Suburban Tankless Water Heater Cycling in warm temps

[CJAZ]

I have a year old rig with suburban st60 tankless water heater.



It has been cycling, preumably for the freeze protection but it's over 70 degrees outside. It tires to cycle often during the day though propane is off.


I was thinking it must be the input thermostat sensing the wrong temp, but not sure.



Any ideas?

 

[Lmdye]

Hi CJ, I have the same issue. I am surprised no one else has posted on your thread here. No the water heater should not be cycling - it has no water in it to protect from freezing. The water heater should only come on when you turn on the hot water faucet. I got mine to stop cycling by turning off the heater on the unit itself. Open the access hatch to the heater on the outside of the trailer and there is a on/off switch on the upper left corner. I left it off for 24 hours and then turned it back on the unit went back to normal. Now will it stay that way? Who knows. For now I am going to just leave it turned off at the unit until we take the trailer out again.

 

[CJAZ]

Hi CJ, I have the same issue. I am surprised no one else has posted on your thread here. No the water heater should not be cycling - it has no water in it to protect from freezing. The water heater should only come on when you turn on the hot water faucet. I got mine to stop cycling by turning off the heater on the unit itself. Open the access hatch to the heater on the outside of the trailer and there is a on/off switch on the upper left corner. I left it off for 24 hours and then turned it back on the unit went back to normal. Now will it stay that way? Who knows. For now I am going to just leave it turned off at the unit until we take the trailer out again.

Yes, I did the same. I'm not sure the heater knows if there's water in it or not, but it should know if it's at or below 40`ish or not. Mine was cycling up to 70+ F. Going to fire it up and test it out soon, like you I'm not sure if it's going to start cycling again or not. I think freeze protection is a good feature, but only if it works when appropriate.

I'm considering changing the temperature probes, they're the small brass nuts at the back of the water lines one on each side (in/out temps) with leads coming off the top. They're just threaded in with o ring seals, should be an easy swap but it's difficult to find reference values for the resistance based on temperatures. If you find something like that please pass it along.