To answer the question why is my cold water valve (or ECV) on my Sanden leaking a lot what is causing this? A few elements to consider.
To protect your Sanden unit from excessive pressure there are three valves:
Valve 1. The pressure reduction valve (PRV) which is located on the water inlet to your home and is set to 500kPa. This valve is designed to keep the pressure out of any tap in your house below 500 kPa.
Valve 2. The expansion control valve (ECV) which is located on the cold water inlet to your Sanden and is set to 600 kPa. This valve is designed to relieve cold water instead of hot water during the heating cycle (which increases pressure in the tank) which saves you money and protects the final valve, the PTR.
Valve 3. The Pressure and temperature relief valve (PTR) which is located on the hot water outlet to the Sanden and is set to 700 kPa. This valve is designed to release hot water from your tank if the pressure gets too high or the water heating cut-off fails to work.
One of the main reasons ECV valves leak water excessively (apart from wear and tear or malfunction) is excessive water pressure in the mains supply which is not properly being reduced by a PRV as it enters your house to at or below 500 kPa; in many areas the mains water pressure is 850 kPa + this is to ensure fire fighters have enough pressure to use their fire hoses properly in the event of a fire.
Note: the Australian standard covering water pressure in the home (AS 3500.1:2018) mandates that water pressure in your home must be kept below 500 kPa as water pressure above 500 kPa has the potential to damage valves, tap fittings, flexible hose fitting etc as the components are only rated to withstand pressures at or below 500 kPa.
So if you notice that the expansion control valve (valve 2 discussed earlier) on your Sanden is leaking excessively chances are you have excessive water pressure at your house and your PRV (valve 1) is either not present or not working.
Either way you should get a plumber to check the water pressure in your house and make sure you have a functional PRV. You can also buy a cheap pressure meter from a hardware shop if you want to check your household water pressure yourself: Note your mains pressure is not constant it will change based on a number of factors including local water use, time of day, time of year or changes in your local area such as new housing being built etc.
