Water from Jandy Jxi heater not getting hot

[jono2330]

I have a Jandy Pro Series Jxi 400 heater that fires up and seems to be running fine, with no error codes, but the water coming out of the spa or pool jets is warm, at best. Even after running for 10-15 minutes. Unit is 2 years old and has not seen much use. When unit was working properly, last year, it would take the spa approx. 45 minutes to reach 104 degrees. Could this be a TRV valve malfunction, or temperature sensor issue?
Any thoughts be would be appreciated!

 

[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]

Check the amount of natural gas used per hour.

The gas meter should show 400 cubic feet used per hour.

 

[JamesW]

What is the volume of the pool and spa and how many degrees does each gain per hour?

 

[jono2330]

High James, thanks for the quick reply. Out of town for a couple of days so just getting back now, to answer your questions, best I can. Flow rate to spa 75Gpm. Small spa 6x7 with an approx. average depth of 3 feet so your looking at approx. 126 volume. I have really no way of monitoring the propane cubic feet, as it is a large propane tank, and an hour usage is a mere blip, and honestly at this point a waste of propane. Let me again mention, when the spa was working properly last year, it would heat to max. 104 degrees in 35-40 minutes. Max. The most I have let it run this year, in trying to diagnose the problem, is 20 minutes and the temp. in the spa rose 2 degrees (75-77). The heater seems to be working properly, fires up with no problem and the exhaust air is very hot. Measuring the water temp coming directly out of the spa jets never exceeds 87 degrees when running for 20 minutes. As mentioned, no error codes. Could this be a TRV valve issue or temperature sensor issue?
Thanks again for trying to help

 

[JamesW]

126 cubic feet is 945 gallons or 7,843 lbs of water.

Using the graph at 75 gpm, the temperature rise from inlet to outlet should be about 9 degrees.

Assuming 82% efficiency, the expected temperature rise in the tub should be

400,000 X 0.82 ÷ 7,843 = 41.82 degrees per hour or 0.70 degrees Fahrenheit per minute.

In 20 minutes, you should get about 14 degrees.

 

[jono2330]

Exactly! Which brings me back to square one! I am getting only 2 degrees in twenty minutes, and I doubt if I would get a higher temp in 40 minutes, as water goes over my spillway into the pool when using the spa. Remember also that the water coming out of the spa jets, never gets hotter than 86 degrees, running 2 minutes or 20 minutes! The question is why! Any thoughts about the TRV valve or temperature sensor??

 

[JamesW]

as water goes over my spillway into the pool when using the spa.

Are you in spillway mode or spa mode?

If you are having water continuously spilling over, then you are heating the pool too.

 

[JamesW]

spa jets, never gets hotter than 86 degrees

At 75 gpm, the temperature rise from inlet to outlet is 9 degrees.

If the inlet temperature is 77 degrees, then 86 degrees is the expected output temperature.

 

[PoolGate]

The heat is going somewhere. I suspect there is a valve not working properly and directing water to the pool.

 

[jono2330]

At 75 gpm, the temperature rise from inlet to outlet is 9 degrees.

If the inlet temperature is 77 degrees, then 86 degrees is the expected output temperature.

Thanks James...Problem resolved!! Your mathematical calculations, and spillway thoughts put things in perspective, combined with PoolGates comments, directed my attention to my valves. The Jandy valve actuator on the drain side of the pool plumbing was in the center "lock" position from when the pool was closed by pool company. It was simply a matter of flipping the switch from off to 1 which opened the valve to the spa drain, and closed those from the skimmers and main drain. Water no longer went from spa over spill way to pool and spa went from 74 to 90 degrees in no time!! Thanks again for all your help and patience! troublefreepool.com rocks....time to make a contribution!!
Thanks again John