I've been living with a persistent high limit fault on my RAYPAK 406 water heater for at least six months now. When I turn on the heater to use the spa, it works fine until it gets to about 95-degrees (I have it set to 99). Then it throws a High Limit 2 Fault, which turns the heater off, but only for about two minutes. Then the fault clears and the heater works normally the rest of the time. I had posted this problem a few months ago, and followed the suggestions to add insulation to the sensor heat shield. I did that about a month ago, but it had no affect. Last week I swapped out both sensors. Not only did that not fix the problem, the heater now turns off for about six minutes before resetting. I'm out of ideas.
RAYPAK Heater High Limit 2 Fault
- Thread starter hillyjd
- Start date
- Jul 21, 2013
- 65,068
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
From RayPak Heaters - Further Reading
Things you can try...
Things you can try...
- replace both high limit sensors and add thermal paste
- replace unitherm governor
- replace internal bypass
- add a heat shield
The sensor may be doing its job. The temperature reading on the heater is the inlet temperature of the water coming from the pool/spa. The high limit switches read the temperature of the water inside the manifold coming from the heat exchanger. It may be about 135 degrees, which is too hot, so the sensor trips (opens).
Check the internal bypass and the UniTherm governor as ajw22 suggested. Just replacing that safety device is like replacing an electrical breaker that is tripping without find out why it is tripping.
But why would the sensors reset after a couple of minutes and then operate normally as the water heats up another 5-10 degrees?
They are a simple thermal switch. They open when the temperature is too hot and close when it gets cooler. Heater shuts down, internal temp cools down, hi-limit closes allowing the heater to re-start. Why it takes another 5 - 10 degrees is unknown.
Assuming the unitherm governor is functioning as designed, the Raypak HL2 issue is extremely annoying to try and fix.
After I installed my heater back in 2022, it worked beautifully for about 6 months. After that, the HL2 fault problems started. Currently I have it working the best it's ever worked, and that was done by replacing the switch itself and using CPU/GPU thermal paste for a computer (Kryonaut Thermal Grizzly, to be exact), along with covering the metal bracket (shown in Allen's picture) in underhood self-adhesive thermal shield material. It will still trip an HL2 error now and then, but it's pretty rare these days.
After I installed my heater back in 2022, it worked beautifully for about 6 months. After that, the HL2 fault problems started. Currently I have it working the best it's ever worked, and that was done by replacing the switch itself and using CPU/GPU thermal paste for a computer (Kryonaut Thermal Grizzly, to be exact), along with covering the metal bracket (shown in Allen's picture) in underhood self-adhesive thermal shield material. It will still trip an HL2 error now and then, but it's pretty rare these days.
Since adding insolation and replacing the temp sensors only made things worse, the governor was next on the hit list. The more I thought about it, the more it makes sense that the governor is the culprit. Suppose it's just very slow to adapt to increasing water temp? As the temp rises, it's not allowing more flow through the manifold, so the water gets too hot in there and the sensor trips. But it's not broken completely; it's just slower than designed. So the heater turns off, and the governor finally gets to the correct setting so the there's enough flow to cool the water to within the sensor limits and everything is fine.
So this morning I replaced the governor. The old one had a lot of corrosion on the center (looked like crusty green lumps); that cannot be good. Put the new one in, fired up the spa and sat out there and watched. The spa heated from 70-degrees to 97-degees with no faults whatsoever. Victory!
So this morning I replaced the governor. The old one had a lot of corrosion on the center (looked like crusty green lumps); that cannot be good. Put the new one in, fired up the spa and sat out there and watched. The spa heated from 70-degrees to 97-degees with no faults whatsoever. Victory!
