New Raypak LP heater issue. high limit fault

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You can easily test your limit switches the way I did. Suspend the switch in water so the base is in the water but the terminals are out of the water. Clip an ohm meter to terminals and heat the water while you monitor the temp. I’d also clean and apply fresh thermal compound when reinstalling. Something similar to CPU heat sink compound used on a computer’s CPU.
 
Really good information, I think this is likely what has been causing my ongoing hi limit 2 fault issue. Seems Ray Pak tried to address it with the addition of the heat shield as I do not believe I have that part on mine, which I got in 2015.
 
I have ordered a heat shield. I plan to install it along with a new Hi limit 2 sensor (with thermal paste). Am waiting on the bypass as its a more complicated job and I'd rather rule out the obvious first. There was no high limit issue yesterday, but it was back again today. Seems like it gets me at 103-105 almost every time.
 
Even with the shield I had issues. It was every time I fired it up also. That side of my heater also faces directly into the sun for most of the hot time of the day. You lean on the enclosure with the heater off and it is friggin hot! I have a bypass valve for the heater. So my pump does not have to be pushing water through it all of the time. With the heater powered on, but not heating of course, Isolated the temp reading on the display will hit 106F with no water flow through it. It must have gone over that during the heat wave because I have seen a "sensor failure" message on the display when it was isolated. I asked them what that meant and was told the temp reading was above its reportable range. So yes, it is hot in there. I believe the addition of the thermal compound (and it does show there should on those limit switches on their drawing) and the additional heat wrap I put on the shield made all of the difference. I have had zero issues since then. My thermocouple doesn't lie. :)
 
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Yes, that's the sort of stuff I used. I had a Jegs brand from years ago left over from my car headers. Its not the easiest stuff to work with on flat metal. That is why I riveted it with large washers.
There may be other basic insulations that work just as good.
I'd clean out where the switches mount and apply fresh thermal compound as well. That stuff does dry out. On high performance PC's they have to replace the stuff on the heat sink every few years.
I use Artic Silver 5 thermal cooling compound paste. You only need a tiny dab of it.
 
I took off the cover today as you suggested. No high limit error. I think that you and @1poolman1 nailed it about needing better insulation. I am just amazed that the problem presented for me after no issue for 10 years.
 
I just installed two new high limit switches (only #2 had acted up but they were $20 each so why not) using fresh thermal paste. The existing paste look then and dry.

I’ll report back after a few days whether high limit 2 trips or not. I also plan to insulate the shield, but still waiting on usps for remaining items
 

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Did not take a few days. Just a few hours. Got another high limit 2 error the first time it heated after inserting new sensor.

Next up is the insulation on the heat shield. Part arrives on Monday.
 
Thanks for the update, please keep them up and I will likely follow suit. Now that it seems my hi limit fault doesn't indicate a problem with the heater I can be patient as it doesn't materially impact the performance... I still get 2 degrees per hour and it sure helps that I have no spa so thus never set to the temps that you do.
 
Well that is a bummer.
Have you also tested that internal "unitherm governor" Fancy name for a thermostat. Just like a cars thermostat.
I yanked mine and suspended it with a coat hanger in a pot of water on the stove with a thermometer in there to see when it opened. They are rated at 105F. Mine opened up at that temp as was fully open soon after that so I knew that was good also.
You only have a few things that can go wrong there.
Insufficient water flow
bad temp governor
bad switches
overheating the switch area.
When you get the fault, do you just have to let it cool off and then reset it? The switch is definitely "open" at that point? meaning the thermal contacts have opened up and breaking the circuit? Its important to know if the fault is real.
 
When I get the fault, the unit says “press mode to reset “. Pressing mode moves unit to off so I press twice to go back to spa. Heat comes on immediately. Usually fault at 104-105, I reset at 101 (so it has cooled slightly). I inspected UG visually and it looked ok
 
Happy update: I put the insulation on top and bottom of the heat shield as a trial today. Did not get a high limit 2 error. Will see if my luck keeps up. Bad news is that my pool heater started giving me a ILO error. I may swap boards with spa heater to test.
 
How do you visually check the UG? They all look the same when removed and closed. You can only tell if they work properly if you test them in hot water at their opening temp rating.
You heat the spa to 104/105?
that’s hot! I don’t know if I could get my foot in there. 🙂
I go to about 99 or 100.
 
The UG had many pine needles in the spring. I removed them. The part did not look rusted at all - that was the visual check. In any case, the High Limit 2 situation has gone away for two days at least with the insulation. Thanks for the idea.
 
I made it six days without high limit 2 fault. But the 7th day was not a charm as it came right as the water read 106 (set to 107). I ordered a replacement bypass and the gasket for the header and will bit the bullet and open and replace.
 
Personal preferences aside, just wondering how you set your spa to 107F?
I thought the max temperature for a spa was 104F to be considered safe for adults to enter. My heater will not even accept a setpoint above 104.
 
You can change high limit for pool or spa to 107 through the service menu (need to press button on circuit board for 5 seconds to enter). 106-107 at the heater corresponds to 104 in spa. The Raypak thermistor is a bit inaccurate
 

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