Two newbie question for the experts, but here goes...

1. Under what circumstances do you use a SINGLE non-return valve, and when
do you use a DOUBLE non-return valve ? What advantages/disadvantages does
one have over the other ?

2. Whats the difference, apart from a few pennies, between an ISOLATING
valve and a SERVICE valve ?

Q1 is for a pumped hot-water loop, and the valve is to ensure water goes the
right way round the system ie preventing the fresh cold water entering the
loop from going the shortest way round the loop and bypassing the
thermal-store heater.

Q2 is just idle curiosity.

Thanks in advance
Ron Askew