A bit more information is needed; is this a Moentrol or a Posi-temp valve? You will need to shut water down to the shower. If it is a Moentrol, it could be an issue with either the cartridge or the pressure balancing spool. If you are at least getting water, I am going to assume that it is a Moentrol. You will need to turn water off to the valve. Pull the cartridge and examine as to whether or not debris is blocking the supply holes of the cartridge. If your valve has built in shut off screws, you can slowly turn water on to clear any debris that may be inside the inlet port. I typically use a piece of PVC to go over the valve body so that water does not leak between the wall and the shower. Again, just turn water on enough to start it flowing. If you do not notice anything amiss with the cartridge, it could also be the pressure balancing spool. If that is on your valve, it will be a flat head screw about the size of a nickel. Water will need to be off for the removal of the spool as well. Again, you will be looking for debris that is blocking water flow. If this is an older Moen faucet, you may just want to replace the cartridge while you have it removed. If it is a push/pull, it is a Moentrol. If you have to turn the handle for water to come out, it is a Posi-temp. In my area, the cartridges run from $20-$40. However, Moen does offer lifetime on their cartridges. Lately, I have had a few more hoops to jump through to get the replacement cartridges from Moen, but they are still very pleasant to deal with.
Answers & Comments
A bit more information is needed; is this a Moentrol or a Posi-temp valve? You will need to shut water down to the shower. If it is a Moentrol, it could be an issue with either the cartridge or the pressure balancing spool. If you are at least getting water, I am going to assume that it is a Moentrol.
You will need to turn water off to the valve. Pull the cartridge and examine as to whether or not debris is blocking the supply holes of the cartridge. If your valve has built in shut off screws, you can slowly turn water on to clear any debris that may be inside the inlet port. I typically use a piece of PVC to go over the valve body so that water does not leak between the wall and the shower. Again, just turn water on enough to start it flowing.
If you do not notice anything amiss with the cartridge, it could also be the pressure balancing spool. If that is on your valve, it will be a flat head screw about the size of a nickel. Water will need to be off for the removal of the spool as well. Again, you will be looking for debris that is blocking water flow.
If this is an older Moen faucet, you may just want to replace the cartridge while you have it removed. If it is a push/pull, it is a Moentrol. If you have to turn the handle for water to come out, it is a Posi-temp. In my area, the cartridges run from $20-$40. However, Moen does offer lifetime on their cartridges. Lately, I have had a few more hoops to jump through to get the replacement cartridges from Moen, but they are still very pleasant to deal with.