I have a Pentair Mastertemp 400 that I can’t seem to figure out why it’s cycling. Initial startup fire ups nicely and will run anywhere from 4-7 minutes then shut down and cycling begins. Cycles will be about a minute and willl continue to do so nonstop. Heater will just keep going like this. I’ve checked the manifold, the thermal regulator which opens and closes in hot cold water. I’ve replaced the the thermistor and I don’t get any service lights or leds on back of board or the fenwall. Filter is clean and pressure is good. Worked fine last season and started up this way on opening this year. This is my 4th year with pool. I have a fenwall on order thinking either that or board. Only reason I’m thinking fenwall is that it keeps cycling and won’t lockout. Can you still have a bad thermal regulator that still opens closes?
Mastertemp 400 cycling No codes or service light
- Thread starter Bryanlaw07
- Start date
Be sure your gas supply is correct. What size gas meter to your house? As heater age it makes a big difference. Also try this thread:
MasterTemp 400 Failure To Ignite Issue - SOLVED
- Jul 21, 2013
- 66,092
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
I think you mean...
MasterTemp 400 Failure To Ignite Issue - SOLVED
I wanted to document this on the forum threads since this issue got diagnosed and solved via PM. First, let me give total credit to our esteemed forum expert @JamesW for helping me to diagnose, test and fix this heater issue. James' help saved me from calling in a "pool service" guy and...
www.troublefreepool.com
As a test try and run the heater without the thermal regulator in and see if it behaves differently. Thermal regulators that test good may still not respond correctly.
You need to open the header and check the bypass valve.
Pentair MasterTemp Heaters - Further Reading
www.troublefreepool.com
What water temperature is displayed on the heater control panle when the cycling starts? Is it always around the same temp?
I believe I have a large enough meter, 630 meter which is same age as pool. The temp on display has been accurate as we have had a few hot days and some cool ones . Today EasyTouch has pool at 74, Mastertemp is saying 75 and I have it set for 89. I removed the thermal regulator and it behaves the same. 3 1/2 minute initial firing then cycling began with 1 minute cycles. No codes. I inspected the bypass valve and it appeared fine. Clean no obstructions.
- Jul 21, 2013
- 66,092
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Does the heater make any knocking noises before it shuts down?
The water in the heater is overheating and one of the safety sensors is shutting it down. When the safety sensor cools it resets and the heater fires again. Thus the cycling.
You either have an external flow problem with not enough flow through the heater to carry away the heat generated or you have an internal water flow problem which is regulated by the thermal regulator and bypass valve.
You are at the heater and we are not. You can observe. We can only guess.
Have you opened the top and flipped the PCB over to observe the diagnostic LEDs and see which one may blink when the heater shuts down?
How did you inspect the bypass valve?
The water in the heater is overheating and one of the safety sensors is shutting it down. When the safety sensor cools it resets and the heater fires again. Thus the cycling.
You either have an external flow problem with not enough flow through the heater to carry away the heat generated or you have an internal water flow problem which is regulated by the thermal regulator and bypass valve.
You are at the heater and we are not. You can observe. We can only guess.
Have you opened the top and flipped the PCB over to observe the diagnostic LEDs and see which one may blink when the heater shuts down?
How did you inspect the bypass valve?
Sometimes the led light on the back of the board just shows briefly when it shuts down. Make sure temp on heater is set to max temp. What’s the sfs temp?
No it doesn’t make any knocking noise or any noticeable sound before it cycles off. I inspected the bypass valve by physically removing the manifold and inspecting the inside. And I’ve watched the back of the board to see if any lights flash on when it cycles off and no leds come on.
The only thing I did wrong that might have started this was I opened the pool two weeks ago. I use the ScreenLogic app and I wasnt home and tried to start the heater through this as I usually do. Only thing was I never opened the gas valve and noticed this when I got home a few hours later as the service light was on.
can you post pics of the equipment? You may need a manometer to check wc. Does the fenwal blink? Did you run it long enough to clear any void in the gas line?
It doesn’t look like you have an external bypass. If all temps on ScreenLogic and heater are accurate. I’m leaning towards a disruption of gas flow, bad ground flame rectification. Unless there is something else you can think of. Does the heater gas line have its own regulator? I’m stumped your system says internal flow problems but no sensors to agree. Let’s see if @JamesW has any ideas
The gas line does not have its own regulator. So at this point I’ve replaced the fenwall and the thermal regulator and no luck. I just didn’t think it was going to be a gas issue because the way it runs on the first startup anywhere to 4-8 minutes cleanly and then short cycles of almost exactly a minute. Just thought something was getting to hot or overheating. Is there anything else I can check before I call someone? I appreciate the responses and the help so far, thank you. Maybe I’ll try bleeding the gas line
One check valve from the pic looks like it’s not even open and the other looks like water is running through. What rpms are you running the heater?
I might not of had it running during the time of the pic but I opened up the check valve and it’s good. Pool is running at 3,000rpm
Checked and tightens all grounds and I tried a new board still having same issue and No codes on the new board either. Could it be a bad flame sensor. It’s igniting fine maybe just not reading it properly. I blew into the air flow switch hose and can hear it click on so that’s working. If not sounds like I’m having a gas issue of some sort but nothing has changed, big enough meter and has ran fine for 3 years.
The hsi alternates between igniting and flame sensing. I wouldn’t change anything else until you check gas wc. You’re looking for a static drop under 4” wc.