ST1301 Generic Solar Hot Water Thermostat 50-70C SPST Surface Mount with Single Shot OTC, Alternative to ST1301133 ST13-70K

For solar hot water systems with an electric booster, ST1301 is a generic surface mount thermostat that adjusts from 50 to 70C. It's a single pole, single throw (SPST) design with a single shot over-temperature cut-out (OTC) built in. It follows the ST1301133 (ST13-70K) style, so compare the body, mounting and terminals with your existing thermostat before ordering.

Solar booster not heating? Checking the thermostat

On a solar system, the electric booster element tops up the heat on cloudy days or when demand is high, and this thermostat decides when it runs. It senses the tank temperature through the wall it's clamped against and switches the element off once the set point is reached. If it fails, the booster may never come on, leaving lukewarm water in poor weather, or it may let the water overheat. The OTC cuts the element if the water gets dangerously hot, and a tripped OTC always needs investigating.

Part details

• Part number ST1301, generic replacement thermostat
• Adjustable 50 to 70C
• SPST switching
• Single shot over-temperature cut-out (OTC)
• Surface mount, made for solar hot water systems
• Follows the ST1301133 (ST13-70K) style

Thermostat replacement is a job for an electrician

Hot water thermostats are hard-wired, so the work must be done by a licensed electrician. The circuit has to be isolated at the switchboard and tested dead before the cover comes off. Note how the old unit is wired and positioned, seat the new one firmly against the tank, set it to at least 60C, and confirm the booster cycles correctly once power is restored.

Questions about this part

Can ST1301 replace my ST1301133 thermostat?

It's a generic alternative in the same style, with a 50 to 70C range and SPST switching. It isn't a Robertshaw branded part. Have your electrician compare the mounting and terminals with the old unit before fitting.