setting correct water level in CWSC and F&E Cistern's?

[londonboy123]

what are the best levels to set the water in both cwsc's and f&e cistern's?

I know that both by building regs should be a min of 25mm below the invert of the warning pipe, but that is when heated! Is there a general rule of thumb to use when setting both?

 

[ChrisR]

Not that I know of.
I'd allow a lot more than that, for no particular reason!

People get het up about the expansion of the water in the F&E tank, but at about 3% of system volume it's only going to be a couple of litres. You don't need much in there, so 1/3 to 1/2 full is fine.

If a washer starts to cause a drip in a CWSC it would come out of the overflow, sorry warning pipe, much more frequently if the level is higher. Good thing or not??