I recently had a natural gas exterior rinnai tankless water heater installed. The old system was a standard electric tank system with a re-circulation pump. When they installed the new system the plumber removed the old re-circulation pump and sealed the line coming in to it and out of it. Now with the tankless installed, every time water is used (hot or cold) a pipe knocks (this knock is harder and different than a normal hot water expansion knock and sounds like the pipes are banging against something inside the wall. Could this be happening because of the way he cut out the re-circulation pump and didn't replace the pump with pipes to maintain the loop system. The tankless system does not have a re-circulation system capability.
Also should the heater be mounted flush up against the outside wall? I noticed on the internet that some tankless systems have mounting brackets but the actual tank is about an inch off the wall. When the heater turns on, it is noisy inside the house.
Lastly, the plumber tapped into a hot water line near the heater but did not run any lines directly to any outlets. I have a low water eco-friendly washing machine and I doubt that any hot water gets to the washer because of the low water usage. The tank is 47 feet from the washing machine and 40 feet from the kitchen sink and dishwasher which takes 30 seconds for hot water. Is there anything that can be done to help get hot water to that side of the house? Help I am frustrated.

the time to have addressed these issues was before the change-over was started..
so, go to rinnai's web site, look up your model and install a recirculating line according to their instructions.
probably have to put a small electric tank and recirculate to it..


[www.rinnai.us]



Edited 1 times.

Having a tankless water heater doesn't make the hot water get to far away sinks and other fixtures any faster. The length of the hot water pipe from whatever is heating the water (tankless or traditional tank heater) is what causes the delay for hot water to come out of the faucet. That was what your recirculation pump was for, to keep hot water present at the fixtures far away from the water heater.

The advantage of a tankless heater is that once hot water reaches the faucet it will be endless. And the tankless should use less energy (elec or gas) because it isn't keeping the water hot all the time, only heats as you use it. However, for some people the energy savings doesn't happen so much because with endless hot water they can take longer showers.

If you draw water thru the tankless too quickly it can not heat the water as hot as you want. For example, if you are showering and someone in the kitchen starts the dishwasher or is using hot water some other way the water flow thru the tankless can be so large that the tankless can't heat it as high as you want, and the temp of the hot water will drop. So the tankless heater has to be matched to what you connect it to. A large whole-house tankless heater will be able to heat several gallons per minute, a smaller tankless may only heat 1 or 2 gallons per minute.

Another pitfall with tankless heaters is that you have to have a minimum amount of water flowing thru them for the tankless heater to switch on. But normally this doesn't have to be a large flow, something like .2 to .5 gallon per minute. So I'd think your washing machine should work ok.

Did the installer of your tankless heater select it for you, or did you pick it out? Also, did he check things afterwards to see how well the hot water got to various places like kitchen sink, shower, laundry?

The banging pipe may be water hammer as the water is quickly shut on and off, or it may be a pipe that is moving against another pipe or other solid object and making the noise. If this pipe noise wasn't happening before the tankless was installed then I'd look at the recent piping changes to see if they are where the noise is. I'd also consider mounting the tankless heater as you said so that it isn't directly touching the wall. Some installations mount the tankless to a thick board and the board is fastened to the wall to reduce noise conduction. On some tankless heaters the mounting brackets extend to the rear so that the back of the tankless heater does not touch the wall, there is an air gap back there.

Sometimes people are disappointed after getting a tankless heater. They have some disadvantages that can be made worse by improper installation. If your old tank-style water heater is still working ok and sitting there it can be reconnected.



Edited 8 times.

Thank you for your quick response. I had the new heater installed through the electric and gas company and they didn't support one with a re-circulation system. I have recently learned that a re-circulation pump can be installed without voiding the warranty. The plumber who installed the system called me today and he is stopping by to check out that alternative. Thank you again, your information was valuable.

Thank you for the help.

The electric and gas company had the heater installed. We agreed last week for them to remove it, refund my money and pay for installation of another kind of water heater. I was researching alternatives but arrived at the same conclusion I did before and that was that I wanted a tankless unit. The plumber hired by the gas company called today. He contacted Rinnai and they have a way of installing a re-circulation system without voiding the warranty. He is stopping by this afternoon and is going to spend some time investigating the banging sound.

Your information was very helpful because I was able to talk with the plumber on the phone and actually sound like I knew something about this. In any case, maybe we can salvage the system and all go home happy.

I very much appreciate your kindness and time in answering my questions.



Edited 1 times.