Happy New Year to all the Wallies..
I have a question regarding the replacement a Honeywell
3 Way mixing valve. How do you valve off the hot water supply from the boiler to the mixing valve? The cold water in has a shut off but I don't see one for the hot side.
The Valve is above the boiler.
That looks like a cut and replace. If there are no isolation shutoff's then you will have to turn off the boiler and the supply water and drain the boiler until the water level is below that of the valve.
Whats wrong with the valve??? I think you can replace the guts of these valves without cutting out the body. If you do go the cut route, you might want to replace the valve with the model that use threaded unions instead of IPS. If you ever had to remove it in the future, you wouldn't need to cut the pipes to get it out.
What is wrong with the valve? If it is non adjustable, you may be able to move the shaft manually, by removing the screw holding the gray cover in place. Using 2 wrenches, one on the body and one on the retaining nut, loosen the retaining nut slightly, this will allow you to turn the stem shaft. Once the shaft is loose, tighten the retaining nut, & replace the knob. It is a good idea to turn the shaft seasonally if not more often to prevent the shaft from seizing.
In the center of the cap there is a phillips screw. You will need to poke a hole in the label to reach it. When you remove the handle you can get to the stem retaining nut and remove the guts and replace with a new set.