Tankless water heater and Circulator pump

Im hoping someone can help. We just purchased a home with a tankless water heater (natural gas) and the water takes a long time to get hot. There is an Grundfos Alpha1 circulator pump that ties into the hot water line next to the water heater in the crawlspace but it isnt plugged in. Could this be the source of the problem? Our last home had a tankless hot water heater powered by natural gas but I wasnt aware that we had a circulator pump in that home. Anyone who could shed light on how this system is setup to operate would be greatly appreciated.

Many tankless water heaters have built in circulator pumps. What brand do you have.

jparker371 said:

Im hoping someone can help. We just purchased a home with a tankless water heater (natural gas) and the water takes a long time to get hot. There is an Grundfos Alpha1 circulator pump that ties into the hot water line next to the water heater in the crawlspace but it isnt plugged in. Could this be the source of the problem? Our last home had a tankless hot water heater powered by natural gas but I wasnt aware that we had a circulator pump in that home. Anyone who could shed light on how this system is setup to operate would be greatly appreciated.

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Are the faucets far from the water heater? Does that circulator pump make a loop? I've heard of people setting up a loop with a special valve or sensor so that the pipes can have hot water right near each faucet for quick hot water. I was actually thinking of doing something similar myself because my tankless hot water heater needs to make a trip of around 45 feet before it reaches my first faucet. Even with half inch lines it still takes a good while to get hot water there.

If your going to circulate then get rid of tankless. The heater is constantly running while circulating. So in stead of only hearing what you need at 180,000 btu. Your heating extra to be ready for you in a set time. Even putting in a holding tank rated for hot water. You will kick on 2-3 times a day.
So compare a tank style. Kicks on 2-3 times a day and only pulls 75,000 btu.
Best choice will be decided by your priority of time to get hot water to you vs how long you want that hot water serving you after it reaches you. Like my wife takes 60 minute showers twice a day. So we have a tankless. She turns hot on and sits to pee. Physically takes 85 seconds to reach our shower Then adjusts cold and she sitting pretty for as long as I can keep gas bill paid. Or like my mom who hates wasting the cold water to get hot. I got her set up on tank and circ pump. But most in the past that I set up like that have turned off pump and just wait for water because the gas bill sky rockets.
O and if pump is on timer then you forget to go reset time every electrical outage and your heating water at various parts of the day but when you need it.y company has learned to situate the heater about middle of the house.

I have an oil fires boiler with a tankless...no circulator.....I always got good hot water bu what I did was separated 1st fl and 2nd floor hot water feeds now I can isolate each floor separately

My tankless water heater is a Rinnai RUC 98.

mdk0420 said:

Are the faucets far from the water heater? Does that circulator pump make a loop? I've heard of people setting up a loop with a special valve or sensor so that the pipes can have hot water right near each faucet for quick hot water. I was actually thinking of doing something similar myself because my tankless hot water heater needs to make a trip of around 45 feet before it reaches my first faucet. Even with half inch lines it still takes a good while to get hot water there.

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the faucets arent far from the tankless unit. the unit is right under the master bath and it takes a solid minute for the water to heat up. additionally, the unit is set at 120F and the water doesnt even come close to reaching that temp, as you can stand under the shower head with it on full hot. thanks for all the help, what a great community to help us DIYers who need professional advice without the price tag. many many thanks in advance for all the help.

after doing some additional research I see that the RUC98 does have a built in circulator pump, why would there then be two installed in the water system of the house?

Check your gas supply. Must be 3/4” for maximum of 60’ then to 1”. Must be first in series on gas main if only 1”.

do you have it piped for recirculation?
Pics please.
You need a plumber who knows Rinnai and can check it out.
Rinnai tech service is only ok. That is why we only install Navien.

I recently did some research on tankless heaters. The conclusions I've come too are they are good at saving space and eliminating the problem of running out of hot water (if you have that problem, which I don't). On the negative side, they don't save you money because the maintenance cost is greater than the energy cost of keeping the water in a good tank hot. Also some people think it will give them instant hot water, but that would require a circulation setup that uses a timer that would only keep the water in the pipes hot at specific times. I think if you want "instant" hot water, the way to go is to install a point of use heater.

It may need to be flushed. Many times people do not know this. There is no tank for the sediment to settle. If the former homeowners were not aware or just didn;t do it, you may need to get someone in to service it.

I was a bit surprised to learn that it's common to circulate hot water based on a timer. When I worked in the industrial/municipal area we always based the activation of the hot water circulation pump on a temperature sensor located in the return line. If one wanted they could add a timer to the circuit to deactivate it during sleeping hours, etc.

EDIT: This subject reminds me of my old plumbing engineering boss that used to say he was thinking of running the hot water line to his toilet. With the idea that the first thing you do when you get up and go in the bathroom, is use the toilet.
I don't think he ever followed through with that idea though.

so it looks like a 3/4 inch gas pipe into the system and it is the last unit on the system but only the oven, stovetop, and fireplace are gas in the house. here are some pictures of the system and what we are dealing with.

the pump is disconnected at this time.

Whoever did that install is a hack...

thats too funny! why do you say that? what has been done in error?

voletl said:

Whoever did that install is a hack...

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I am kinda of afraid to ask also. Hot on left cold on right. Not looped in Like a lazy install.crimp pex would be my only issue but not an official issue just this plumbers preference of pex. I use type a. But I can’t wait to hear this too. Lol.

In the mean time your set at 120. That’s not hot. I think dpn switch 6. Read instructions for maximum temp. Then turn it to 135. See what dishwasher recommends might be 140

I wouldn't set it any higher then 135. That's pretty hot lol. 140 is starting to get dangerous, very easy to scald yourself when you start getting into the 140's (I think it only takes a couple seconds at 140 vs a good half minute or longer while in the 130's). This job is a hack because how crappy it looks lol. Not really done in error. Do Tankless water heaters have circulators? I don't understand why they would need them unless they either have their own recirculation system or it's also acts for heating your home with a closed system separate from the DHW. I can't see the point of a circulator otherwise because it all operates by pressure... You open a valve and the pressure will push the water out.

That circulator there is definitely a recirculator pump. Notice how it comes from a hot water supply (Or at least it should since its red pex lol) and then connects back into the cold? That's so it can activate the boiler and start heating. Without flow the tankless hot water heaters don't do anything. I wanted to set mine up to a switch near the thermostat and attach a timer to it so it goes off every 15 minutes or so and do a recirculating system like that. Some people do motion detectors. Can you tell how your pump was hooked up?

I would think that boiler would have some sort of error message if its being deprived of gas. But 3/4" line all the way through running several components like that... definitely not good. You should be starting out around 1 1/4" or 1" and each appliance would be served by 3/4" or 1/2" depending how many BTU's it requires. You lose a lot of supply at each appliance if they are all being ran at the same size as the main. There's some charts you can look at online by googling them to figure out if your line can supply all those components at the same time.