The Pacific Northwest heat domes — extreme temperature events where temperatures reach 100°F+ in the Eastside for multiple consecutive days — create hot tub problems that the region's usually mild climate rarely generates. The 2021 heat dome was a stark reminder that Eastside spa systems are designed for a marine climate, not a desert one.
Most spa control systems have a maximum water temperature limit of 104°F. During a heat dome event, a spa sitting in direct afternoon sun can absorb enough solar heat to push water temperature above this limit without the heater ever running — tripping the high-temperature protection and shutting the spa down. This is the system working correctly. The OH or high-temp error code will clear once the spa cools below the reset threshold.
To use your spa during a heat dome: shade it during peak afternoon hours (2–6pm), run the jets to circulate and allow some evaporative cooling, and lower the thermostat setting. Operating at 98–100°F rather than 104°F during extreme heat keeps the spa functional without constantly tripping the high-temperature protection.
Eastside spa equipment is rated for moderate operating temperatures. During a heat dome with ambient temperatures at 100°F+, the equipment bay — particularly on spas with enclosed, dark-colored cabinets — can reach temperatures well above the rated range for pump motor insulation, capacitors, and circuit board components. Eastside spa owners who experience equipment failures within weeks of a major heat dome event should consider heat exposure as a contributing factor.
Opening the equipment bay door during extreme heat events allows hot air to escape and reduces the internal temperature significantly. This is one of the simplest steps to protect equipment during heat domes.
Heat accelerates chemical reactions in spa water. Sanitizer demand increases in hot water — free chlorine or bromine depletes faster at 90°F water temperature than at 100°F set-point temperature. Evaporation increases dramatically, concentrating minerals and chemicals. Check chemistry daily during heat dome events rather than weekly. Expect to add sanitizer more frequently and to see pH rise faster than usual as CO2 off-gasses from the hot water surface.
If your spa experienced failures during or immediately after a heat dome event, call Cascade Spa Repair for diagnosis. We service Kirkland, Bellevue, Redmond, Sammamish, and the full Eastside. Fixed quote after diagnosis. Call (425) 832-8476.
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