Heater won’t maintain temp

[banger]

Hello
have a 2018 Pentair Mastertemp 400. Worked well till just recently. I usually run it from my phone app screenlogic where I set the temp/time/schedule. Just lately it will start just fine, heat the pool/spa to desired temp then turn off but won’t come back on to maintain that temp. I can then turn it off restart and it will come on and reheat to desired temp. A few times it will allow temp to drop 4 degrees then come on but turn off before reaching full desired temp.

example: I set temp 99, heater kicks on heats to 99 then off, water temp drops to 96 heater kicks on heats to 98 kicks off.
is it a bad temp sensor? I don’t see any error Codoes but I’ve been told my unit does not store history of older codes. Thank you for help.

 

[mas985]

Does the heater control panel show the same water temperature as the screenlogic? They use different sensors so you should be tell if something is wrong with one of them.

 

[banger]

Didn’t know that, let me check……so I ran the system to get a more current reading and yes the Pentair easy controller box show same temps as the screen logic app. Current temp 67 and set temp of 101 with the system off.

 

[mas985]

That is not what I meant. The heater has its own control display which uses a different sensor. It is on the heater itself. You may need to put the heater into local mode.

The Pentair Easy Controller is the same information as the app.

 

[banger]

Gotcha! Ok now I know where to check.

 

[mas985]

A few other questions:

Are you running the heater on lower speeds of a VS pump?

Are there any error codes in that same display when the heater shuts down prematurely?

 

[banger]

Ok, OAT is currently 66. Turned on spa with heater set to 75, heater fired up and heated water to 75. Both screen logic and heater matched temp (within 1/2 degree) once water reached 75 heater kicked off. But left the spa running for another 30 minutes and the temp on screen logic never changed even though water definitely cooled. Screen logic is still showing water at 75 even though it is not. So heater ”thinks” water is 75 even though it’s not. That’s why it doesn’t come on. So what’s broke? I guess what ever is taking the temp of the water?

-running high speed
-no error codes

 

[mas985]

So I am a little confused.

But left the spa running for another 30 minutes and the temp on screen logic never changed even though water definitely cooled. Screen logic is still showing water at 75 even though it is not. So heater ”thinks” water is 75 even though it’s not. T

So after the 30 minutes, do both the heater control panel and screenlogic still report 75F?

Where is the temperature sensor located for the Screenlogic?

 

[banger]

Yes both are reporting spa temp at 75. The Pentair control panel and the screen logic app show water temp at 75 (even though it’s not) the heater itself shows nothing since the Lights all go blank when it’s not running.

 

[mas985]

Again, the heater may need to be in local mode to show the actual temperature from its own sensor.

@Jimrahbe may have some additional ideas.

 

[ajw22]

Turned on spa with heater set to 75, heater fired up and heated water to 75.

The heater thermostat should be set at 104F. You do not use it when under EasyTouch control.

Set heater thermostat to 104F and then set EasyTouch heater set point to desired spa temperature.

 

[1poolman1]

Ok, OAT is currently 66. Turned on spa with heater set to 75, heater fired up and heated water to 75. Both screen logic and heater matched temp (within 1/2 degree) once water reached 75 heater kicked off. But left the spa running for another 30 minutes and the temp on screen logic never changed even though water definitely cooled. Screen logic is still showing water at 75 even though it is not. So heater ”thinks” water is 75 even though it’s not. That’s why it doesn’t come on. So what’s broke? I guess what ever is taking the temp of the water?

-running high speed
-no error codes

The temp sensor in the automation is, apparently, the one causing the difficulty. If it is not reading the drop in temp it won't turn the heater on. Actually, it just allows the heater to fire. The heater just "knows" that the water is 75 but the automation has opened the control circuit. The heater temp setting should be its hottest, 104 and the automation does the rest. Replace the water temp sensor for the automation. This one from Wholesale Sensors is a good one and very inexpensive. You don't need OEM unless you want one. Actually, any temp sensor for any brand that has been used in the last 10 - years will work, they are all 10K sensors.

Amazon.com

 

[banger]

Thank you. I will try that.