Last week I replaced a leaking relief valve in my water heater. the water heater is about six years old, and the valve I removed was heavily encrusted with deposits. One of the interesting things was that it was not a uniform coating; instead, it seemed like solids were precipitating out of solution and then settling via gravity onto the upper surfaces of the valve assembly. There was a ridge of crust on the top surface of the temperature probe, and relatively little on the bottom surface.
I recall from basic chemistry that solids tend to exhibit increased solubility when the liquid into which they are dissolving is warmed up. OK, so we’re bringing cold water into the water heater with a certain amount of dissolved solids, and then we’re heating the water up. The water’s hot, but it’s not evaporating; it’s under pressure in an enclosed tank. So we’ve got a solution of fixed concentration, and we’ve heated it up - so why are these dissolved solids coming out of solution in the water heater???
Calcium carbonate is a common substance dissolved in tap water. It is also a unique compound with the characteristic that it precipitates when the solution is HEATED.
The common name for this is “lime scale.” It’s also the crud in the bottom of teapots and coffeemakers, and if you have a LOT of lime in your local water, you’ll find it caked around faucets and crusting in washing machines and dishwashers.
Vinegar is the best solvent for lime scale. For coffeemakers, tea kettles, and major appliances, a regular descaling with vinegar is the best maintenance.
For hot water heaters, the tank needs to be drained regularly to remove the sediment at the bottom. It can actually build up on the heating element and make the appliance less efficient as time goes on. A really OLD water heater will often rumble when it heats up, which is the water bubbling through the crud. NOT very safe at all.
~VOW
I had a similar problem but I don’t think it was exactly the same.
I had replaced my electric hw heater about 5 years ago. One day, it started tripping the circuit breaker. After a false start, the plumber figured out the problem. There was thick layer of what looked like a translucent crystal covering the entire interior surface of the tank. I assume this included the electrodes. Apparently when the the circuit was switched on, it drew too much current for too long and that was enough to trip the breaker. I don’t exactly understand the connection although the explanation seemed to make sense at the time (I hate when that happens).
In my case though, since I’m disabled and live alone (lately anyway), I don’t use a lot of hot water. Even for washing clothes, you don’t do a lot of loads when it’s mainly jeans and t-shirts. So I wonder how much that plays into it. IOW, maybe i wouldn’t be getting that layer of calcite or whatever it is if I used 2 or 3 times more hot water than I do.