Pool heater is working but not heating water

[Aigs92]

I’m hoping someone here might have some good advise for figuring out why my pool heater is not heating the water.

I have a Jandy JXi gas pool heater (similar to the one pictured). The heater turns on and fires up. The blower is working and there is heat coming from the exhaust (it’s acting the same as it always has). But, the water coming out of the jets and water fall is not in the least bit hot. Almost as if the water is flowing through an internal bypass (there is no external bypass) and not through the heater. This is where I’m stuck.

What would cause this and how would I troubleshoot it to determine the cause? Any input would be greatly appreciated. Thanks!

 

[ajw22]

Welcome to TFP.

What you are describing cannot happen. If the heater is on it is generating BTUs of heat. The heat MUST be absorbed by the water or go up the exhaust. If the heat is not absorbed by the water the heater will quickly overheat and its safety mechanisms will shut it down. Otherwise your heater would have melted by now.

What BTU rating is the heater and how many gallons are in your pool?

What is the GPM flow though your heater?

Depending on those answers the temperature rise at the pool retmay not be much but the BTUs are getting into the pool.

Is this pool new to you?

Heater Maintenance - Further Reading

www.troublefreepool.com

 

[Aigs92]

Thank you for the warm welcome! The pool is fairly new to me (1 year) and it’s my first pool so I’m green behind the ears to say the least.

That was my first thought, “this doesn’t calculate”. I will address a few of your comments. First, I didn’t leave the heater on for more than about 5 minutes because I thought the same thing; I don’t want to burn it up. The exhaust got hot to the touch pretty quick.

Unfortunately, I’m not sure of the BTU rating (I can’t seem to find the actual model number of my unit) but all of the models that look like this one have a GPM min of 30 and max of 100.

In the year we have had the home / pool, we have used the heater dozens of times, mostly when it’s pretty cold out. We have a waterfall as well, and then the heater is on, the water coming out of the waterfall is hot (my kids congregate around it for this reason). But now, with all other factors the same, the water coming out is still cold. I am beyond puzzled.

 

[ajw22]

How many gallons are in your pool?

@PoolGate where is the BTU rating label on the JXI heater?

 

[Aigs92]

I’ve been told by a pool company that came to replace something when I purchased the house that it’s 25K - 30K gallons.

 

[Toxophilite]

Thank you for the warm welcome! The pool is fairly new to me (1 year) and it’s my first pool so I’m green behind the ears to say the least.

That was my first thought, “this doesn’t calculate”. I will address a few of your comments. First, I didn’t leave the heater on for more than about 5 minutes because I thought the same thing; I don’t want to burn it up. The exhaust got hot to the touch pretty quick.

Unfortunately, I’m not sure of the BTU rating (I can’t seem to find the actual model number of my unit) but all of the models that look like this one have a GPM min of 30 and max of 100.

In the year we have had the home / pool, we have used the heater dozens of times, mostly when it’s pretty cold out. We have a waterfall as well, and then the heater is on, the water coming out of the waterfall is hot (my kids congregate around it for this reason). But now, with all other factors the same, the water coming out is still cold. I am beyond puzzled.

I might just be relative to when you previously felt of it. If you started with 50-degree water, with size of heater and flow at best case, you would only get output water about 65-degrees. That's kinda hard to discern in difference by just hand-feel. Plus, even that is blending as it exits.

 

[Aigs92]

I might just be relative to when you previously felt of it. If you started with 50-degree water, with size of heater and flow at best case, you would only get output water about 65-degrees. That's kinda hard to discern in difference by just hand-feel.

I see your point; I did not think of that and don’t have a good reference point to go by (I never pay that close attention to the water temp). The water temp is at 66 today (I’m in central Florida). I guess my question would be, in a gas heater, if water goes in at say 66, what temp would it come out at? On a winter day (given a Florida winter day), I can heat my hot tub to 100 degrees in just over an hour.

 

[Aigs92]

Here is a picture of the pool for size reference if it helps at all.

 

[Toxophilite]

I see your point; I did not think of that and don’t have a good reference point to go by (I never pay that close attention to the water temp). The water temp is at 66 today (I’m in central Florida). I guess my question would be, in a gas heater, if water goes in at say 66, what temp would it come out at? On a winter day (given a Florida winter day), I can heat my hot tub to 100 degrees in just over an hour.

My hot tub is 550 gallons (bout your sized), and I could heat from 60's to 104 in about 30 minutes with 400K heater. So, you might have smaller heater at play. But, when I first would run it for that, exit water from jets would not start to even register heat on my hand for a good bit beforehand. Maybe start to notice warmth after 10 minutes or so, then, it starts to register a bit faster and faster by feel alone. As for actual heat to spa, the temp climb for entire volume is at a pretty constant rate.

 

[ajw22]

Did you read this?

Heater Maintenance - Further Reading

www.troublefreepool.com

 

[JamesW]

Remove the front door of the heater and show the label.

Can you show the system?

 

[Aigs92]

Did you read this?

Heater Maintenance - Further Reading

www.troublefreepool.com

Wow, that was really helpful, thank you. Tomorrow I will give it some more time and hopefully be able to chalk this up to me being too impatient (and save money on a service call). I’ll report back and let you know. Thank you again for the help!

 

[Aigs92]

Remove the front door of the heater and show the label.

Can you show the system?

I will tomorrow once I have some sunlight. I got dark on me before I started posting anything and didn’t think to take pictures.

 

[setsailsoon]

I think my label was under the top cover. Assuming you have the 400K BTU per hour unit and making a guess on the flow rate range your water temp from inlet to discharge of the heater should increase about 5-15 deg F. Water coming out won't feel hot. Temp rise for the pool of 1-2 deg/hr is typical. Let it run a couple hours and check the pool temp before and after. Sounds to me that it's working based on your description above.

Chris

 

[JamesW]

Assuming an 84% efficiency, a 400,000 btu/hr heater will deliver 336,000 btu to the water in 1 hour.

At 40 gpm, the total amount of water going through the heater in 1 hour is 2,400 gallons or 20,016 lbs.

That will create a temperature rise from inlet to outlet of 16.8 degrees Fahrenheit. Assuming an inlet temperature of 58 degrees.

Gpm.....rise....outlet
40........16.8......74.8
60........11.2......70.6
80..........8.4......66.4

 

[JamesW]

A 400,000 btu/hr heater with an efficiency of 84% transfers 336,000 btu per hour to the water.

At a minimum required flow of 40 gpm, there will be 2,400 gallons of water (20,000 lbs.) that receives the heat.

Each btu raises the temperature of one pound of water by one degree Fahrenheit.

336,000 btu into 20,000 pounds of water is 16.8 degrees of temperature rise (336,000/20,000).

So, the maximum temperature rise you should ever have is 16.8 degrees Fahrenheit.

Higher flow results in a lower temperature rise.

50 gpm = 13.44 degrees temperature rise.

60 gpm = 11.2 degrees temperature rise.

70 gpm = 9.6 degrees.

80 gpm = 8.4 degrees.

 

[JamesW]

This shows the expected temp rise (Y-axis) vs. Flow in GPM (X-axis).

The minimum required flow is 40 gpm.

So, the maximum temp rise should be 16.8 degrees Fahrenheit.

What is the flow rate?

 

[JamesW]

30,000 gallons is 250,200 lbs of water.

336,000/250,200 = 1.343 degrees per hour pool water temperature rise.

You also have to account for the heat lost, which increases as the water temperature increases, especially if the pool is not covered.

If you lose 1 degree per hour, your net gain is only 0.343 degrees per hour.

 

[setsailsoon]

James,

Thanks much for your usual complete math and science. I noticed they had an enclosure which was very similar to my installation. So the math should be similar. I'm guessing the enclosure greatly reduces wind velocity over the water and thus heat loss by evaporation also. I typically got 1-1.2 deg/hr.

Chris

 

[JamesW]

I typically got 1-1.2 deg/hr.

Your pool volume is half of the OPs.

What is your heater size?