Pentair Mastertemp 300 Cycles on/off - no Error Codes
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Posted

I have a 3yo MasterTemp300 with the heat cycling on/off about every minute. The 'SERVICE SYSTEM' LED is not on, and no LEDs on the backside of the board are illuminated. My first guess was that the thermal regulator was not functional, but it has been replaced without success. The troubleshooting flowchart in the manual suggests that the Control Board needs replaced, but I'm hesitant to move forward without more confirmation. Any suggestions about how to proceed or other troubleshooting measures to try? Could this be an issue with the manifold bypass valve? Any help is appreciated!

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Richard's picture
Tech, Pentair
You may want to check if the
Richard's picture
Tech, Pentair
Posted

You may want to check if the exhaust temperature is exceeding 470 degrees F. To do this, while the heater is running hold down the pool or spa button down for 10 seconds, your display will change to reading the exhaust temperature. This could be board or stack flue sensor issue if the thermal regulator is opening properly, also you will want to make sure you have no restrictions in water flow, this can drive your exhaust temperature high a well.

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Thanks Richard! Just checked
Posted

Thanks Richard! Just checked the exhaust and it doesn't exceed 240F before the burner shuts off for about 30 seconds. Is this pointing to a board issue, or are there other things to check?

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I have the same issue.
Posted

I have the same issue. Heater will heat for approx 35 mins and then just cycles on and off every 40 secs. No error codes on front or back of control board. If I shut the heater for 10 mins, the entire process starts again...heat 35 mins then cycle on/off every 40 secs. I replaced stack flue sensor and hi-limit switch. This didn't help. I checked the thermostat and it opens when put in hot water. I removed the manifold to check the bypass and it is fine also. What else can it be?

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Richard's picture
Tech, Pentair
Brian, try running the heater
Richard's picture
Tech, Pentair
Posted

Brian, try running the heater and if the 35 minute shut down is consistent, press and hold down the pool or spa button down for 10 seconds in approximately 30 minutes to monitor the exhaust temperature, make sure you are not close to 500 degrees at that point, the board could be thinking that the exhaust temperature is higher than it actually is, and this could be the cause of the heater shutting down, if that checks ok, you may want to contact us at 1-800-831-7133 and speak to one of our heater technicians.

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Hi Richard, I did call
Posted

Hi Richard, I did call Pentair several days ago and received some troubleshooting advice. I'm not sure if it was you or not I spoke with on the phone, but in any event my problem is solved. Thank you to the tech and the entire Pentair team!. Long story short, I was advised my symptoms sounded like a water flow issue. I bought a $5.00 tube of silicone and with the pump running lubed up all the low pressure joints. Just outside of the pump as I was applying the silicone I felt it suck up a little of the silicone right into the joint. The old cement there had become a little rough and cracked. Immediately I noticed the air-gap that was consistantly at the top of the pump strainer disappear. My heater now stays on without cycling. I can only surmise that the air leak would fill up my filter after 35- 40 mins of run time and cause my water flow to fall below the minimum spec causing the constant cycling.
Other symptoms that I ignored were the above mentioned air-gap, and air bubbles from my return jets. I just assumed that if the filter worked for 30 mins it couldn't be a flow problem but I was wrong. It seems that many people are having this same cycling issue. I hope this info helps

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I tried the low pressure
Posted

I tried the low pressure check on mine, but it didn't end up being an issue. At this point I've also replaced the control board and membrane pad without luck. The natural gas pressure was also checked at the heater during operation and showed 8 inches WC.

We've ordered a few additional parts to check next:

> Ignition Control Module
> Ignitor and gasket kit
> Flame holder kit

Any thoughts if we're on the right track here or is there something else we should be checking?

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Did you check the bypass
Posted

Did you check the bypass valve in the manifold? It is just a plastic retaining clip inside of a spring. If it breaks you will have very little flow thru the heater coil. I don't know why this doesn't cause any LED's to light, but it seems to be a common problem. I got lucky with mine and the fix was something I never expected. I hope the same happens for you. Good luck

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