How can I flush my water heater when the edge of the drip pan partially blocks the drain valve?

Personaly I'd Follow Joe - Call A Number Of Plumbers And Tell Them Your Problem (Need The Drain Pet-cock / Valve Truned To One Side) Get A Estimate Of The Cost - Check With Friends / People At Work / School Mates / Etc. For A Plumber They Would Recommend - Local Chamber Is Also Good Help... I Have A 6 Year Water Heater Going On 14 Years - Drained Every 3 Months. I Turn Off The Cold Water Feed - Open Drain Valve And Pressure Relief Valve Lifting The Little Lever (On The Top Of The Tank) +/- Lunch Time - Close Drain Valve - Lesson For Water Entering The Heater And Youll Hear A Different Sound When It's Full / Almost Full. Close Pressure Relief Valve. You Should Hear No Water Movement. Turn Electric Back On Water Is Hot For evening Baths... I Would NOT Recommend Opening Down Stairs Faucets, That's A Lot Of Climbing. And They The Faucets Shouldn't Have Any Sediment In Them Anyway. BUT, It Is A Good Time To Check You Aerators

Think before turning that drain valve open, they usually will not shut off if thay are over 4 yrs old, or not brass drains , i have changed over 500 water heaters

When the plumber installed my hot water heater, the drain valve and drip tray interfered with each other, same as yours. I had the plumber turn the valve sideways to solve that problem. I don't know if that will work in your situation, though.

I can't believe a plumber would set up a heater in such a way that you can't get a hose on the petcock. I think the only way possible is to cut the drip pan and attach a hose and proceed to drain the unit. After the tank is drained, you might be able to place a new drip pan if you had some help. I would turn off the power to the heater and continue using hot water until it eventually runs cool. Then shut off the supply water to the unit and turn on a hot water faucet to take the pressure off the unit. Then you can just open the pressure relief valve and the water should drain freely through the hose to outside. Good luck!