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Old 12-05-2021, 02:39 PM   #1
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Tankless Water Heater

I recently installed a tankless hot water heater that is a 4.8 gpm heater and I have a Sea Flow 30 psi 3 gallon per minute pump with a variable pump speed . since Iíve installed it trying to take a shower has been difficult because unless I run the faucet in the bathroom or slightly when Iím taking a shower I donít get any hot water to the shower . So I wonder If installing an expansion tank would actually help me so Iím thinking if I turn on the hot water then the expansion tank will fill up with water . Now before or after the hot water heater Iím not sure Would be the best option? I think because I use a pushbutton showerhead so that water only comes out when I push the button on to save water it causes a pressure loss . but trying understand the problem I held the button for like 5 min and the tankless never sparked . Only until I run the faucet nearest the shower will it kick on . This defeats the whole purpose of the push button shower head . so Iím wondering what anybodyís feedback is on this
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Old 12-05-2021, 03:09 PM   #2
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Shower flow is restricted therefore the required Flow for Tankless operation is NOT being made hence the need to open bathroom sink faucet

Remove flow restrictor in shower .....either in end of hose where it connects to shower faucet, in end of hose where it connects to shower handle or in the end of shower handle
*Some are NOT removable.....so use 1/4" drill bit and enlarge the opening (increases flow)
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Old 12-05-2021, 03:59 PM   #3
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Quote:
Originally Posted by Christian007 View Post
I recently installed a tankless hot water heater that is a 4.8 gpm heater and I have a Sea Flow 30 psi 3 gallon per minute pump with a variable pump speed . since Iíve installed it trying to take a shower has been difficult because unless I run the faucet in the bathroom or slightly when Iím taking a shower I donít get any hot water to the shower . So I wonder If installing an expansion tank would actually help me so Iím thinking if I turn on the hot water then the expansion tank will fill up with water . Now before or after the hot water heater Iím not sure Would be the best option? I think because I use a pushbutton showerhead so that water only comes out when I push the button on to save water it causes a pressure loss . but trying understand the problem I held the button for like 5 min and the tankless never sparked . Only until I run the faucet nearest the shower will it kick on . This defeats the whole purpose of the push button shower head . so Iím wondering what anybodyís feedback is on this
There's a thread here: https://www.irv2.com/forums/f258/tan...-475585-4.html where there's a discussion of tankless water heaters. As I read that thread, there doesn't seem to be a ringing endorsement of the concept in a typical RV installation.

There's a concept of a "cold water sandwich" that's described here: https://www.efficientsystems.net/blo...fect-solution/
that might help you understand the challenge and possible solution.

Take care,
Stu
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Old 12-05-2021, 04:14 PM   #4
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Quote:
Originally Posted by Old-Biscuit View Post
Shower flow is restricted therefore the required Flow for Tankless operation is NOT being made hence the need to open bathroom sink faucet

Remove flow restrictor in shower .....either in end of hose where it connects to shower faucet, in end of hose where it connects to shower handle or in the end of shower handle
*Some are NOT removable.....so use 1/4" drill bit and enlarge the opening (increases flow)
Bingo!
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Old 12-05-2021, 05:55 PM   #5
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Expansion tank is NOT going to increase flow thru your shower
Expansion tank helps limit pump run time but does not increase flow
Pump gpm rating, pipe size and ANY restrictors affect flow

You shower has restrictor that limit flow
Either remove/increase size for more flow OR turn on bathroom sink faucet......One or other will allow adequate flow to star the heating cycle on that Tankless WH
*must meet flow requirements before it will fire up (safety feature)
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Old 12-05-2021, 06:04 PM   #6
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Hi ! Welcome to IRV2! We're sure glad you joined us!

Have fun and keep her between the ditches!

Good luck, happy trails, and God bless!
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Old 12-05-2021, 06:38 PM   #7
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Need a bit more flow as mentioned above.

As far as shutting the shower head down to save water, each time you do that, expect a blast of cold water.

The coils in a tankless heater are super thin so they can transfer heat to the water fast. Because if that, the water cools real fast too.

There is also a delay in firing up the burner letting cold water thru.

I turn on the hot faucet only and take a high speed shower. The wife shuts the water down and aims the water away when she turns it on, until it warms up again.

One other thing, if your on city water and use a regulator or restricted filter, try with out.

Could also try leaving the pump on. On mine it boosts bad flow from some camp grounds.
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Old 12-05-2021, 06:46 PM   #8
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Quote:
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Need a bit more flow as mentioned above.

As far as shutting the shower head down to save water, each time you do that, expect a blast of cold water.

The coils in a tankless heater are super thin so they can transfer heat to the water fast. Because if that, the water cools real fast too.

There is also a delay in firing up the burner letting cold water thru.

I turn on the hot faucet only and take a high speed shower. The wife shuts the water down and aims the water away when she turns it on, until it warms up again.

One other thing, if your on city water and use a regulator or restricted filter, try with out.

Could also try leaving the pump on. On mine it boosts bad flow from some camp grounds.
That is because Pump is supplying the demand....
Check Valve in City Water Inlet closes when Pump Runs
Pump will only run if City Water pressure is lower than pump start set point
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Old 12-05-2021, 07:17 PM   #9
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Ok this My theory. So the expansion tank fills up and is pressurized against the tankless by putting it before the tankless and every time I press the shower button Im releasing that diaphragm pressure maybe 30psi that would otherwise be diminished because I normally have a variable pressure pump behind the tankless . So now maybe 2 gallons of pressurized water 30psi instead the lower flow of the usual VSP is flowing. It seems to follow that pattern because the tankless kicks on when the faucet is fully open demanding a higher pressure value �� IT would seem. Because now instead of the pumping sensing a lower demand because the lack of outgoing pressure to shower the demand is higher to fill the expansion tank . Sort of substitution is going on. But then I’m thinking when the expansion tank is being relieved of pressure how fast will the exchange be of new repressurization . That might work out ok considering that would be the time I’m using soap. Lol I smell an experiment muaahaha�� oh and I’m completely off grid no city water. And thank you everyone for answering and trying to help me . Life gets messy and then you get bizzy.
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Old 12-05-2021, 07:57 PM   #10
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I believe that the tankless water heater is triggered (fires) based on water FLOW, not pressure. Your problem lies in the fact that you're not demanding adequate flow for a long enough period to meet your desire for hot water.

Until FLOW (related to pressure, but not the same) thru the water heater meets the water heater set point, the water heater will not trigger.

Your on/off switch in your shower exacerbates that problem. Whenever you turn your switch off, there's no FLOW and the heater turns off. That's what causes the "cold water sandwich". Whenever you turn the switch back on, there's a slug of cold water in the line that reaches your shower before any hot water arrives.

Also, if your shower uses a mixer valve (single water handle to control temperature vice two separate - one HOT - one COLD handle), your single handle mixer valve is asking for both hot and cold water. Perhaps as much as half of the FLOW to your shower is a demand for cold water.

Take care,
Stu
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Old 12-05-2021, 08:02 PM   #11
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Your theory is wrong

Pressure vs Flow
Expansion Tank provides increase in pressure & Volume
Tankless WH operates off FLOW

But that has been explained already.............
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Old 12-05-2021, 09:25 PM   #12
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When you get your shower head flow increased and things are working well, here is a device that let's you leave the shower running and not waste water.

You divert the hot water back to the tank, instead of stopping it and letting it cool.

The trick is getting a return line from the shower wall back to the tank.

https://aquaviewinc.com/rv/
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Old 12-06-2021, 03:16 PM   #13
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So, the link to explain the "sandwich" effect says to install a 6 gallon water heater. I already have a 6 gallon water heater in my TT. What would the purpose of the tank less water heater be?
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Old 12-06-2021, 03:35 PM   #14
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So, the link to explain the "sandwich" effect says to install a 6 gallon water heater. I already have a 6 gallon water heater in my TT. What would the purpose of the tank less water heater be?
For a regular tankless water heater in boondocking situations the purpose is to spend a bunch of $$$$ for a frustrating hot/cold sandwich shower and use/waste more water.

We just heat up the water heater to shower temp and run it straight at the shower, no blending. DW and I can both shower from one round of heating with our 6 gallon water heater.
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