Tankless Water Heater Issue

[Grant]

Hello, I am new to RVFORUMS and need some assistance. I replaced my Surban/Dometic 6 gallon water heater in my 2016 Newmar Bay Star Sport. I installed a Fogatti Tankless Water Heater. All the connections went well however can't get the unit to ignite. Spoke with Fogatti Service Tech who walked me thru trouble shooting to no avail. At his instruction he had me close the values and disconnect the hot water hose from the plumbing to let water run into a bucket, then turn the values back on to the proper position. At that time the unit blower came on and the ignited and we had instant hot water coming out of the unit into the bucket. At his direction I reconnected the the hot water hose but nothing happen. I still had cold water but no hot. The only difference was reconnecting the hot water hose. I know the unit must have water pass thru the lines to activate the impeller which causes the Tankless Water Heater too ignite. I don't understand the logic in moving the hot water hose over several inches and reconnecting it to the hot outputted why this should cause this problem. We bled air the air out of the water system and repositioned the Hot/Cold/Bypass Valves which made no since. Requesting if anyone has any knowledge of what maybe the issue. Thanking all in advance for you support and comments.

 

[tdkkart]

The service tech had you disconnect the hot side of the heater and run it into a bucket, what this did was remove any restriction at the output of the heater, and proved that the control in the heater worked when there was enough flow. So you've proven that the heater will work.
Then, when you reconnected the hot water line to the coach, the heater won't come on, correct?
If this the case, it sounds like there is enough restriction somewhere in your coach's hot water plumbing that you cannot flow enough water through the heater to make satisfy the igniter circuit.
Have you tried turning on all the hot water faucets to increase the flow??

 

[Grant]

Yes Sir, we did that repeatedly with no joy. However I would assume that when the cold water was on and running, the cold water would activate the igniter going into the unit, not coming out of the hot water discharge.

 

[tdkkart]

I don't have any direct experience with these units in RVs, however in most cases, including the one that I have at home, there is a small impeller in the pipe inside the heater that measures the flow of the incoming cold water, the same water that comes out the other side as hot water. There has to be enough water volume going in and coming out to spin the impeller to tell the unit to ignite.
RV plumbing systems have a myriad of valves, elbows, t's, faucets, pumps, filters etc between where the water comes in and where it comes out of the faucets. Apparently your cold side will flow enough water INTO the heater, and hot water OUT into a bucket, you just need to figure out what is restricting the hot water output after you connect it back to the coach.

 

[tdkkart]

OK, according to some Fogetti documentation I found, it appears that the unit requires a minimum of 1 gallon per minute of flow out of the hot water line to operate correctly. So, go to your shower, unscrew the head and stick a milk jug under the pipe and see how long it takes to fill it. If it takes more than 1 minute, the heater will never ignite.

 

[Grant]

I don't have any direct experience with these units in RVs, however in most cases, including the one that I have at home, there is a small impeller in the pipe inside the heater that measures the flow of the incoming cold water, the same water that comes out the other side as hot water. There has to be enough water volume going in and coming out to spin the impeller to tell the unit to ignite.
RV plumbing systems have a myriad of valves, elbows, t's, faucets, pumps, filters etc between where the water comes in and where it comes out of the faucets. Apparently your cold side will flow enough water INTO the heater, and hot water OUT into a bucket, you just need to figure out what is restricting the hot water output after you connect it back to the coach.

OK, according to some Fogetti documentation I found, it appears that the unit requires a minimum of 1 gallon per minute of flow out of the hot water line to operate correctly. So, go to your shower, unscrew the head and stick a milk jug under the pipe and see how long it takes to fill it. If it takes more than 1 minute, the heater will never ignite.

At the Service Techs request, I took photos of my facets running water which I forwarded to him. According to the photos and after his review he said that was clearly enough water running through the pipes and was more than 1 gallon per minute.

 

[osuallen]

Are you not getting water flow from the faucets in the hot position, or water flow that never gets hot? if the former, you have a valve or restriction somewhere. If the latter, try the test suggested by tdkkart. if there are no restrictions, you will typically have much more than 1 gpm flow at that point. However, quite possible to have <1 gpm at a lavatory faucet set to a blend of hot and cold.

 

[tdkkart]

At the Service Techs request, I took photos of my facets running water which I forwarded to him. According to the photos and after his review he said that was clearly enough water running through the pipes and was more than 1 gallon per minute.

OK, Im impressed that a service tech can tell the difference in maybe a 1/4 of a gallon a minute from a photo.

 

[Kevin D Pem]

I once had a instant hot water heater that required 0.5 gallon flow.

A water conservation shower head kept it from working. Honestly it was much harder to have a good shower.

 

[Kevin D Pem]

OhhKAAAY!
My response was not helpful! (yes talking to myself again). I did keep using the tankless system, but changed my plumbing somewhat.

You see, My trailer was a 1973 Silverliner(last year made) so the fresh water tank was 15 gallons. That experience has kept me aware of water usage! It also taught me that mods are always a good thing.
What I did was add a 2 gallon insulated tank between the heater and the hot water demand. I also added a return valve at the different taps.
When I needed hot water I opened the valve and allowed the water to return to the holding tank to save water. This also limited how long I could shower thus saving water.

I still have a tankless water heater that is "portable?" I guess? I use it for outside showers, this outside shower saves water!

Still doing the conservation thing!