Water tank questions

rsynnott

I've got one of those big green foam-covered hot and cold combo water tanks (picture attached). I've noticed that for a long time after the water's used there's a hissing and dripping noise, like water entering it. It does eventually stop. The hissing is sometimes intermittent. It's been like this since I moved in a couple of years ago.

I never thought much of it, because I used to rent an apartment with a similar tank and it did something similar, but was just wondering if it was normal or if something's going on. I'd expect it to fill up pretty quickly once some water was used. It seems to work fine, otherwise.

I can find no evidence of anything fed by it dripping or leaking, and it's reliably stopped in the morning, and when I get home from work. It just seems like it's filling very slowly and noisily.

Also, more out of curiosity than anything else, anyone know how do these tanks work? What happens to the excess water when the hot tank is heated and expands?

K.Flyer

Usually the continuous sound of dripping and hissing would be an indication of a worn filling valve. The foam covered tube running up the side of the upper section is the expansion pipe from the hot water section underneath.
My recommendation for filling valves on these tanks is the FluidMaster Pro75 B. When set up correctly you will hardly hear water re-filling the tank from a 6 litre toilet flush, and when the tank is full it shuts off completely with no prolonged dripping or hissing sounds.

rsynnott

Brilliant, thanks, makes sense. Is the filling valve attached on the top of these? It's hard to see what's going on there, because it's kind of partially boxed in (pic attached); it's behind a lowish door and there's a wooden panel on top, covering the top of the tank.

What's eventual failure of one of these valves look like? Will it just slowly stop filling entirely, or something messier?

Also, what sort of lifespan do these tanks have? This one's 10 years old; should I be expecting to have to get a few more years out of it?

K.Flyer

The filling valve is at the top of the tank, 1/2" pipe, with the over flow pipe a couple of inches below that, usually 3/4" pipe.
If the valve fails to close water should leave by the overflow as long as its installed correctly and not blocked.
If the tank runs empty its an indication of the valve being blocked.
Life span on these type of tanks vary, I've seen tanks less than 10 years having to be replaced, while much older are fine. They tend to leak where the two sections join and are not repairable.
Keep an occasional eye on the ground around the base of the tank and pump for damp, its usually a sign of a leak.

rsynnott

Great, thanks. There's no obvious damp, anyway. There's a bit of corrosion around the valve at the bottom of the cold water part (unused valve; I think it's probably there for draining it or something), but it's old and dry, doesn't seem to be a current leak.

rsynnott

So, just having another look at the tank, and trying to make sense of what I'm seeing. Access to the top is limited. Two photos attached, the first is, I'm pretty sure, the water inlet, which looks like it's going straight in. This is at the front of the tank at the top. The second I'm guessing must be the overflow. This is a slightly thicker plastic-y pipe right at the back of the tank, against the wall.

Where would the fill valve be in all this?

K.Flyer

Plastic pipe is the overflow and the thinner copper pipe is the water supply to the tank and the filling valve (ball-cock) is attached to the copper pipe (inside the tank).

rsynnott

Ah, cool, thanks. Accessed via the lid on the top? I think it’s a lid, anyway, it’s hard to get access to the top.

K.Flyer

Yes, the lid just pops off. Some of them can be an absolute nightmare to change the valve, some are impossible to do without making an opening or doing it blind.