Pentair Mastertemp 400 - Ghost in the Machine - Membrane Pad?

CaptainUnderpants

0
Bronze Supporter
Aug 14, 2017
43
Long Beach, CA
The heater works, then it doesn't work. Runs for 5 minutes, then shuts off and tries to turn on then sometimes successful, sometimes not. But no error codes. Hmmmmmmm. What could it be? It is very hard to diagnose an inconsistent problem. However at this point, I am pretty Dang sure it is the Membrane Pad. I have one on order and will be able to replace it tomorrow to confirm my suspicions.

Recently I replaced a broken manifold bypass valve. My first repair to my 5 year old heater. The symptoms were simple, turns on, runs for 30 seconds and then shuts off. Very consistent behavior. The current symptoms however, are all over the place. Note: my system is controlled by a Pentair easytouch system.

Several examples of wonky behavior that leads me to the membrane pad are: When the heater does run on the spa setting, it shuts itself off when the system, by itself switches to "Pool" at the Mastertemp membrane pad. My phone app linked to the Easy Touch system however, still says that the Spa is on and light at my Spa panel, just above the waterline on the spa wall is on, even though the Mastertemp heater shows the pool light on. Sometimes I see the pool light flicker before it finally switches to pool mode which turns off the heater.

A second symptom is that the manifold temperature displays instead of the spa temperature. At first I thought this high and rising number was the actual water temperature reading and there was not enough water flow to cool the system and that why is was shutting off. However, when the system does run and stays on, I see this number climb until it reaches around 320 degrees. From reading posts, manifold temperature is displayed instead of spa temperature by holding down the spa button for 5 seconds. This leads me to believe that the spa button is shorting out for the manifold temperature to be displayed. Finally, some of the buttons such as temp up/down are unresponsive.

I sure do hope that this is the problem as I have ordered numerous other replacement parts based upon mis diagnosed symptoms. Anybody else get "Wonky" behavior from their system as a result of a membrane pad going bad?
 
Last edited:
Did you check your ground connections to make sure they are clean? Your situation sounds more intermittent and so hopefully changing the membrane pad will work. But also check the flame sensor current (which runs to ground) because a bad ground connection can cause a low flame sensor current which then shows up as an ignition failure lockout. It seems like the Mastertemps are prone to developing bad ground co facts over time.
 
Did you check your ground connections to make sure they are clean? Your situation sounds more intermittent and so hopefully changing the membrane pad will work. But also check the flame sensor current (which runs to ground) because a bad ground connection can cause a low flame sensor current which then shows up as an ignition failure lockout. It seems like the Mastertemps are prone to developing bad ground co facts over time.
If the problem still exists after replacing membrane pad, that will be next to check on my list. Thanks!

Quick update - After Tennis today I wanted to use the hot tub (Spa). Put on the heat and the same thing happened, it starts and kicks off after the Spa light switches to the Pool light with no input from me. The Pentair Easytouch system see the spa on and all of the flow controls are set to Spa mode, yet the Pool light is on the Mastertemp Membrane panel. At that point I have a flash of brilliance and raised the temperature on the Membrane pad to the point where the heater will kick in. Bingo, the manual override works and the heater kicks on. I think this sound like another scenario that points to a bad Membrane pad. New membrane pad delivery scheduled for tomorrow!
 
Conclusion - The new Membrane Pad came today. I plugged it in and problem solved. The Pentair Mastertemp 400 heater turned on and stayed on with no weird gremlins. Ran it for several hours on both the spa and pool mode with no hick ups.

As a preventative measure against future failure, I put a small bead of clear silicone around the edge of the membrane pad to eliminate water seeping between the layers. From what I have read membrane pads often need replacement from water intrusion. My heater is 5 years old and this seems typical. Hopefully this will extend the life.
 
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.