Lukewarm/fluctuating Hot Water with Recirculation Pump
We've had fluctuating hot water on all showers/faucets since we moved into this house with the builder installed recirculation pump. We noticed the problem when we first moved and, while under warranty, the builder sent a plumber who said the pump's cartridge was getting stuck. He replaced the whole pump since he didn't have the cartridge on hand. It seemed to work well for about a year since we noticed no fluctuations.
Now it started doing the same thing and I personally replaced the cartridge with an OEM one but the problem is the same: fluctuating water temps.
I am wondering if the setup done by the builder is correct. Is the pump installed in the right direction?
If so, what else could it be?
Pump:
Taco 008-IQSF6-IFC
Comments
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Hmm…where to begin?
If this problem is as you say and not changing when thoughts in service are applied. I would suggest not using the recirc. Bypass the thing and see if that helps. Why is there recirc in the first place? Is it really necessary?
After bypassing look at the fixtures. Check to see if the problem goes away. If the problem does go away in some but not all of the fixtures you can troubleshoot that.
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You have our "Smart Pump". Do you know what mode you are in, Smart or Pulse?
If the Mode LED is solid, you are in Smart Mode. It will learn your usage for the week and bring on the pump the following week during those times. It will learn week to week, so if you change your habit, then you might want to be in Pulse Mode.
If flashing, you are in Pulse Mode. You have the option to have the pump run 1-10 minutes ( factory set to 3 minutes ) and then off for 10 minutes.
The arrow on the casing if pointing down, so that is your direction of flow.
Please give Taco Technical Services a call during normal business hours Mon-Fri 8am-5pm EST 401-942-8000 and just ask for Technical Services.
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I have it on Pulse mode. Do you know the purpose of the external sensor? What does it do?
Has the pump been reliable for you? I wonder if maybe mine is defective.
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Thanks for the suggestion, it should help isolate the problem. I know nothing about plumbing, so how can I bypass the pump?
I do need the pump because without it hot water takes 3+ minutes to reach some places.
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I also have noticed that if the pump comes on when I am taking a shower then the water gets hot as normal, but as soon as it shuts off, it gets lukewarm again. (The pump runs for 3 minutes every 10 minutes)
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The external sensor needs to be wired to the controller in order for the pump to work.
In the Smart Mode, the sensor will sense a rise in temp and record it for the following week.
As long as the pump was properly sized and installed correctly, it should last awhile. Unfortunately, hard to put a time table because it depends on to many variables.
Was the system purged of air? Can you take an amp reading off the motor. The 008 should draw 0.84 amps under normal conditions.
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Not sure if it was purged. What's the best way to do it?
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It looks like you have a hybrid water heater (heat pump design with back up electric elements).
This type of recirculation logic (continuous pulse) is usually not recommended by the manufacturers of hybrid style water heaters. These water heaters have such a long recovery time when running in heat pump mode that when the pumps run excessively, it cools down the water heater too quickly.
The job of a recirculation system circulator is to not pump a ton of hot water around the house, it just needs a trickle to keep the pipes "primed". It sounds like your pump is working fine.
With hybrid water heaters, it is suggested to use an "on-demand" type of recirculation logic. Smart pulse as @SteveSan was suggesting is better with what you already have while the Genie is better for the operation and recovery of your water heater.
Dave Holdorf
Technical Training Manager - East
Taco Comfort Solutions
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Thanks for the suggestion. Yes, it's a hybrid water heater. The builder's plumber installed the pump on Pulse so that supposedly we would have hot water almost instantly. I will change it to Smart mode and see if it makes a difference.
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When changing it to pulse, it is going to take 7 days to learn your patterns. For these next 7 days, it will still operate in the pulse mode until it learns so you will not notice anything different right away.
What brand water heater do you have? I would like to look into the information as to their recommendations.
Dave Holdorf
Technical Training Manager - East
Taco Comfort Solutions
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AO Smith
Model HPTU-50N 130
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Page 13 of the installation guide with this model does not recommend a recirc loop in order to maximize the economy of operation. However, these instructions were written in 2015 and maybe they have done other research and testing with their units and have recommendations.
Also on this page, which may help more with your water temperature fluctuations is maybe adding a Thermostatic mixing valve as they show in the middle of the instructions.
Dave Holdorf
Technical Training Manager - East
Taco Comfort Solutions
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Thanks again. Well, this might be the issue. Maybe the recirculation pump is not intended for this water heater. Will change to smart mode and report back in a week
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When changing it to pulse, it is going to take 7 days to learn your patterns. For these next 7 days, it will still operate in the pulse mode until it learns so you will not notice any difference for at least a week, so you may need two weeks before the change
Dave Holdorf
Technical Training Manager - East
Taco Comfort Solutions
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I have no idea as to how the pump you have operates since I have never seen that pump but let me ask the others if there should be a check valve in the recirc line to prevent cold water from backing up the recirc line.
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Hi, I do not see a check valve in the recirc line. Is there one in the pump? If not, you probably are getting flow backwards through the reirc line when water is used, which will give temperature fluctuations.
Yours, Larry
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@Larry Weingarten and @retiredguy,
This model has the check valve installed internally at the discharge flange the part number "Taco 008-IQSF6-IFC" has IFC at the end denoting the Integral Flow Check is installed in the circulator when shipped from the factory.
Yes, I have had that happen at times as well 😎
Dave Holdorf
Technical Training Manager - East
Taco Comfort Solutions
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Is all the hot water and return piping insulated?
The gpm that the pump needs to move is dependent on the heat loss in the loop. Sizing info in this issue of idronics
That is what the sensor on the return is looking at, assuring the entire loop dropped about 10 degrees
Really it is the most remote fixture that you want hw delivered to, it can drop lower on the return after that, it just costs you more operating $$
If the loop is not insulated it may be better to start the pump only when you use hot water, a “demand” system.
A number of way to do that with door switches, proximity switched, etc
The sensors are usually a 105- 110 temperature, so the return needs to be that warm if the pump is sensor controlled, to shut the pump off.
If you have a 120V hp, you could have more loop loss than what the tank can keep up with?
What temperature is the tank set at?
Often times the HP are set to 140, and a mixing valve used. This gives you more draw down and better temperature stability. But the correct valve or a bypass needs to be piped with a thermostatic valve
A Caleffi 520 valve is a good option for HPWH, no bypass is needed
You need a check on incoming cold, and a thermal expansion tank, perhaps
https://idronics.caleffi.com/sites/default/files/magazine/file/idronics_33_na.pdf
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Is this pump "mounting specific"? By that I mean, that most pumps with a check valve in the discharge can not be mounted with the check valve pointing down which would allow the check to remain open all the time. I would check the mounting directions to see if the pump needs to be rotated so the water flow is up and not down as it is in your case. I also read somewhere that the check valve is an optional item. Your problem may be that the pump is mounted incorrectly and will have to re-piped to get the flow direction correct.
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After much tinkering around, I figured out that the problem is once again a faulty IFC. As explained in my first post, I had changed the IFC right before coming here. It seems that new replacement was also faulty- it was stuck open. I have once again changed it and it works good… for now. Seems to be a flaw of this pump. This is the 4th IFC in less than 3 years.
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what had it stuck open?. Dirt or scale? Perhaps a y strainer upstream would help.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Have you gotten this system to operate properly or is it still a problem?If itis still not working properly then I believe that the pump is mounted incorrectly as I wrote above.
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@hot_rod It looked to me like a very small piece of scale was keeping it open. Yet again, this is my 4th IFC. Seems like they're prone to getting stuck open.
@retiredguy Has been working good since September, but I am almost positive it will happen again. At least now I know for sure that the problem is the IFC. I even bought an extra one to have on hand.
Thanks again to all for the help.
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