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Old 05-22-2018, 06:57 PM   #1
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Tankless Water Heater and shower

We've been on the road for 12 days now and have no issues with our tankless water heater or shower. When running the shower, we just turn it on to full hot (shower valve all the way to the left as you face it) and the water heater was set to the temp we liked (104deg). No-muss / no-fuss. However, this morning, that didn't seem to work. When the shower was turned to full hot, the heater panel would only show the water getting to 92deg. If I slightly moved the shower valve back towards the right (as if mixing in cold water), the heater panel would move up to 104deg but the shower wasn't getting hotter because I was now mixing it with cold water. What the heck could be going on with this?
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Old 05-22-2018, 07:05 PM   #2
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Tankless water heaters are really suseptable to water pressure fluctuations. Good chance you had high water pressure
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Old 05-22-2018, 07:27 PM   #3
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Originally Posted by donniedu View Post
Tankless water heaters are really suseptable to water pressure fluctuations. Good chance you had high water pressure

That sounds like it might be right. The water gets hotter IF I turn the water pressure down with the shower valve. All the other faucets work fine. I'm just going to watch it and check tomorrow when we get to Glacier KOA.
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Old 05-23-2018, 07:02 PM   #4
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Seems it was just the water pressure that caused the issue. When we got to Glacier KOA today, I put on the pressure regulator and now the shower works fine again. Thanks for the help.
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Old 05-23-2018, 07:06 PM   #5
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I am thinking this is NOT water pressure. The tankless needs water flow which is caused by pressure. Mixing in cold water will actually decrease flow slightly. First thought is that your water going into the heater is very, very cold. Is this the case? There is a limit to how many degrees the tankless can heat the water.
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Old 05-23-2018, 09:25 PM   #6
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I am thinking this is NOT water pressure. The tankless needs water flow which is caused by pressure. Mixing in cold water will actually decrease flow slightly. First thought is that your water going into the heater is very, very cold. Is this the case? There is a limit to how many degrees the tankless can heat the water.
Not sure what the issue was, but we moved campgrounds today and we've got no issues here at Glacier KOA.
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Old 05-24-2018, 07:33 AM   #7
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Yes, ice cold water in the mid 30's makes the water heater struggle, even more in the winter when the combustion air is also very cold.


Using a pressure regulator may help but can sometimes cause the the water heater go into error mode due to a brief pressure drop below the threshold, best to open the shower valve slowly.


If the water isn't getting hot enough try to reduce the flow instead of mixing with cold water but be careful not to go below 0.5 gpm or else the water heater shuts down - a polar bear dip in the morning is not funny .


When running of the freshwater tank you eliminate flow and pressure fluctuations on the city water side, remember everybody in the campground uses the shower at the same time causing the water pressure to bounce up and down - not necessarily but it is possible.


If your water heater is a Girard Gen. 2 you can adjust the flow on the back of the heater, details can be found in the service manual or online.
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Old 05-24-2018, 08:14 PM   #8
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Fixed rise

Quote:
Originally Posted by donniedu View Post
Tankless water heaters are really suseptable to water pressure fluctuations. Good chance you had high water pressure
Tank-style water heaters provide water at roughly constant temperature, regardless of the temperature of the cold water coming in. Two factors keep them from being perfectly constant, but they are pretty close:
  1. Hysteresis of the thermostat. Heating stops when a set temperature is reached, doesn't restart until there's a few degrees drop (to keep the heater from cycling constantly).
  2. Flow in the tank is designed so that cold water entering at the bottom doesn't mix with hot water leaving the top, but it's not 100% perfect

On the other hand, tankless heaters (at least the ones in residential use) provide a constant temperature rise. You are expected to manually change the setting each spring and fall. If RV tankless heaters are similar, then consider what happens when you camp in the Rockies one night (overnight frost in August) and in the NM/AZ desert (100 degrees) the next night.

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Old 05-25-2018, 07:27 AM   #9
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Originally Posted by Larry-NC View Post
Tank-style water heaters provide water at roughly constant temperature, regardless of the temperature of the cold water coming in. Two factors keep them from being perfectly constant, but they are pretty close:
  1. Hysteresis of the thermostat. Heating stops when a set temperature is reached, doesn't restart until there's a few degrees drop (to keep the heater from cycling constantly).
  2. Flow in the tank is designed so that cold water entering at the bottom doesn't mix with hot water leaving the top, but it's not 100% perfect

On the other hand, tankless heaters (at least the ones in residential use) provide a constant temperature rise. You are expected to manually change the setting each spring and fall. If RV tankless heaters are similar, then consider what happens when you camp in the Rockies one night (overnight frost in August) and in the NM/AZ desert (100 degrees) the next night.

Larry
Correction. Neither are a constant temperature. Both Girard and my residential have a set output temp and the Girard will heat up to 70 degrees. If you set thermostat at 120 an inlet temp of anything above 50 will give you a constant 120. If water inlet temp drops below 50 the outlet temp will drop below 120.
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Old 05-26-2018, 08:34 AM   #10
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And this is exactly why I don't have a tankless water heater!! I've read so many posts on the idiosyncrasies of them when using them in RV's that until they get all the bugs worked our for RV's (likely not in my lifetime) I won't be switching over to a tankless. Now, we're going to have to hear from a host of people that swear by them, ugh! But the percentage of dislikes is high, and overall reviews are mediocre at best.
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