Looking for a little advice

Suspect problem with my Aqua-Gard Mixing Valve Model ZW1017.

System age 6 yrs.
All hot water outlets produce varying temps. (lukewarm to hot)
Temp adjust on the mixer has been turned as far as I dare towards hot – any more, I fear it will pop out completely !
Hot water heater is not an issue (its producing)
The specs page (http://content.zurn.com/web_documents/pdfs/installation/ISZW1017.pdf)
Suggest it may be fouled with debris

Here is my action plan
Shut off water supply and HW-tank
Open 1 or 2 faucets to drain the taps
Remove the mixing Valve
Flush the valve out with water
Reinstall using plumbers tape on the threads
Turn the water on a pray

Questions:
Am I missing anything in my plan?
How much water spillage can I expect when I remove the Mixing valve?
The position of the valve is directly above the HW-Tank
Is the hot water tank pressurized? Do I need to drain the HW-tank?

When you have the valve out for flushing you should also turn the watrer back on at the main supply for just a brief moment to flush the lines, this takes two people. One person opens and closes the supply while the other person holds a towel over the open valve body

Good Idea, Thank You ;)

If you are finding that most of your fixtures run hot BUT your showers and/or tub/shower units are running less hot then you may have tub/shower valves that have temperature limiting devices (TLD) installed under the trim somewhere (could be under handle or under trim plate). These TLDs are adjustable and are usually easily accessed. I would get a cheap water thermometer (sold at all home improvement stores) and take temperature readings at the kitchen faucet and then at the tub/shower valves if this sounds like part of the problem. If you are getting hot water at any fixture in a regular way but not others then the issue should not be the mixing valve.

Back to you...

Mark