Tankless water and water miser valve.

[Weissj62]

I have a Miramar 37.1 with a tankless water heater and the water miser valve in my showers.
Heres my problem, when I'm in the shower running water through the shower head everything seams to be working OK until I turn the water miser valve to recycle the water while soaping up.
While recycling the water, the water heater will overheat until I switch it back to flow through the shower head. And boy oh boy, don't stand under the water or prepare to get basted.
Has anyone had this problem and if so, what's the fix?

 

[Chateau_Nomad]

I have a ShowerMiser with a tank heater, but my "process" may work for you as well.

First I installed a positive OFF valve on the shower... I replaced the "trickle off" - which sort of stops the water, but still allows a dribble. I wanted a POSITIVE OFF with no dribble. This is where the shower hose connects to the faucet.

For temperature adjustment at the beginning of the season I turn the hot knob on full, then add cold as necessary to adjust. Then we turn the water on/off using that positive OFF valve.

Essentially we rarely touch the hot/cold knobs once they're set... we turn off the water with that ON/OFF valve.

So... getting ready to get in the shower, that positive valve is OFF, and the ShowerMiser is set to recirculate... this is essentially the equivalent of having the faucet handles closed when not showering.

Turn the positive valve ON allowing water to flow from the hot water tank... it takes about 10 seconds or so to get to temp. By then I'm in the shower... open the ShowerMiser valve. Get nice and wet.

When ready to soap, I close the positive OFF valve, then turn the ShowerMiser valve to recirc. No water is now flowing.

When ready to rinse, open the positive OFF valve - which is now again letting water recirc to the freshwater tank. After a few seconds, open the ShowerMiser to start the shower again.

Rinse... repeat.

It's really not as complicated as it sounds AND it should give the full flow needed for your tankless heater.

This has worked great... no blasts of off temperature cold or hot water... and no wasted water waiting for up to temperature.

 

[Bob Nodine]

I have a Miramar 37.1 with a tankless water heater and the water miser valve in my showers.
Heres my problem, when I'm in the shower running water through the shower head everything seams to be working OK until I turn the water miser valve to recycle the water while soaping up.
While recycling the water, the water heater will overheat until I switch it back to flow through the shower head. And boy oh boy, don't stand under the water or prepare to get basted.
Has anyone had this problem and if so, what's the fix?

I suspect something is not plumbed correctly. When you put the hot water system in by-pass the flow thru the tank should continue as if you had the shower on and the temperature of the water should remain about the same. Now if you are mixing cold water at the shower then all bets are off. It is best to adjust the temperature of the water heater to be comfortable without mixing cold water. Leave the cold water off and use only the hot water.

 

[Chateau_Nomad]

What Bob said, especially about setting the temperature. He makes a good point, because if plumbed properly it shouldn't make any difference in flow.

Technically I could just use the ShowerMiser without the shutoff. But depending on length of shower, (if on propane) you could waste a lot of propane running hot water back into the freshwater tank.

 

[Weissj62]

What Bob said, especially about setting the temperature. He makes a good point, because if plumbed properly it shouldn't make any difference in flow.

Technically I could just use the ShowerMiser without the shutoff. But depending on length of shower, (if on propane) you could waste a lot of propane running hot water back into the freshwater tank.

Thanks Chateau and Bob.
To add a little more detail, my water miser valve does give me the option off stopping the flow to the mixer valve but that also turns off the tankless water heater which allows the water to cool in the lines and waist the amount of water that it takes to get back to temp. Which is what this water miser valve is supposed to prevent.
That said, when I have full hook up options, that's not much of an issue. But when boondocking, water waist becomes a problem. Especially when the whole 7 member family is on board.
To Bob's point, I do set the temperature to a comfortable hot point so there is no mixing of cold and hot because that never works either. Too much turning on and off of the water heater which also is not fun while in the shower.
That opens up another sour point with me. I am constantly changing heater temps during to day.
When someone wants to shower, I turn the temp down, when washing dishes, I turn it back up. Now add the fact that there are 7 members on board and it can get challenging for everyone to remember to adjust the water heater.

That said, I am under the impression that the heater does not turn on unless there is water flow through it.
So if the water is flowing through it at a rate that keeps it working, why does it overheat vs maintain

 

[Chateau_Nomad]

You aren't wasting water... it's recirculating back to the freshwater tank. Even if the water cools, just recirculate water back to the tank until the hot water from the heater reaches the shower again. The only thing "wasted" is the small amount of propane to reheat the cooled water.

 

[16ACE27]

Thanks Chateau and Bob.
To add a little more detail, my water miser valve does give me the option off stopping the flow to the mixer valve but that also turns off the tankless water heater which allows the water to cool in the lines and waist the amount of water that it takes to get back to temp. Which is what this water miser valve is supposed to prevent.
That said, when I have full hook up options, that's not much of an issue. But when boondocking, water waist becomes a problem. Especially when the whole 7 member family is on board.
To Bob's point, I do set the temperature to a comfortable hot point so there is no mixing of cold and hot because that never works either. Too much turning on and off of the water heater which also is not fun while in the shower.
That opens up another sour point with me. I am constantly changing heater temps during to day.
When someone wants to shower, I turn the temp down, when washing dishes, I turn it back up. Now add the fact that there are 7 members on board and it can get challenging for everyone to remember to adjust the water heater.

That said, I am under the impression that the heater does not turn on unless there is water flow through it.
So if the water is flowing through it at a rate that keeps it working, why does it overheat vs maintain

If you are mixing the hot and cold water perhaps the Shower Miser is plumbed so it only recirculates the hot water and the cold water is "shut off". So when you resume you get that blast of fully heated water before the cold is mixed back in.

 

[Weissj62]

Thanks again Chateau.
I think I understand what you mean now.
So I should switch the miser valve to basically off position, soap up, switch to recirc to heat the water, then switch to shower, correct?
This might work for adults but could be challenging for the younger kids.
The bigger question is still, why does the water heater overheat vs just maintain temp when recirculating water?

16ace27.
Even if it is only recirculating the hot, I would think it should still maintain set point temps vs overheating the water heater.

 

[Chateau_Nomad]

Try some of these suggestions, then please report your findings. Several folks have had similar issues - maybe your trial and error tests will benefit someone!

Also if you can tell us how your setup is plumbed - is just the hot routed back to the freshwater tank? Both hot and cold? Is the recirculating line from the ShowerMiser dumping directly into the freshwater tank, or is it plumbed to the suction side of the water pump? Thanks!

 

[Weissj62]

Hello again.
So here is my setup.
The water (hot and cold) come up to the mixer valve, then below that is the water miser valve that has 3 options, to the shower head, off, or recirculate.
It will recirculate whatever you set the mixer valve to. Hot and cold. (I have my faucet set all hot with water heater set to 103F).
The recirc water does not go back to the tank. It goes back to a manifold (I have 2 showers) and then to the pump again.

I have done the off, then recirc, then to the shower head trick and that works as long as I don't leave it recirc for more the 45 seconds. (Thats about how fast it starts getting to hot and soon after overheats).

I could continue to do this, but it is my nature to find and fix the issue vs doing something I shouldn't have to to get by.

Today I did some testing.
I turned on the shower, flipped it to recirculate and also turned on the faucet for the sink and watched the heater temp reaction. This aloud more time before the water heater overheated but it really didn't do much for finding a resolution for my problem.
My thought was maybe it had some air that the sink faucet would purge out. No luck.
Now I'm wondering if my pump pressure is set too low and just not moving the water fast enough?
Does anyone have a good way to test the water pressure from the pump? Maybe an inline pressure gauge?
Or maybe add an accumulator tank for holding pressure longer to rest the pump?

 

[16ACE27]

So if the hot water is not going back to the tank, but to a suction manifold where it is pumped back through the water heater and the water heater heats it again without sensing the temperature, wouldn't the hot water now coming to the shower be just as hot?
This is what makes sense to me.
What, in the water heater, controls outlet temperature?
Whay would the water coming out of the water heater be scalding hot (instead of 103 degrees) unless the temperature controlling circuit was faulty?

 

[Weissj62]

That is what I have been trying to figure out.
The weird part is, when NOT going through the recirc path, it holds temperature at the set point pretty well with both city or on board fresh water. As long as I'm not mixing any cold water that is.
If I try to raise set point and mix any cold, the pump cycles on and off causing the pressure/flow to drop which in turn, turns off the water heater. This is what makes me think my pump may be weak.
Anyway, I would think that whatever is making it hold temp when NOT in recirc, should also hold temp when it is in recirc mode. I doubt the water heater knows or cares where the water comes from.

 

[16ACE27]

I doubt the water heater knows or cares where the water comes from.

I agree

 

[Chateau_Nomad]

I self-installed my ShowerMiser. I installed a T in the PEX just before the pump (suction side). Note that my ShowerMiser only has two positions: To the showerhead or recirculate.

With it plumbed this way I got a lot of gurgling in the plumbing during recirculation, like air was entering the line somewhere??

That was short lived! I switched it to diverting directly back to the freshwater tank. I installed a valve at the original T and now use that for winterizing.

I think your issue may be coming from recirculating that 103° water back through the heater. Depending on how quick the thermostat reads the temperature and shuts off the burner may cause overheating?

If you were dumping the recirculated water back into the freshwater tank, your feeding the water heater essentially cold water. So unless you recirculated a LOT of hot water... like 8 - 10 gallons - I can't imagine the temperature of the freshwater tank would increase that much... unless your freshwater tank was nearly empty??

I measured my shower a couple times... a "Navy shower", and I used about 4.5 gallons. That's a pretty conservative shower. When I turn the ShowerMiser to recirculate it takes no more than 15 seconds to normalize the temperature... and that's NOT much hot water going back into the freshwater tank.

Honestly it wasn't that hard to plumb the recirculation line to the freshwater tank. Yes it means drilling a hole in the top, but with careful planning it's no biggie. Doing that resolved my problems... I think that's really the way the system is designed to function.

 

[Weissj62]

All I know for sure is this did not happen last year. I just have to figure out what happened that can cause this before one of my grandkids get burned with the hot hot water.

 

[16ACE27]

All I know for sure is this did not happen last year. I just have to figure out what happened that can cause this before one of my grandkids get burned with the hot hot water.

Take it to the dealer or call a mobile RV tech who is familiar with your tankless water heater.

Just another issue we never had with tanked water heaters.

 

[Weissj62]

That's probably what I will end up doing.
I'm starting to think the tankless water heater is not matching up to all the hype thay say about them..
If they do find something, I will update this thread.

 

[16ACE27]

That's probably what I will end up doing.
I'm starting to think the tankless water heater is not matching up to all the hype thay say about them..
If they do find something, I will update this thread.

The "hype" doesn't come from the users.

 

[Chateau_Nomad]

Call a tech... DO NOT let small children in that shower with that scalding danger! A qualified RV tech will know how to diagnose the problem. It might be an issue with the heater itself and nothing to do with plumbing.