Cold showers: cold water crossover or bad TC in heater?

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Jbrk

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Sorry, this is a long one. I have an interesting problem and thought I'd post up here to ask the community.

Problem: hot water isn't getting hot enough at taps... Intermittently. It's obviously a problem for showers. just randomly started happening maybe 3 weeks ago. It's intermittent yet seems to be getting worse.

Background: HTP rgh-199 crossover wall hung water heater. This thing is apparently smarter than I am. Even the techs at htp don't even know how it works. The input is 1" from the city, pressures hover around 80psi. the output is 1" risers serving 3 floors plus basement. Each floor has a manifold close to the fixtures with 1/2" branch lines to each valve. All the valves are single stick left hot/right cold ceramic cartridge style (see photo). Except, there is a washing machine on the 2nd floor that has regular hot and cold taps.

When the issue happens, water coming out of taps are around 100F, when the water heater is set to 140F. The heater has a thermocouple at the outlet which you can read on the LCD from the secret menu, which is reading 140F. I also have a tridicator downstream of the heater which also reads 140F (it used to be down stream of the tempering valve, but I ripped that out in frustration)

I attached a crude riser drawing. I'm sorry for my bad drawings skills. But you'll get the gist of it.

At first, as a temp fix, I maxed out the water heater output to 160F. It seemed to work at the time, but now it continues to sometimes work, I've left and the clients are still complaining of not hot enough, which is around 100F.

freakin’ baffling to me. Hopefully someone on here has some insight to share.

Problem solving:
So in my mind, I've widdled this down to 2 things. It's either the water heater, or cold water is getting into the hot line somewhere.

The water heater is not faulting, its all clean in there as its a new unit and probably 3 months in use before this issue started. No intake blockages or anything, although it would fault if anything like that was wrong, like low gas pressure, low water pressure, not enough intake etc. At first I though maybe the intake or output thermocouples are giving false readings... Does that happen? Like it still gives readings so the system doesn't fault but the TC becomes miscalibrated mid use?

The other thing I can think of is one of the valves is crossing over. That's what I thought was happening with the tempering valve, So I pulled it out. But I can't imagine one of those would cceramic cartidges would cross over THAT much water? looking at the cartridge, the only place cold water can cross to the hot is from that little gasket as the back, if the gasket failed, sure some water could get through, probably make a lot of noise at the valve, or get water leaking out the outlet right?

I'm out of the country now, and trying to problem solve this. Any other possibilities someone else can think of? Before I send someone in there on a wild goose chase running hoses off washing machine taps and feeling pipes.

Thanks
 

Jbrk

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Reach4

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The other thing I can think of is one of the valves is crossing over.
Close a stop valve for each thing that has a stop valve. See if the problem gets better. If no stop valve, run the problem water. Feel which no-stop-valve lines are not room temperature.

It would be useful to put a pipe thermometer on the output from the WH.
 
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Jadnashua

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If you don't have a stop at each valve and the valve allows you to turn it to full cold while off, try that. It sounds like there's a cross-over somewhere. Finding it is a process of elimination.
 

Tuttles Revenge

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Could the water heater be overwhelmed? 140 is really hot for an on demand. Some just throttle down the output to reach that temp.. some just give up trying. I'm not familiar w/ that model myself so just throwing it out.

crossover can happen too when a client changes out their shower heads and installs something with a stop valve on a pressure balance system.
 

Jbrk

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Could the water heater be overwhelmed? 140 is really hot for an on demand. Some just throttle down the output to reach that temp.. some just give up trying. I'm not familiar w/ that model myself so just throwing it out

Nah, I tested that. This model can go up 160F if you change a setting in the secret menu. To simulate max demand I took the T&P out and threaded in a ball valve that I could easily play with Flow and look right at the unit. At 160F it can handle max 6.5gpm of flow and it will dial back the flow to maintain the temp. (sorry Dana, I didn't get a temp on the incoming So I can't state the delta T)

Assuming that 140F will allow greater flow capacity, a shower head should be fine. Unfortunately I didn't get a chance to measure the flow of the shower heads. But the sink faucets are 2.2gpm. Assuming same or less for a shower head,there should be plenty of capacity.

I'm going to talk my guy through a crossover test tonight. I'll report back.
 

Jbrk

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Ok I think I got it solved...

The issue, and this is my fault for several reasons.

I had roughed in 2 shower heads and 2 faucets in the basement for a future bathroom and have threaded plugs on the outlets. They're the same valves, with the ceramic cartridge lefthot/rightcold and pull up to open as the upstairs ones.

Just Before the drywall boarding got started, the supply lines ball valves were opened at the manifold and the shower/faucet valves themselves were opened to pressurize the outlet lines. this was done in case the drywallers sunk a screw into the pex so that everyone would know (and they did several times).... Well the protection caps got placed back on the valves.... While they were OPEN, and they hadn't got touched since. So basically there is 4 open paths of cold water coming into the hot line through the valve bodys and diluting the hot water temp via the open valves in the middle position.

Pretty wild, and innocuous... I'm disappointed I didn't think of it earlier. I spent so much time on it haha. Live and learn.
 

Tuttles Revenge

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Yep.. been there.. We generally install rough in valves with stops, so one side can be shut off to prevent cross over. Or by removing the cartridge and replacing it with a plug made for that valve.
 
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