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LindaH

Flushing Toilet Starts Water Heater

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We have a tankless water heater (Girard).  Lately we've noticed that when we flushed the toilet the propane burner on the water heater starts.  I never noticed until DH mentioned it today and he doesn't know whether it's been doing this since we left home on 11/4.

In October we had the RV into a dealer to have the DPH42 installed and to do annual servicing on the rig.  While it was in for service, the weather turned cold (in the teens at night), so we had them winterize the rig.

After we got the rig back, the weather warmed up, we dewinterized, loaded up the rig and headed south for the winter.  One thing we noticed right away was that when turning on the hot water faucet in the bathroom sink, the water that came out was foamy.  This lasted for awhile, but has since cleared up (we've winterized the rig ourselves and have never had this happen upon dewinterizing).

So we're now up to today when DH mentions to me that when the toilet is flushed, the water heater comes on.

Anyone have any ideas about what would be causing this?  Is there anything the dealership might have done in the process of winterizing that would cause this?

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Winterizing valve in the wrong position? I'm thinking the flow sensor, in the inlet of the heater, is seeing a small amount of water moving backwards inside the inlet piping, towards the lower pressure of the cold water lines.

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1 hour ago, Darryl&Rita said:

Winterizing valve in the wrong position? I'm thinking the flow sensor, in the inlet of the heater, is seeing a small amount of water moving backwards inside the inlet piping, towards the lower pressure of the cold water lines.

Sounds logical to me.

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7 hours ago, LindaH said:

On a tankless water heater???

 Atwood 50,000btu tankless water heater design. I never considered using one, for when you first turn on the hot water faucet the water will be cold at first, hot water to the faucet requires some length of piping from this unit. When you read the owners manual it has water temperature limitations.

Atwood On-Demand 50,000 BTU

Edited by Ray,IN
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5 hours ago, CFerguson said:

Could the hot water line be hooked to the toilet instead of the cold line?

We've had this rig for 7 years and this is a brand new development.  I know *we* didn't switch lines and I see no earthly reason why the RV service center we took it to would have done so.

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2 hours ago, Ray,IN said:

 Atwood 50,000btu tankless water heater design. I never considered using one, for when you first turn on the hot water faucet the water will be cold at first, hot water to the faucet requires some length of piping from this unit. When you read the owners manual it has water temperature limitations.

Atwood On-Demand 50,000 BTU

We don’t  have an Atwood.  Ours is a Girard, but I imagine they all work the same.

However, that doesn't explain why -- all of a sudden -- the burner on the water heater comes on when we flush the toilet.

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In thinking about your issues, it occurs to me that the flush valve does create a sudden surge of water and probably a sudden drop in water pressure with that. Might there be a check-valve in the water supply line to the tankless heater that used to prevent the water movement but has failed to allow it now? 

As I read this the water heater fires up but does not continue to run, and just shuts off again? If so it seems to indicate that something is causing a brief movement of the flow sensor to trigger it.

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27 minutes ago, LindaH said:

We've had this rig for 7 years and this is a brand new development.  I know *we* didn't switch lines and I see no earthly reason why the RV service center we took it to would have done so.

Yeah, it wouldnt be reasonable for someone to switch them, but if i read it correctly you did have someone working on a repair that involved hooking up water lines. Just trying to think outside the box until you can get it fixed. Best of Luck.

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3 hours ago, CFerguson said:

if i read it correctly you did have someone working on a repair that involved hooking up water lines.

Are you referring to this? 

On 11/21/2020 at 8:16 PM, LindaH said:

In October we had the RV into a dealer to have the DPH42 installed

What water lines would you need for it?

shopping?q=tbn:ANd9GcTy5_vLCA3Wypr6xfNYm

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As others have noted there is probably a drop in pressure when you flush.  

How is your water pressure?  City water or pump from tank?   If it is lower than you usually have the flow sensor on the input to the water heater may be more sensitive to the toilet flush.

One thing you didn't mention.... how long does the heater stay on when flushing?  The entire time flush water is running or just when first starting?

Do you have an outside shower?  If so, make sure both hot and cold are turned OFF - not just the plunger on the wand.  When those are left open they act as a mixer valve for hot and cold water and could easily result in your flushing with both hot and cold water.

Lenp

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4 hours ago, CFerguson said:

Yeah, it wouldnt be reasonable for someone to switch them, but if i read it correctly you did have someone working on a repair that involved hooking up water lines. Just trying to think outside the box until you can get it fixed. Best of Luck.

No, nothing was done to the water lines other than winterizing.  The only reason we had them do the winterizing instead of us doing it was because the RV was at the service center already, would be there for the next few days and the weather was going to get down to subfreezing temperatures.

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20 minutes ago, lenp said:

How is your water pressure?  City water or pump from tank?   If it is lower than you usually have the flow sensor on the input to the water heater may be more sensitive to the toilet flush.

One thing you didn't mention.... how long does the heater stay on when flushing?  The entire time flush water is running or just when first starting?

Do you have an outside shower?  If so, make sure both hot and cold are turned OFF - not just the plunger on the wand.  When those are left open they act as a mixer valve for hot and cold water and could easily result in your flushing with both hot and cold water.

Water pressure at all faucets is good.

We always run off the water pump from the tank even when we're in an RV park, which is rare.

The heater stays on the entire time...we can hear it running for awhile afterward, just like it does when using hot water at a faucet.

Both hot and cold are turned off at the outside shower.

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4 hours ago, Kirk W said:

In thinking about your issues, it occurs to me that the flush valve does create a sudden surge of water and probably a sudden drop in water pressure with that. Might there be a check-valve in the water supply line to the tankless heater that used to prevent the water movement but has failed to allow it now? 

I really have no idea whether or not there's a check valve.  We'll have to pull out the manual tomorrow and take a look.

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8 hours ago, LindaH said:

The heater stays on the entire time...we can hear it running for awhile afterward, just like it does when using hot water at a faucet.

You mean the water heater fires up for the duration of the flush, or until the flush is completed and the bowl filled? Stops when you release the flush valve handle/pedal? That seems a bit long for a check valve problem so it does now make me wonder if it could be related to something done when the dealer winterized it. Are we to assume that everything else is the same as before and all hot water is as hot and arrives in about the same time as before? Nothing at all is even the slightest bit different in terms of water use? 

In winterizing, is anything specific done to the water heater? I am not familiar with winterizing a tankless so am not sure what, if anything is done with it. It does seem very strange that this is happening right after it was winterized by your dealer. 

Edited by Kirk W

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1 hour ago, Kirk W said:

You mean the water heater fires up for the duration of the flush, or until the flush is completed and the bowl filled? Stops when you release the flush valve handle/pedal?

Right.  Except we can hear the burner continue for a short while afterward -- just like we can whenever we use hot water from any of the faucets.

 

1 hour ago, Kirk W said:

Are we to assume that everything else is the same as before and all hot water is as hot and arrives in about the same time as before? Nothing at all is even the slightest bit different in terms of water use? 

Yes, everything else is the same at all the faucets and the shower.

 

1 hour ago, Kirk W said:

In winterizing, is anything specific done to the water heater? I am not familiar with winterizing a tankless so am not sure what, if anything is done with it. It does seem very strange that this is happening right after it was winterized by your dealer. 

Well, when *we* winterized it (we've only done so one time), I ran the RV antifreeze through all the faucets, including the hot water faucets and shower head (without the propane on to the water heater, of course), including the outside shower and the toilet.  What the *dealer* did, I have no idea.  But, as I mentioned above, when *we* winterized the rig and then dewinterized it, we never had any foaming at any of the faucets.  *This* time after dewinterizing, the bathroom sink hot water continued to foam for a week or so afterward until it finally cleared up (although it still occasionally does so when we first turn on the bathroom sink hot water, but immediately clears up again).

It's a puzzler, for sure.  It doesn't hurt anything as far as I can tell, but it's certainly not normal and I'd like to get to the bottom of it.  

Edited by LindaH

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Linda, have your tried flushing for a period of time and then checking the temperature of the water at the toilet?  That would tell you very quickly if somehow the lines have been switched.  

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My thought process was that you lost physical control of your RV to the dealership for a short period of time so who knows what may have happened.  Could have even been a disgruntled employee, tho thats certainly a Reach!

I like Barbaraok's idea of tracing the flow of the hot water.

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5 hours ago, Barbaraok said:

Linda, have your tried flushing for a period of time and then checking the temperature of the water at the toilet?  That would tell you very quickly if somehow the lines have been switched.  

No, I haven't.  We're boondocking, so don't really want to waste the water plus I'm reluctant to put my hand in the toilet to check the temperature of the water (yes, I know it would be clean water, but still....). 😁

I can't imagine why the service center would have switched the hot and cold lines, anyway.  The only thing they did that had anything at all to do with the water lines was winterize and that doesn't involve disconnecting any water lines anywhere in the rig.

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2 hours ago, LindaH said:

I can't imagine why the service center would have switched the hot and cold lines, anyway. 

I think that at some point I would do as Barb suggests.I too doubt that they did anything like that but some water heaters have a mixing valve on the outlet to mix cold water to keep the temperatures down a bit, at least on some tank type water heaters. I don't have any idea if your system would have something like that which could possibly cause it to draw hot water, but clearly something is affecting the water flow sensing device to make it fire up. Another test that I would run to to open the cold faucet all of the way to see if that triggers it. 

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1 hour ago, Kirk W said:

...some water heaters have a mixing valve on the outlet to mix cold water to keep the temperatures down a bit, at least on some tank type water heaters.

That's not the way this water heater is set up.  There's a temperature dial in the bathroom where you can increase or decrease the temperature.  We set it so that we can take a shower without turning on the cold water.

 

1 hour ago, Kirk W said:

Another test that I would run to to open the cold faucet all of the way to see if that triggers it. 

Yes, it does.  I'd never noticed it before since I almost never turn on the cold water.

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