I am absolutely out of options here. My issue started a while ago, keep in mind this is a fully remolded house with everything new in it. The shower worked without issues for probably 6 months. The water pressure in my shower was slowly going down and down. For a while it was a bearable inconvenience , until It got so bad it had to be dealt with and eventually I am where I'm at now with no water at all int he shower. I turn the faucet on and all I get is some noise, like kind of a sucking sound, and a trickle of water. The shower is a Delta Monitor 13 series. The list of what has been done is fairly long:
Replaced the cartridge...twice, Ran without the cartridge to blow out any debris, Checked the lines and rough out for blockage. Had a professional plumber come out and check it. He cut out the tile, checked the rough out, pulled the pex lines off and they both ran fine disconnected. Checked under the house. After all that seemingly the flow was ok to the rough out he said it had to be the water heater, couldn't be anything else, because we checked everything. Its an on demand unit. He said that the pressure on the hot side must be down enough that the balancing valve was shutting the water down so it probably needed to be descaled. So fine.
Come to yesterday I do the descale. Still no water in the shower. At this point I have absolutely no idea what to do. I'm out of options here aside from ripping the whole brand new shower out or changing the brand new water heater out. Neither of which may fix the problem.
A word of note that I found curious in this whole thing. I've ran a cartridge with the guts taken out, the balancer and all that removed and also the plumber ran a test cap in place of the cartridge. I still got no water either time when that was done. I find that a bit curious since that is eliminating what is supposedly causing the problem.
A lot of people are stumped on this one here. Any ideas before I have to start getting drastic?