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 Thermostat preventing instant hot water on Noritz tankless?
Author: Dgainey (CA)

We have a Noritz tankless water heater for which our recicrulating pump recently went out. We contacted our local plumber who installed a Grundfos UPS15- 55SFC pump along with the Grundfos Timer and Clip on thermostat control. The recirc pump is set to run the majority of the day and night. It turns off at 11PM and turns on at 4AM. The temperature is set to 130 degrees.

I understand that this is a non-adjustable thermostat. We live in Southern California, Simi Valley and it gets very hot here in the summer.

Our tankless and recirc system are located in the garage.

The problem we are experiencing is that we no longer have hot water on demand, when it is hot outside. I know this may sound odd but when taking a shower or running the kitchen faucet water in the summer, the water initially comes out warm, and then becomes cooler and cooler, then after about one minute of running the water it finally starts to get hot.

Our pump was installed in early September when it was very hot. We reported the problem to our plumber. He came and made some adjustments. It has been cold since his adjustments and we thought the pump was now working unfortunately this does not seem to be the case. We just had some very warm days and again experienced the lack of immediate hot water. We contacted the plumber and he is going to order a new pump. Thing is we believe that perhaps the pump is not the problem.

I found the following regarding the thremostat:

The timer only allows the pump to turn on at certain times. So if you only need hot water in the morning, you could set the timer for 6am to 8am. Then the pump would only recirculate the hot water during that time. The thermostat turns off the pump when the water in the pipes reaches a certain temperature. So once the water in the pipe is hot, the pump turns off. When the timer and thermostatic controls are installed together, in series, the circulator operates ONLY at the preset clock times specified by the user AND ONLY when the temperature conditions of the thermostat are met. That is, if either the timer control or the thermostatic control switch is open (off), the circulator will not operate.

In addition I see that the settings for the thermostat are:

The thermostatic control automatically turns the circulator off when the temperature in the hot water line exceeds approximately 105°F (as in the case of periods of no demand) and back on when the temperature falls below approximately 85°F (as in the case of periods with high demand). Temperature accuracy of these thermostats is not "perfect" within 1/2 degree. If you must have a "perfect" accuracy thermostat, then these are not for you. These thermostats are great for the right application, which is to turn off when the "approximate" temperatures have been reached, and turn on when the "approximate" temperature has declined down to approximately 85°F.

Had we not had a very efficient system for three years, providing us with instant hot water, we might not have noticed the performance difference.

Please advise as to how we can return our system to its previous state of providing instant hot water regardless of the temperature outside.

Thanks in advance,
Debbie

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: packy (MA)

i don't understand?
it your pump failed, why did someone change to a different pump and wiring configuration?
use the same (or similar) pump and the existing wiring set-up...

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: Dgainey (CA)

Plumber said the pump we had was not a very good brand. It was an Armstrong Astro 25 BS. He recommend the Grundfos as a replacement. Said we should have a thermostat also.

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: LemonPlumber (FL)

Please relocate the thermal cut off/aqua stat to the coolest fixture room inside the house at the circ loop return..Low voltage wire is easily moved and the current location of the clic switch seems to be effected by outside temp. This should resolve the issue as said.I would change you over to a Metlund on demand circ motion controlled system and leave the timers and clic sensors out.Each fixture would call for hot delivery as you neared it and is perfect fit for tank-less.In some cases more than one unit could be installed where less used fixture demand would not need the instant hot .Ask your plumber to relocate the thermal high limit for now with the pump you have and then when you need to change, go upgraded.I love Grundfos pumps.And less than Metlund pumps are.But the use is better controlled by Metlund.I am looking forward to an advanced Grundfos tank-less circ/comfort system!!

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: Dgainey (CA)

Thank you. This makes great sense. It seems we have a good pump, but the comfort system is not yet perfected.

The problem is only a small portion of the return line is in the garage. The rest of it is in the attic which would probably be hotter than the garage in the summer. What do you suggest? Disconnect the thermostat?

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: LemonPlumber (FL)

I would prefer relocate.It stops the water temp from being wasted.Btu lose from circ lines can be large.Where the return line is heated it is ok.but install the thermal clic/aqua stat to the cold return segment of the line.May be just before where it jumps up into the high temp area.It still works out to reheat less water than reheat it all.Honestly yes .You could just remove the use of the thermal clic/aqua stat until temps drop.Please see how far apart you can use the Grundfos timer pins for best energy savings.Most of my customers have insulated lines and one pin on the hour leaves the timer working no matter how short it falls from true time of day.Two hours of btu lose is nothing when a guest loves hot at three in the morning.

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: SMSPlumbing (PA)

The old circulator ran on a timer only. That is why you always had the hot water when needed. The new one has the thermostat which senses when the water gets warm and then shuts it off. If the return line is getting heated in the attic, it may be exceeding the temp for the circulator to shut off. Doing away with the thermostat and running on time only, should get you squared away. The Grundfos is a nice pump, but the current set up is causing you your headaches.

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: Dgainey (CA)

Thanks for your response. We can do this but do you think it is a problem to run the pump for longer periods of time?

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: Dgainey (CA)

Thanks for all your recommendations. We will probably go with your hourly pin solution as we believe the location of the cold water return segment is at the furthest end of our house and not easily accessible. do you think running the pump at longer periods of time is a problem for the Grundfos? Thank you again :)

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: LemonPlumber (FL)

It does increase your cost.You need to see it .As it does not have too.The idea is perfect.it takes work to make perfect work.So use the timer and try to use less to save more.You decide where the cost lets you pay a little more to play!

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: steve_g (CA)

IMHO, Grundfos makes a good pump and it should have no trouble running 24/7.

Also note that Noritz recommends that a small 8 ~ 10 gallon tank is installed inline with a recirculation loop (to avoid 'cold water sandwich'). This can be a small electric water heater which does not have to be plugged in.

You can download piping diagrams here:

[www.noritz.com]



Edited 2 times.

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: hj (AZ)

IT is too tedious to try to dig through your "diagosis", but the crux of the matter is that the heater SHOULD turn on when water flows through it, regardless of whether the flow is caused by the circulation pump,(and some pumps do not generate enough velocity to turn tankless heaters on, but that is a different problem than you have), or your opening a faucet. IF that does not happen, then either the water is NOT flowing through the heater or the flow switch is defective. One thing that could prevent, or limit, water flow through the heater is a defective, or missing, check valve in the circulation line which would give the cold water a more direct path to your shower valve. This would cause either NO hot water, or erratic temperatures at the shower.

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 Re: Thermostat preventing instant hot water on Noritz tankless?
Author: Scott D. Plumber (VA)

Depending on the Nortiz you have and the flow losses in your plumbing system, the pump may be too small to do the job. I would not put anything smaller than a Taco 009 on a recirc and prefer the Metlund D'mand option much more. If I were you I would look inot that since you already know that the pump you have will not work. I looked at the curve on this pump. At 16'hd (Average loss through most tankless units) you only show about 2gpm on the curve and that's before piping losses. You get much below .6GPM and the heater won't fire. If it is a condensing modle the Head pressure is even higher.

Look at the Metlund S-70 D'mand Pump

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