I'm at my in-laws at my father in law has a pool with a Pentair MasterTemp 300 pool heater and it won't stay lit. It turns on and runs for 30 seconds or so but then goes out and the "Service Heater" indicator goes from green to red. No error codes are displayed. Tried blowing out the air intake and exhaust to ensure there's no obstruction, but there's not much else to go off of. Odd there's no error codes like the manual indicates there could be when there are problems. Any suggestions?
Help with a Pentair MasterTemp 300 that won't stay lit
- Thread starter BlueWRXPride
- Start date
Thanks. I tried a few things but no luck yet.
- Found the Fenwell LED light and it gives 3 flashes indicating no flame being sensed and ignition being locked out
- Checked the ground wire from the Fenwell control panel which went through a wire nut to the control panel box and saw it was quite corroded. I clipped that bit off and stripped some fresh wire, and then made my own ground to the chassis, but no change in symptoms.
- I tried measuring the FC+ and FC- probes and not no voltage regardless of if the flame was lit. I suppose this could indicate a bad flame sensor, but it was hard to be sure I had good contact with the pins so I'm not certain of that information.
I also want to add that I see none of the error LEDs on the backside of the control panel lit at any point.
Seems like a flame sensing issue.
Check the ignitor and the inlet gas pressure static and dynamic.
Check the ignitor and the inlet gas pressure static and dynamic.
I don't think it's the igniter, for the 20 seconds or so that it runs the exhaust definitely gets hot. I'm not sure how to check the inlet gas pressure, but the tank was just filled up a few days ago so I'm sure we're not low on propane
Alternate Ground Circuit.
Fenwal ground problems are common enough that Pentair has a ground wire kit for the MasterTemp and Max-E-Therm heaters (KIT P/N 475214Z), and Fenwal has a technical article on "Improve Grounding in Gas Ignition Controls"[11].Pool heaters often have a lot of ground wires that run from every different part of the metal firebox and sort of daisy-chain back to the control system ground. Problem is that severe service combined with a few small leaks can leave the heater a corrosion mess in short order.[12]
The ground system is a very critical component for heater control since it works by producing a tiny signal to ground and then the control module detects it to be sure there's a flame. This technology is incredibly reliable so long as the ground system has no interference from corroded wires. If it doesn't detect this tiny signal (about 2 millionth's of an amp) due to corrosion the system will keep the gas valve closed.
To positively fix this you just run a wire from the burner base or from the burner flame holder on many of the new high efficiency heaters to the ground connection on the control module.