Hi I have just brought a house with and 30 year old electric hot water cylinder.

I have it set at 65deg and 70 comes out of the hot tape. After 5 mins its down to 40deg and after 10 mins 30deg. The pressure is good. Flow rate is approx 20 liters per minute from hot and I bit higher from the cold. I have replaced the element and the thermostat is working fine. Nothing states capacity of cylinder.

I have drained the cylinder and flashed out the best i can. This was after I ran the hot tap for a good 10 minutes, it still had plenty of water as it run at around 30deg out the drain for a least 10 minutes.

After a 5 min shower you have to keep turning the tap to hold a showering temp. After 5 mins the water is barely warm enough and the pressure is almost a lot lower as you twist the tap towards hot.

I have pictures http://sdrv.ms/16rwbyn

I need to understand hows this works. Why is this behaving this way? Does this sound right? Is my flow rate to high? Am i using all the capacity of the cylinder? Can this be fixed? Or is it a new one job?

Thanks a lot in advance.

 

Linkback: https://www.plumbers.nz/q-and-a-hot-water-cylinders/44/hot-water-cylinder-hot-and-gets-cold-quick/1473/

Hi is  this what they call an elephant cylinder?
 I gather that the low pressure water in the cylinder heats the mains pressure water in the coil. basically a heat exchanger.
I have seen systems like this but without the header tank on top, fed by a pressure reducing valve.

Yip this is an Elephant, boots what your saying above is correct. There are minor things you can do though to improve your hot water time. You mention that you get 70deg at the tap, you should really have a tempering valve (by law) in between and restrictors on your shower/tapware, this will reduce your flow and demand on the coil during usage allowing it to heat up much quicker. Hunson's don't operate that well on todays mains pressure and preform better on medium pressure. I would also check the thermostat to determine how accurate it is, at what temperature does it activate the element? There are several posts on this forum about elephants, use the search you might find more helpful info. Alternatively like you say a new mains pressure tank will do the trick

All the best! Look forward to hearing about your renovation