Any other options before I drop $700 on a new Max-E-Therm heater core?

[fatdogsdaddy]

I have a Max-E-Term 400k BTU heater that once it reaches the high 80’s it begins to shut off the burner, throws a check heater light for about a minute then the heater re-lights for a minute or so and the process repeats again and again. I looked under the panel and it is throwing an HLS light when this happens. I have gone through the forums and this is what I have done so far.

I checked the high limit switch with multi-meter and it opens at 135°.
I checked the thermal regulator and it opens at 125°
I replaced manifold bi-pass valve ( the old one seemed fine, I couldn’t see any difference between old and new).

Flow issue checks: I used a rubber bladder de-clogger that attaches to the hose and blew out the skimmer to pump line thinking something could have been stuck, replaced the filter cartridges in the filter and cleared the metal basket in line in front of the in ground pop ups manifold.

For the first 8 or 9 years of the pool before I became a TFP devotee,wasn’t the best at watching my chemicals, Las Vegas has pretty hard water and I was concerned I may have scaled up my heater coil. I tried descaling the heater coil by recirculating an acid water mix through the heater like this (

). I didn’t see anything to crazy come out and I haven’t had any scaling issues elsewhere else in the pool.

I have ran my heater after doing these steps and it continues to cycle on and off once it reaches the high 80’s. From what I have read on the forums leads me to believe a new heater core is my next possibility. Is there anything I am missing, others steps to try or a way to test the heater core before dropping $700 on a new one only to find it was something else?

 

[setsailsoon]

There are a number of other failure modes with your symptoms. Check the temp thermister if you haven't already done so in addition to the temp limit switches. There are several others. I would not buy a new tube bundle until you confirm there's water leaking into the fire box or at the manifold. Remove the igniter and use a wooden dowel to check to see if there's a water level inside the box. After you do that remove the manifold and check to see if the tubes are badly corroded. The tube bundle is the most expensive component so be sure to positively confirm a leak before you remove it.

I hope this helps.

Chris

 

[fatdogsdaddy]

I figured out the problem so am sharing in case someone else is having similar issues and finds this while researching solutions.

My builder placed a crossover pipe with a valve (I call it the mixing valve) between the inlet and outlet lines of the heater. It allows you to introduce some of the heated water from the outlet side back into the inlet side of the heater. This had been turned full open allowing too much heated water to return to the inlet and with a simple turn of the valve to the closed position my problem went away. I hate that I spent hours researching and tinkering with the heater for a simple turn of a valve but Dang sure happy I didn't buy a new core.

Any idea when or why you would need to mix some heated water back into the inlet?

 

[ajw22]

That sounds like a Heater Bypass. Many heaters have a maximum flow rate, like 70 GPM, and above that the heat exchanger can erode and be damaged by excessive water flow. The bypass allows your to set how much water goes the heater and how much goes around it.

Post pics of the plumbing around the heater.

Heater Bypass - Further Reading

www.troublefreepool.com