WF Series 7 Desuperheater E15 HW Limit Faults

My WF Series 7 keeps having Desuperheater E15 hot water limit faults. I have had the thermostat and the Series 7 unit software upgrades a month ago. It was my understanding that one of the issues that was to be addressed by the unit software upgrade was these faults. I have only about 40 hours of runtime since the upgrade and now have over 300 faults.

The DSH setpoint is 130 degrees.

I have purchased an AID tool and can monitor system performance and faults. If it wasn't for the AID tool I would not even know about the faults, except something does not seem quite right about the hot water the system produces.

I am monitoring the the temperature of the in and out lines of the desuperheater and my water tank. None of the readings are any where close to 130 degrees.

Have any of the installers noticed this issue?

Thanks,

 

Is your DSH loop properly bled/burped?

 

Good question Joe,

I know it was bleed when installed. I think there is a way to bleed it from the top of the pump during operation.

I pulled this from the installation manual. Will this be good enough? Maybe it should be done several times over a couple of days.

Use an AID Tool to enable HWG and select the desired water heating set point. Selectable set points are 100°F – 140°F in 5°F increments (default 130°F). From the Main Menu of the AID Tool select Setup, then AXB Setup
12. Turn on the unit to first stage heating..
13. The hot water generator pump should be running. When the pump is first started, turn the venting (burping) screw (if equipped) in the center of the pump two (2) turns open until water dribbles out, then replace. Allow the pump to run for at least five minutes to ensure that water has filled the circulator properly. Be sure the switch for the hot water generator pump is "ON".
14. Allow the unit to heat water for 15 to 20 minutes to be sure operation is normal.

 

shouldn't have to bleed more than once. Where's your installer?

 

Installer is about 45 minutes away. He is fully aware of the issue and has talked to WF before my updates. They told him the unit update was to address this issue. Since the update the issue continues. He has been notifed again and was going to talk to WF again. Waiting on a reply.

Was hoping WF would reply to the issue on this forum???

 

All the things I can think of:
- it's shutting off properly at temp, as it should
- no circulation
- the temp at the limit switch is not representative of the circulating fluid
- faulty limit switch
- and then, some programming issue

 

I had a temp sensors not working properly, not on the DSH, but I believe they are the same sensor. Exchanging the sensor did the trick.

If the heatpump has not enough run time or runs in lower stages, the DSH will not get up to 130F.

 

josephparris,

The hot water limit E15 code is not a fault. This alert indicates that the desuperheater high limit has been reached. This code should also appear on your thermostat. Once the tank cools off, hot water generation should resume. If the hot water temperature has not reached 130[SUP]o[/SUP]F, we would suggest contacting your dealer for further assistance.

As for the software update, this was done to correct issues with the energy monitoring. If you have an IntelliZone2 zoning system, this software update also corrected an issue with the emergency heat.

 

Thanks WF.

The alert DOES NOT show up on my thermostat. I have temperature sensors on the "in" and "out" lines of the desup, and also on my hot water heater. This issue was noticed before the update. I had two updates, one to the thermostat and one to the unit itself. I was told that one of the issues that the unit update was to address was the E15 "alert" (The AID tool reports it as a "fault").

I have attached a graph from the past two weeks showing EWT, LWT and Hot Water Heater Temps. As you can see when the system is idle the EWT does rise higher than the leaving.

 

You don't have a buffer tank? Your tank temperature is dictated by the electric heat element, not the DSH. Your desuperheater will not contribute much to your hot water generation if you do not have a buffer tank. Wrong setup.

 

You are correct, no buffer tank. The more I read, the more I am now realizing I need a buffer tank to take advantage of the hot water generation. I have put that on my "to do"list for the near future. That still does not explain all the E15 faults. I heard from my installer today and they are going to replace the sensor.

i have a fairly new hot water heater, can you suggest a buffer tank?

 

The "faults" sound like they are not faults. Sounds like they are the limit switch shutting off the DSH. Which it is supposed to do.

 

I would hold off on the sensor exchange. Your DSH is fed hot water by the hot water tank and the sensor turns off the circulatns pump. Your monitoring indicates that the control board turns on the DSH circulation pump after it samples the temperature. It seems to do its job!
Now why they put in the most efficient forced air heat pump on the planet and installed it with the least efficient setup for DSH (single tank), which ensures that the DSH will hardly turn on (thanks for documenting this so nicely!)? Beats me!

You need a buffer tank! Badly!
Here is the 7-series setup with a buffer tank.
Temperature and Energy logging by: Web Energy Logger

 

Because Waterfurnace says they can. In this application the heat pump documented that the element in the water heater did it's job and thus the DSH could not contribute.
Someday maybe some manufacturer will have the stones to say the one tank set up doesn't work.

 

Here is an update:

Installer came out today and replaced the sensor. Minutes after replacing, E15 fault came again. Then a call to WF, they said the system was operating correctly since the water being pumped back to the desup was hotter than the output. Which makes sense and the graph above proved it. They said it would not work correctly without a buffer (there's that word again) tank. Exactly what you guys had been telling me all along. So why did it take them that long? Oh well.

So, buffer tank it is and hopefully the limits go away and I am able to take full advantage of the desup system.

Thanks for all your help and expertise. I'm off to Lowe's

 

This is an open letter to Waterfurnace and all the other heatpump manufacturers:

"Please do not anymore endorse a single tank desuperheater setup as an option in your installation manuals. As discussed here multiple times, and now nicely documented by one of your customers, a single tank defeats the purpose of the desuperheater, namely to preheat the domestic hot water, since it competes with the electric heat element in the single tank. This will result in inefficient operation, unhappy customers and unhappy installers (because of unhappy customers). Please either show people how to pipe a dual tank setup (what you do) or no DSH at all. But please do not endorse a setup which results in an increase in installation costs and lacks any beneficial performance."

 

Right out of the installation manual.

 

There is one person on here, I think Geome, that uses a timer on his single tank set-up. So elements only fire at certain times.

Chris

 

You can also have a timer on a second final tank, so it tops off your hot water only when you need it. It still does not change much

 

There are many things in our industry assumed to be true and certainly the one tank installation is one. It is funny that manufacturers are disinterested in measuring actual performance of their designs or they would not continue to recommend this.....and they all continue.