Why is my water heater making noise?

[herbsells]

We've been at this RV park for 2-1/2 months now and the water heater was always silent until about 2-3 weeks ago when the park had to shut off the park water supply for a short time to make a repair.

After the park water supply was turned back on, and ever since then, when our Atwood 10 gallon hot water heater is actually heating (electric heat element), it makes a clearly audible hissing noise (water boiling I assume?).

So do I have trapped air in the heater? It never did this before and we've owned this coach for over a year now.

I thought it might be trapped air, but I thought that would work it's way out through the faucets in short order, but it's been over two weeks now.

Any ideas out there? Thanks for your help.

[Old-Biscuit]

Electric element.......hissing'
That is due to scaling on the element from minerals in water supply (calcium/magnesium etc)

Can try a power flush......
Turn off water supply
Remove drain plug and then
use a wand on end of hose to flush/rinse thru drain hole (which I find very ineffective due to wand being in drain hole and hole only being 1/2")

OR
With drain plug removed.........
Stand back and turn water supply back on
It will BLOW out thru drain hole.....little messy but it will power flush the tank and blow sediment/scale out. (I turn on ---Blow---turn off let drain a little then turn supply back on repeat couple times....it removes the crud)

IF flush doesn't clean element off then you will need to do a 'vinegar soak' which is detailed in the Atwood manual
4 gallons per 6 gallon tank ( 10 gallon tank would need ~6.5 gallons of vinegar)
Drain water heater tank --put drain plug back in
Remove T&P Relief Valve and pour vinegar in then re-install T&P
Turn on water supply to fill tank
Turn on heat source (electric)
Let water heater go thru 4 heat cycles....heat/cool naturally then heat etc (takes all day/and night to heat/naturally cool (don't use hot water or you will remove the vinegar solution)
Then after 4 heat/cool cycles---drain and FLUSH the crud out

OR you could remove electric element (located on back-side of tank under cover with 120V AC and 12V DC inside cover)
Access can be PITA...but element can be cleaned (soak in CLR or lightly scraped) or replaced with new one

Now if noise is there using propane and not just on electric.
Then that would be an issue with the check valve in hot out (if you have one----not all do---depends on what/how RV Mfg. does install)



Trapped air........
You WANT an air pocket at top of tank.
It naturally forms when filling water heater by design IF you just open a faucet to bleed air in system out (If you open T&P while filling it can cause air pocket to not form)
Air pocket is there to control pressure increases that can occur when heating water. Hot water swells and w/o air pocket to absorb this swelling pressure will increase (can't compress water) enough to cause T&P to 'weep'
So air pocket s a good thing

[herbsells]

WOW! Thanks so much for all the detailed info .... I hope I don't have to remove the element because like you say it would be a PITA where the heater is located I can only reach one arm in there at a time, so hopefully the flush or vinegar wash will work.
Thanks again ...