I've got a 7 year old Leisure Bay spa that is giving me an OH (overheat) problem. The problem only occurs when I put it in stand-by mode or if the power goes out temporarily. It would seem that the water continues to heat up while the circulation is off and it trips an OH. Could this be caused by excessive calcium build-up in the heater? If not, what else could be the culprit?

Any help on this?

Hi NC-Spa,

With the previous posts pointing to the Baqua Spa usage in your spa, I would bet that you are calcium scaled. If you have mystery chips or flakes of white slightly curved particles collecting in the footwell of the spa, you are scaled. The calcium is cooking onto your element, (and Grundfos pump) and as the flow stops, continues to conduct residual heat. You also need to make sure that the "Two Port Return Jet" is not collecting calcium chips, and clogging out. I find that seriously scaled out elements have the buildup close to the high limit probe keeper, and exhibit the same symptoms. You can also listen to the 3" vertical heater for the "hissing" of scale baking. If this is the case, you will need to replace the heater. Expect to do the same for the Grundfos soon.

Hope this helped

Thanks inhotwater. That is what I suspected. I used to add calcium to get up to the water hardness level indicated on the Baqua Spa test strips, but I no longer do. My understanding is that the hardness level is only to reduce foaming, and I don't have a foaming problem. Our water is pretty hard to start with. The Grundfos has already been replaced and I keep an eye on the "two port return jet" to make sure I get good flow. I guess I'll be replacing the heater soon.