Cold water tank filling too slowly

Are you sure that the limiting factor isn't the flow rate of water from the mains?

You can work out the max flow rate very easily by measuring the time taken to filll (eg) a 5-litre bucket in the bathtub (it will be slower still up in the attic.

Then how long does it take for the tank to refill when it's completely empty, and no other taps are in use? Compare the two figures and that should give a hint as to whether the water supply is being throttled at the tank inlet.

You could always add a second cold tank in parallel with the original, or replace the original with a bigger one? However I'm also wondering how big your hot water cylinder is - if it only contains 25 gallons of hot water (which is quite likely), it isn't going to help much if you prevent the hot tap running dry, only to have cold water emerging instead!

There was a sort of ribbed/threaded insert that came with the two Torbecks I fitted, to be cut to length depending on the supply pressure. Did you by any chance fit the whole insert?

I had the same problem and solved it by adding a second Torbeck valve.

Overall, it made about a 30% improvement to the flow rate.

I adjusted the float on one to be lower than the other since there is no need for both to open unless a lot of water is being used.

When filling the bath, the bath cold tap will get priority (being at a lower altitude) over the cold tank, preventing it being rapidly refilled. You may find a 50 gallon tank is more appropriate. 25 gallon tanks are really quite small.

You might also want to check the adjustment on the valve. You may find that the water is being shut off too early and you are only storing 15 gallons or something. Also, check the fill valve for any flow restrictors. You may improve matters by removing them.

Christian.