YUP.. it's a moen.
Most likely there is something blocking the cartridge or the hot water inlet to the shower valve
Here is a couple pictures that should help you to iron this out.
Click on:
http://www.moen.com/shared/pdf/L2353pt.pdf This one has some extra parts the older model doesn't... just keep track of how they line up to everything and should be fine.
Click on
attachment: moenparts2.pdf at lower left also.
Follow basic guidelines below, but work with picture that resembles the parts in your faucet.
Basically, need to shut water off to valve, then remove face plate, handle, and chrome sleeve (just pulls forward). Then will need to pull up on the copper clip you see sticking up (I use needlenose pliers), then pull the entire moen cartridge out... give a good yank on it (hold against valve body when pulling) with pair of pliers (or attach handle back onto cartridge and pull that). At this point,
put rag over valve and PULSE the water real quick on/off to clear faucet of any sediment that may be in there.
This is also when you confirm that hot water is getting into the valve....so have a friend pulse that water while you keep rag over it..see if water comes in through both inlets (if can pulse individually (hot and cold water ) even better). If hot water doesn't flow into valve then may need to probe the inlet a bit.. or may need to follow hot water pipe down to the nearest shutoff and investigate that next.
Then, I would just go to home supply store and get a replacement cartridge... could get the MOEN replacement or the universal replacement... both will work here.
Also pick up a little plumber's grease or silicone grease.
Then grease the orings around new cartridge, install (wiggle it a bit) cartridge.. push it in REAL TIGHT... then install copper clip back in place (align both sides of clip, and push down/in... may need to TAP on clip to set it down in place again).. then replace trim and test away. That should do it for you.
NOTE! Moen has a lifetime warranty on parts... call 1800BUYMOEN, tell them the part you need (see my pic. Will tell you cartridge numer) and they will ship it to you for no charge (includes free shipping)... BUT you will need to wait 10 business days to get it! Or you could pay $12.00 and they will ship it 2 day!
Or, if in hurry, just go to home supply and pick part up.
Moen also has an online tutorial to assist you further (just read carefully)... click on:
Installation Help / Animated Tutorial - Installing the Moen 1225 / 1200 Cartridge
Hope that fixes all for you.
Let us know how it goes.