Coil inside cylinder

[Vicario]

My hot water tank (fed from a Baxi back boiler) has been in the house longer than me (30 years plus).
I know that eventually these develop a fault whereby the coil starts to leak and 'boiler' water gets into the hot supply. Just wondering if I should wait for this to inevitably happen or whether it's worth getting a new one now. How would I know if the coil was leaking - presumably the hot water would turn a different colour.

 

[kevplumb]

How would I know if the coil was leaking - presumably the hot water would turn a different colour.

if it was leaking you would have an overflow running

 

[Goldspoon]

If it were to happen then one of two things happens:

1. Water from coil enters cylinder.
2. Water from cylinder enters coil.

Which one?

Depends on water level heights in the two cisterns that feed them (usually in loft).

If small F&E tank is higher then yes, dirty water enters clean.

 

[Goldspoon]

How would I know if the coil was leaking - presumably the hot water would turn a different colour.

if it was leaking you would have an overflow running

Most likely yes but not always the case Kev...? If water levels in F&E and CWSC are very similar then they can level out and still not reach an overflow.

 

[Onetap]

I had such a leak in my house, when I bought it, from the heating system into the hot water system. The heating F&E tank was mounted above the cold water storage tank; the rate of leakage was so small that it never reached the overflow and the water was drawn off during the day. There was no sign of discolouration in the water because it was greatly diluted.

I didn't notice until I did the first of many amendments, putting the heating F&E tank on the loft floor. That night I was woken by the overflow dripping. A new cylinder was installed the next day. There were other indications of a leak, i.e., the cold feed connection to the heating was blocked solid with limescale.

Old cylinders usually had a much shorter internal coil than modern British Standard cylinders; it would be worth replacing the cylinder even if it doesn't leak.