New valve - shower getting hotter?!

[stangel]

You may have seen my earlier post about repiping my shower: http://www.plumbingforums.com/forum/f9/need-advice-shower-repipe-519/

I've now got new copper pipe from under the house, plus a new Delta universal valve and fixture. The problem is that the shower is gradually getting hotter! Over the span of about 5 minutes, it keeps getting hotter and I have to turn the water colder and colder, until it gets to the point that the tankless water heater shuts down. Then I have to turn the heat back up, and the cycle starts over again.

Here's the trim / cartridge in use: Innovations Monitor® 17 Series Shower Trim : Bath Products : Delta Faucet

I contacted Delta, and they said my tankless water heater needs calibration. There really isn't any calibration on it -- it's got a digital temperature selector, that's set at 120 degrees. It's a Bosch GWH 2400 ES: Features and Specs for the Bosch GWH 2400ES Tankless Water Heater

Water pressure and flow are good, and I did make sure that the cartridge is not installed backward. Anyone have any ideas here?

thanks very much,

Mike

[havasu]

I can't help much except the water heater calibration stuff is bull. Either the faucet scald protector is not adjusted correctly or installed backwards, or your valve is bad.

[phishfood]

Actually, I would lean toward the water heater. Not that a tub valve is incapable of creeping, I have seen that happen before. The anti-scald systems that I am aware of work off of pressure, so the only time that they moderate temperature is if the pressure coming into one side of the valve is lowered. But if the temperature of the hot water supplied to the valve is changed, than the temperature of the water the valve puts out will still chamge.

I am outside of my area of practical knowledge when it comes to tankless water heaters, though. Hopefully Reedwalker will check in.

[stangel]

Originally Posted by phishfood

Actually, I would lean toward the water heater.

You may be right -- I did a little test this morning: once I got to the point where the valve was almost all the way cold and yet the water temperature was still too hot, I pushed the valve all the way to hot -- the water got scalding hot and measured over 130 degrees (even though the tankless heater is set to 120).

Checking the troubleshooting section of my heater manual, it appears that restricted flow can cause this problem. I see three possible explanations:

1. The filter screen needs to be cleaned (possible due to sediment getting knocked loose as I had the house water on and off several times)
2. The heater may be due for descaling (I do have high mineral content in my water), or
3. The new pressure-balancing valve and shower head may be restricting the flow more than the old system.

I'll report back after I've looked into #1 and #2. :-)