Tankless Water Heater and P1 Error Code when using a Water Recirculation Pump
 

I recently moved to The Villages and my home has a Rheem tankless hot water heater. When running one bathroom faucet and the shower at the same time (with the little O-ring in the shower head removed) it takes 1 minute and 16 seconds to get hot water to the shower. Due to the length of time that it takes to get hot water to the master bath I installed a Watts premier water recirculation pump.

I previously installed the same pump on the water heater at my previous residence with no issues whatsoever. The only difference being that my previous residence had a standard type water heater as opposed to the tankless water heater used in my new home

After installing the pump and setting the timer, the hot water heater would not turn on and displayed a “P1“ error code, which indicates that there was not enough water flow being generated from the pump to the hot water heater in order to get it to turn on.

I’m reasonably certain that some other people have installed water recirculation pumps on tankless hot water heaters and was wondering if anyone else has experienced the same error code after doing so? What did you do to correct the situation?


UPDATED 5/1/24 @ 9:57 a.m.
I contacted Mike Scott Plumbing in Wildwood and inquired about having them install a water recirculation pump for a tankless water heater. They informed me that they only provide this service for the standard hot water tank installations - not tankless hot water heaters.

I next contacted RHEEM and described this issue I was experiencing. The support person I spoke with provided me with some documentation on a TACO recirculation unit, however, the installation process was quite a bit more detailed than the solution I initially installed. I inquired about other possible solutions from other manufacturers but the only one they could discuss with any certainty was TACO system.

I guess my updated question to the forum is this: Has anyone on this Forum who has a RHEEM tankless water heater installed a water recirculation pump? If so, what brand/model did you use?

Thank you.

UPDATE 5/2/24

After a lot of research I found a solution that works. Another call to Tech Support at RHEEM and I explained the complications involved in installing a dedicated return line and my preference to use a bridge valve. The person I spoke with told me that the specs on the RHEEM tankless heater model that I have requires a minimum of a 5 GPM flow rate and a 25 Head. She explained that as long as I had a way of turning the pump off when the water was heated, that any pump with those specs should work.

I found a pump on Amazon made by BACO Engineering (unfortunately made in China) that has a 20 head and up to 13 GPM flow rate. Since the terrain here is fairly flat and I have a one-story home my hope was that the 20 head would provide an adequate lift to maintain pressure throughout the system to the bridge valve. The pump is equipped with a flow meter that automatically turns off the pump once the water passing through the bridge valve reaches 95 degrees and causes the bridge valve to close.

There were a few minor issues experienced while installing the pump since the pump is chinese and the thread on the male end of the pump inlet didn't seal well on the NPT fitting, but that was resolved with a lot of teflon pipe tape.

The pump tested well and is now equipped with an Alexa plug that has a routine set to turn the pump on/off at designated times. The total cost of installation (Pump + Bridge Valve + CPVC and flex hose fittings was about $190. Some may argue that the juice isn't worth the squeeze, but for me it's more of an issue of saving water. After running the recirculation pump I get reasonably hot water within 10 seconds.

Thanks to those of you who offered advice.

I would check with REHEEM Customer support. The Watts pump is a low volume pump moving water slowly not pressurizing system.

Rheem warranties the original owner only it seems. In any case, the warranty would be limited as the demand is not both temperature and flow controlled.

How does the circulating water get back to the tankless system when the faucet is closed? I have a regular system and when the pump is running I have a valve that opens between the hot water line and the cold water line and the cold water line is used to returns the hot water to my hot water heater. Sounds like your system is not returning the water.

AI suggest the following. Choose the right recirculation pump for your tankless water heater model.
Install a check valve and sensor valve in the recirculation line.
Install an aquastat on the tankless unit and connect it to the recirculation pump.
Set the temperature on the aquastat to the desired level.
Turn on the pump and test the system to ensure it’s working.

It sounds like my system is using either the same, or a similar valve as the one you may have. The water recirculates internally using a diverter valve that is installed beneath a sink which ties the incoming hot water supply line to the cold water supply line and allows water in the hot water supply line to flow into the cold water supply line when the pump is active, thus acting the same as a dedicated return line. The diverter valve has a temperature controlled shut off or check valve inside it so that when the temperature of the water passing from the how water supply side of the valve exceeds a certain temperature, it will close.

I was able to test the valve by simply shutting off the incoming cold water supply at the diverter valve and then turning on the cold water at the faucet. Water flowed from the faucet indicating that water from the hot water side of the diverter valve was being supplied. As the water eventually heated, the water flow slowed and eventually stopped when it reached the prescribed temperature. For that reason I'm pretty sure that the valve is working properly.

From additional testing that I've done, it seems that (as suggested by another forum member) that the pump flow rate of the Watts system is not adequate enough to cause the hot water heater to turn on. As soon as I turn on the pump, the water heater throws a P1 code. If I leave the pump running with the P1 code still active and turn on the hot water inside the home, the P1 code instantly resets and the unit fires up.

At this point I believe that I will try to find another pump that has a higher flow rate. I looked for the GPM or flow rate specs online for the Watts pump but could not find any. There is another pump made by Grundfos that claims it can provide up to 9 GPM.

Thank you for your help and in pointing me in the right direction.

I believe you nailed it! Thanks. I believe I need a higher volume pump.

IMHO, I would also add a timer to turn on your system just before you typically take your shower, otherwise I am GUESSING you will be wasting a lot of energy. On a side note, I turn on the shower to full HOT, wait 30 seconds, move the shower handle to a known comfortable heat setting, and 4 seconds later shower is ready.

The standard tankless hot water heaters here are not rated for recirculating. This will void the warranty.

Also likely your gas bill will be noticably higher.

Look at your water bill. Yes, it takes some time for the hot water to reach the faucet. But is saving that volume of water going to make enough of a difference in your bill?

I had the P1 error code intermittently and it was due to a bad regulator from the water supply line to the Rheem (at the Rheem). I Paid $45 for the regulator, $75 for the service call and $25 for the 15 minutes it took to replace it. I use Mike Scott Plumbing. Hope that helps.

The tankless recirculating units are much bigger than the non-recirculating units. Maybe you have to change out the tankless unit also. Our recirculating pump at our last house was picky on how it all worked depending on the temp setting of the circulating pump. If you set it too high, the pump would never stop because it was trying to get to a temp that would never materialize from the heater. Too low, and it would not recirculate because it met the desired temp.

An easy free solution. Turn on all the sink hot faucets and the shower in the bathroom. In 30 Sec you get hot water. Turn off the sinks and step in the shower. The tankless systems have a low and a high demand heat setting. With only the shower running it will be in low demand and take about 2 minutes to get hot water. With the sinks on, it will be in high demand. With flow restrictors, its probably a gallon of water in either case.

Some people remove the flow restrictors which has the same effect as shifting the heater into high demand from what I hear.

Yeah it's an adjustment. I turn on the hot faucet and do other stuff first, like brush teeth in the bathroom, or set up in the kitchen.

You are dealing with a small quantity of water from the water heater to your shower faucet. In 50 feet of three-quarter Inch CPVC pipe there is only one and 1/3 gallons of water.

Correct, I've measured it takes about a half gallon here.

There is a temperature drop of 5-10 degrees so the efficiency recirculating would not be very good.

That is almost exactly what I did.

First , I removed the water restrictor in the shower head .

Then , I turn the hot water to full hot and full volume at the shower head while at the same time , I have the hot water running on ONE of the bath sinks .

In 35~40 seconds, I have piping hot water flowing.

Turn off the sink faucet and then adjust the temp at the shower and turn down the pressure at the shower valve .

Because I removed the restrictor, that last step is necessary because otherwise, the volume of water coming out is too much !

All of this is at our master bathroom, the furthest point from the heater .

Is this the only way you can get hot water quicker, I live in Argyle, TX & have a Rheem Tankless water heater & I must run the hot water for 2 or 3 mins. before I get hot water. Is this a solution to get hot quicker that I have to spend more money to have a gizmo put on to get hot water. If I buy another home I guarantee you it won’t have any kind of Tankless Water Heater, besides the home I have now the Tankless water heater is outside the house. Just saying this is stupid. What do you think?

You may have installed the pump incorrectly. The pump shouldn't push water into the tank, the tank should push the water through the pump. I have a pump on a normal tank and unplugged it because it was too costly!

Whatever happened to the good old days. Our first home my uncle a plumber assembled a kit for me. Assorted washers, O rings, packing string and replacement seats. Single box and I had it all. Today, you need to have the proper ballcock to work with your water saver toilet. Only good news is flexible couplings. If, I could only find em I still have the tubing benders you needed and the special wrenches for compression fittings. Far as hot water, the OLD SOLUTION was to insulate the pipes. Our Villages home the master bath is very close to the hot water heater. Our single lever kitchen faucet. Too often we run hot when it should be cold.
You not only pay to heat the water but you pay to run your air conditioner to cool the hotwater in the lines.

There problem is the long water lines, not the water heater.

It takes time to push the cold water out before hot water makes the +50ft journey.

When we had our house built we had them install a recirculating water heater. They also installed a return line from our farthest faucet. I’m not sure installing a recirculating unit without a return line would do much good. Maybe they could run a return back through the attic?

Did you read any of the previous posts ? Including the one (mine) posted just above yours ?

I get hot water to the furthest point in my house in 35 ~ 40 SECONDS !

No gizmos or gadgets involved ….

Thank you for the suggestion, but the pump was installed on the hot water outlet side of the tank as required by the manufacturer and was set in the proper flow direction.

The pump that I installed was a WATTS Premier recirculation pump. I had installed this same model pump in my previous residence on a standard hot water tank with no issues. On the tankless water heater that I have here, the pump does not pump at sufficient volume to activate the hot water heater. The heater evidently requires a certain flow rate in order to turn on the burner(s) and the Watts pump did not pump in the required volume.

I removed the pump and I am back to square one. What I need is a pump that is manufactured to work with a RHEEM Tankless Heater.

RHEEM Tech Support recommended a TACO model: (Kit: AP18403) but that requires a dedicated return line. I'm sure I could probably crawl through the attic and get the piping to install one, but my preferred solution would be to use a pump that incorporates the use of a bridge valve.

Rheem is Right! Recycle System Requires a Return Line For Tankless Hot Water System
 

Based on many years of designing and troubleshooting complex water distribution systems Rheem is correct. A tankless system requires a dedicated return line. The conventional water heater and tank system works with the Watts system because the tank provides a buffer for both water supply and water temperature control. Cold water enters based on supply line pressure and balanced by the expansion tank bladder. If pressure exceeds the pressure relieving set point the water comes out into wherever the drain line directs it.

The tank heaters turn on and off according to their set points. Temperature change is gradual since the tank inventory slows down temperature change.

The Watts recirculating pump is a low flow rate, low pressure increase pump. The pump only has to provide a small amount of pressure increase to overcome a small amount of piping pressure drop. So it works with a tanked system.

The problem with a tankless system is that it has no storage buffer without a dedicated return line to be able to control the tankless heater within its setpoints. If you have a dedicated return line, initial flow is the inventory of water in the piping which is lower than the setpoint. As you heat the water and send it through the supply line the hot water is cooled by losing heat to the ground. If you now turn on the shower the flow is back to the desired flow range, the heater works, and the temperature controls take over.

So far no responder says they have a working Watts system with a tankless hot water system without a dedicated return line. I do not believe you will find one.