I have a small leak above one zone valve, (2 are on system) I am assuming this has to drained before any attempt to solder(suggestions) will this do anything to the zone valve ?, and should I use map gas or propane seeng as when doing this. When drained and refilling is ther anything else I should be cautious about, and how would I bleed air after completion, thanks for any advice.
Where is the leak coming from? If it's coming from the soldered connection on the ZV then there may be more to it then just a bad solder joint (unless you KNOW this is what it is).
It could be that the copper has worn thin and now had a pin hole leak in it etc.
You need to sweat copper out of the zone valve and inspect it.
Drain all water from the system. When you refill you need to bleed the air off through the bleeder valves located on the rads (some will have one some won't).
If you're not that comfortable with these systems etc I would strongly recommend you hire a professional.