replacing mixing valve and purging

crabbydad

Taco mixing valve on my radiant heating is leaking and i am going to replace. My system has 5 zones, they all have a hose bib to use for draining,purging except for this one. My thought was to close off all the valve for the other zones and drain this one down using the drain at the bottom of the boiler, being careful to drain to just below the mixing valve so i don't drain the water from the boiler and the common return line. I will then purge this zone using the drain at the boiler. I figure i will have to purge all zones since i can't really isolate this zone. Does this sound like the best way to do this? i have the knob off the mixing valve, this zone is off and i had to close it slightly to stop the leaking. i tried working the valve in and out to see if this would stop the leak, but it didn't. this zone was off and the temps down so no overheated water went in to the radiant tubing.

hot_rod

I guess you do not have a valve above the pump? Too bad it looks like they were diligent about isolation around the valve itself.

I'd be inclined to replace the right hand valve with a Webstone Iso/purge valve if you have to drain down any ways. Then you would have an excellent purge point for that zone.

Add a valve
above the circulator also.

Purging through a 3 way is tricky as you never shut off the ports 100%

How many zones are being feed through the 3 way valve? Do they all heat under design conditions? There is a lot of pressure drop through that type of valve.

crabbydad

thanks for the reply

crabbydad

no valve above the pump. I like your ideas, they would make it a lot easier for any future repairs. this mixer only serves 1 zone which is the radiant in the floor of my kitchen and 2 small adjoining rooms. If i just opt to replace the mixing valve, would i use the valve on the boiler to purge this zone? and then purge all zones since i am purge thru lines that are shared by the other zones.

hot_rod

From what I seen that picture there isn't a way to assure good purge through that zone, without an additional valve.

A messy method would be to leave the pump flange loose, flow up the right side valve and allow flow to "spit" out until it runs clear. Not advisable.

Another option would be to put a Webstone purge valve flange above the pump. Flow would go up the right side pipe, around the zone, and purge from the new valve.

Is it all threaded steel pipe under the insulation? Removing the pump and adding a threaded Webstone iso purge valve there would be fairly simple, may need to shorten the pipe between the pump and mixers

You may get lucky, and be able to make the repair and fill and the pump could push the air around to the air purger, assuming you have one on the boiler?

There really is no substitute for a couple well placed valves to get a clean purge.