Thread: Expected water loss from hot water system

you hws will discharge a little bit of water everytime it heats up
this is psrt of normal operation.

I'm not sure how much the temperatuce fluctuates with the gas water heaters, but with electric there is a heat, cool and heat again cycle of a few degrees even with no water use.

When heating there will be some water discharged from the relief valve. That will keep happening every heating cycle even if no hot water is used. When the tank cools and internal pressure drops, a small amount of cold water will enter from the mains. Simple expansion and contraction here and nothing magic.

I don't know the figures but 20mL doesn't seem at all excessive to me. If I had one of those water meters then I'd check mine but I would have guessed it would be higher than that. I suspect the gas heaters may fluctuate less (?) which would reduce the water loss through expansion and contraction.

Why don't you shut off the cold water feed to the HWS next time you go out for the day? This will tell you if the problem is the HWS or a leak somewhere else.

Mick

Originally Posted by Smurf

I'm not sure how much the temperatuce fluctuates with the gas water heaters, but with electric there is a heat, cool and heat again cycle of a few degrees even with no water use.

When heating there will be some water discharged from the relief valve. That will keep happening every heating cycle even if no hot water is used. When the tank cools and internal pressure drops, a small amount of cold water will enter from the mains. Simple expansion and contraction here and nothing magic.

Thats exactly what I think it is. 20ml seems about right. Probably more to do with the expansion/contraction of the water cylinder is it cools down thus allowing a little more water to trickle through. I had a shower about 30 minutes before I read the meter. So by the time I read the meter, I assume the HWS was fresh from a heating cycle.

In fact, I calculated that the water cylinder diameter would have to increase by a fraction of a mm (around 40 micron) to accommodate an extra 20ml. It would bulge in the middle meaning that it would probably be about 120 micron in the middle...about a growth of the thickness of a hair in radius....

Hmmm.. maybe I spend too much time thinking of this kinda stuff...?

Originally Posted by Gooner

T I had a shower about 30 minutes before I read the meter.

You need a hobby, try woodwork..