Overflow into F&E tank - why only intermittent

[Helg]

tried four (!!) plumbers on this, finally the overflow has slowed down to a trickle, just under a bucket in 24 hrs, for long periods no overflow at all
have traditional vented indirect system, small and large water tank
one cause for overflow could be that hot water is VERY hot, so I might have very hot water in hot water cylinder which then forces itself into small tank causing the overflow
so is excessively hot water the culprit? and why such a small amount of overflow and only intermittently?
Would it not have to be continous if there were a hole in coil through cylinder??

 

[picasso]

Why is your hot water very hot ? don't you have any controls over the temp? this is most probably your problem but a pinholed coil overflow depends on the height of the water levels in both the main and expansion tanks.

 

[Helg]

Thanks, only have thermostat on boilder (Ideal Mexico CF125, vintage 1987), water stays boiling hot even if stat on boilder down to 1-2,
onle plumber suggested putting in a new stat (if one can find it, only source seems to be ebay). Not sure his will do the trick.
No stat on hw cylinder
as mentioned, now overflow very intermittendly, nothing for long periods, but just under a bucket in 24 hrs

 

[jeff the gasman]

Could be ball valve creep or Boiler stat or pinholes coil. Or a combination of these.