Brainiac needed for auditory mystery

[Nathan Pate]

Sporadically, our SDHW system produces a LOUD "boink" or bang, which sounds like a single HARD whallop on a kettle drum. This cannot be good; I'm guessing it's the storage tank bottom (top?) flexing in some way. We are on well water so there is an "expansion tank"/pressure tank in the garage, which feeds water to SDHW system in mechanical room. This nerve-wracking boink never happens when the system is running, but only when it is in cool-down mode, I'm pretty sure. Does anyone know what causes these isolated, loud whangs?

User manual for storage tanks says that a "thermal expansion tank" must be installed on cold water input. However, my contractor (in whom i've lost all confidence, but that's another story) who installed this did not put one in. Shouldn't the (garage) expansion tank already in place perform this function?

In short, do I have a problem, and if so, what's the solution?

[Joe Blake]

I know VERY little about solar HWS (although I have one on my roof :embarrassedt:) but from your description, particularly the bit about only seeming to happen in "cool down mode" makes me think of pressure dropping inside a sealed vessel as the contents cool, then the metal wall suddenly giving under the pressure. Alternatively, perhaps the metal wall is slowly bending in, then somewhere a pressure valve opens and equalises the pressure and the metal "pops" out again.

Either way doesn't sound good, because repeated flexing can weaken metal and perhaps will eventually cause a rupture somewhere.

Here endeth my feeble attempt at guessing.:bigsmile:

Joe

[Dave Turpin]

I would have to see the system to diagnose it. Metal pipes expand when heated. There are all sorts of noises a system will make if the pipes were not routed to account for expansion.