Thanks. My Raypak electric spa heater ELS 552-2 comes on regularly, but only heats the water (in a small indoor pool) to 88 degrees, then shuts off. The room temp is about 80, he pump flow is good and stop plate on the dial allows for maximum temperature. I'm wondering if the internal thermostat is improperly adjusted?? Please help Baffled in Boston..

Check the temperature sensor for resistance (ohms).
Temperature
(deg. F) 61 68 70 77 86 88 95 104 106
(k ohms) 14.92 12.49 11.88 10.00 8.06 7.69 6.53 5.33 5.10

If your ohms are below about 7K the heater thinks the water is hotter than it actually is, so it shuts down. It's a fairly common repair.

If you do not keep close watch on your water chemistry, depending on your location , you could have a large calcium build-up or salt build up on your electric heating element. Also, these models are meant for spas, and depending on the weather in your location, the heater might have trouble keeping up.

Mechanical thermostats such as the one in your heater are only accurate between 3-5 degrees once set. Unlike a digital thermostat that is accurate to .1 degrees. You can purchase an aftermarket thermostat for $120 that is digital and can be installed in your heater.

You have a spring loaded valve inside the water manifold. Open the manifold and make sure that that valve is closing. Then or first make sure if you have a by-pass valve be sure that is almost closed.these will make sure that the water is going through the heater. Also remember you shouldn't be able to feel any hot water at the returns. That is part of what these valves do. They help keep anyone from getting scolded by too hot water. The water at the return should be no more than 7 to 10 degrees hotter than when it goes into the heater.

where the thermostat is located, the pump is not circulating the water

that water leak would not keep the heater from coming on is there power to the heater check and see if it is on there is a switch on and off switch on the side of the heater, check and see if it is on