I have a downstairs bathtub that does not have any hot water coming out of it. It is a single handle Moen faucet. The cold water runs through fine, but as I turn the handle all the way to hot, the water flow becomes a trickle, but will not get hot. It is a seldom used bathtub. All other bathtubs, faucets are working properly. Any help would be appreciated.

My thought would be that the cardridge in the moen faucet is stopped up with lime deposits and such that wash out of the water heater. The solution to this is to take the cartridge out of the faucet and if possible clean it and the holes in the faucet body that is still in the wall. If it looks like the cartridge needs replacing then I would replace it at this time. The cartridges are sometimes hard to get out but there is a tool at Home Depot and other places for this purpose.
I have another suggestion for you if you have someone to help you. While the cartridge is out have someone hold something in front of the faucet as you turn the water on, let it run for just a couple of seconds, you should get a full stream of water out of the faucet body, if you don't then the stopage is further back in the faucet or in the pipes leading up to the faucet.
Good luck. If you need more help just leave messages and tell us what you did and if anything changed.

Good morning Steven,

Letmetellu gave you very good advice and a place to start. Let me take it a step farther and walk you through removing a Moen Cartridge. Remove the insert button to expose screw.
Remove the screw and pull off handle assembly.
Turn off shut off valves underneath the sink.
Remove retainer clip (copper horseshoe shaped clip) and pull out cartridge with channel locks, pliers, or cartridge puller,(see image). Check the intake ports for blockage and open them up. If the valve is hard to turn on replace the cartridge. Do as Letmetellu advises and turn the water on and flush out the supplies. Before you reinstall the cartridge lube it with silicone jel and
Insert the cartridge with hole on the stem facing down in a tub/shower.
Reinsert retainer clip and screw in handle assembly, followed by the cap or insert button. Turn water back on. My company uses Moen valves on all their new construction. Moen makes a "cartridge puller", (see image) That will get those stubborn cartridges out of the valve body if you have a problem.

Now let's get to the root cause of your problem. The lack of monthly maintenance on your water heater.
For long life and fewer troubles you should keep your heater clear of mineral build-up by flushing on a regular schedule. Let me show you how. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Do this monthly to keep it clear. Now flush out your hot water lines on ALL fixtures. Now pull each aerator and clean the screens. Be sure you put them back togather the same way you took them out. Don't forget to flush it out every month. Your heater will thank you for it. Good luck, Tom

My moen single barmd new tub tap worked fine until I installed anew Noritz tankless.
When I have that one and only tap opened to it back feed/mixes cold into the hot water lines of the whole house.
Seems the pressure balancing tub tap does not like the pressure drops that the tankless does to maintain output temps.

Shut the water off and replace the cartridge. Moen will send you one for free under lifetime warranty, Contact them at;
Call: 1-800-BUY-MOEN (1-800-289-6636)
8:00 am to 8:00 pm Monday through Friday
8:00 am to 6:30 pm on Saturdays EST
Closed on Sundays and all nationally observed holidays.
To contact Moen Canada call: 905-829-3400

Clicking on;http://www.moen.com/consumersupport/installation/moen0133/moen0133.cfm
Will get you to a installation guide for replacing a Moen cartridge. When you have the valve open don't forget to turn the water back on for a moment to flush out the supplies. Good luck, Tom

Got a new Cartridge free from Moen... same problem called Moen they told me to go pound sand and that pressure balancing are not comp[atible with any tankless units... I want to start a class action lawsuit against Moen now. None of there products state this on there packages but yet they will tell you that on the help line after you have dry-walled everything... now I have to cut open a wall on a 22,000 reno just to change out the tub taps to the old style single for hot and cold.

How about it experts?
Will a Moen pressure balanced valve work with a tankless heater? If so then why not? Would the tankless kicking on be enough to confuse a pressure balanced Moen valve. How about other makes? Let's hear back from you!

Hi guys,

I've heard something about this awhile back...

In Mass, we aren't installing many of these because of the extreme temperature changes we can see up here. According to the pros around here, the tankless units have trouble in a lot of ways... ;)

I'd say that if Moen has said that its valve won't work with tankless units they won't work and Timdoe will need to replace the unit as he thought... UGH!

I hope MILO (plumbing expert) will pop in on this question as I believe he installs these and moen valves all the time. Where is Milo lately?

Good luck!

Mark