I have a 10 year old Pentair Master Temp pool heater that makes a rattling noise when the heater is running. The burner comes on okay and stays on until it is manually turned off. When the heater is off the rattling sound disappears. Water flow is always directed through the heater, there is no manual bypass. I removed the manifold and disassembled it. Aside for some scale, everything appeared to in order including the sensors. I cleaned it up and reinstalled the manifold but the rattling noise still persists.
I have taken over the task of testing the water for CL2, PH and Total Alkalinity. I found the free CL2 level to be 4 ppm but the PH is above 8.2 PPM and Total Alkalinity is about 220 ppm. I’m currently adding Muriatic Acid gradually to lower the PH.
Could this issue be a malfunctioning bypass valve? The burner is putting out the heat but it’s not transferring to water return to the pool. Any ideas?