4 years ago my mother’s cylinder, element and stat were changed. Last week she used it for the first time and after 5 or so minutes heating from stone cold (about 15C) it stopped working. I found the stat open circuit so changed it, but the same thing happened with the new one. I noticed that the overheat trip had tripped on the original one and the new one may have done the same but reset itself.
I have now changed it for an old stat I had without an overheat trip and all is OK except that the water gets far hotter than the stat dial says.
My speculation as to what is happening is:-
This is a flat topped cylinder with a top mounted element, thus the element is completely vertical. When it starts heating, the hot water rises vertically and heats up the top of the element and the metal around the heater head. This may get to more than the trip temperature even though the average temperature across the stat rod is still only 20C or so. Thus it trips prematurely. Most elements are mounted angled or horizontal so the rising hot water is not going to heat the element head so much.
Is my speculation correct and what can be done to cure it? Is there available any alternative sort of element or stat for vertical installations like this? What temperature point is the overheat stat measuring? – an average temperature over the rod or just the temperature at the stat head?
Other possibilities are that the element is seriously bent so is touching the stat tube near the head or there is a flaw in the element so it's producing a lot of heat near the head. But that does not explain the excess temperature on the current old stat. Or the element is faulty and taking much more current than it should, overheating the stat through resistance heating. But the 13amp fuse does not blow.
The old stat I used is about 250mm long and the tube is about 400mm long. Is there any safety issue with using a shorter stat than the tube? Operationally it's only the top part of tank she wants heated so a short stat may be advantageous.
I have now changed it for an old stat I had without an overheat trip and all is OK except that the water gets far hotter than the stat dial says.
My speculation as to what is happening is:-
This is a flat topped cylinder with a top mounted element, thus the element is completely vertical. When it starts heating, the hot water rises vertically and heats up the top of the element and the metal around the heater head. This may get to more than the trip temperature even though the average temperature across the stat rod is still only 20C or so. Thus it trips prematurely. Most elements are mounted angled or horizontal so the rising hot water is not going to heat the element head so much.
Is my speculation correct and what can be done to cure it? Is there available any alternative sort of element or stat for vertical installations like this? What temperature point is the overheat stat measuring? – an average temperature over the rod or just the temperature at the stat head?
Other possibilities are that the element is seriously bent so is touching the stat tube near the head or there is a flaw in the element so it's producing a lot of heat near the head. But that does not explain the excess temperature on the current old stat. Or the element is faulty and taking much more current than it should, overheating the stat through resistance heating. But the 13amp fuse does not blow.
The old stat I used is about 250mm long and the tube is about 400mm long. Is there any safety issue with using a shorter stat than the tube? Operationally it's only the top part of tank she wants heated so a short stat may be advantageous.
