips out cold water instead of other valves at the top of your cylinder wasting and dripping hot water.
So this valve is made to drip while the cylinder is heating, however if yours is dripping all day and all night constantly this may indicate it is time get us in to replace the valve or investigate other issues that may be forcing the valve to drip.
How do I know my cold water expansion valve is working?
Check that the valves on-top of your cylinder are not discharging any water because if they are then the cold water expansion valve isn’t doing its job, also when you do manually turn your cold water expansion valve on, look for discoloration of the water as this indicates the valve is rusted internally or the rubber seal has perished and is no longer effective. If you are still concerned, getting a hot water cylinder service by us includes checking this valve and others thoroughly.