rumbling in the gas hotwater cylinder after showers.

[ralph t]

We have a Ruud Direct Vent Pace maker DV gas hotwater cylinder.It was installed three years ago.I have noticed that after four of us each have a shower in the evening a rumbling noise eminates briefly from the cylinder .Something I have not noticed before.I have assumed it is caused by water draw off and displacement by fresh water.The noise doesn't seem to happen when for example when the dishwasher or washing machine is used or there is ordinary use of hotwater taps.Any thoughts about causes?
Also how long do gas hotwater cylinders of the above kind last.? Ihave being informed no more than 10 years

 

[Softus]

Do you know the capacity of the cistern that supplies water to the cylinder? Is it possible that four showers are enough to drain that cistern?

If so, then this would result in air being drawn into the cylinder, and the rumbling could be the noise that the rising air makes.

You could easily prove this effect by having the first person to have showered, having dried themselves off, climb into the loft and watch the cistern while the fourth person has their shower

Regarding cylinder longevity, there are no rules. The big killers are scale (in hard water regions), flux deposits causing pinhole corrosion, and coil splits.