26/08/2026
⚠️ A sauna can work perfectly after installation and still be wired incorrectly.
Smithtech Ltd recently attended a sauna in London after a 9 kW heater stopped working. The sauna had been operating for approximately two years since installation, so to the customer everything appeared to have been working correctly.
Our inspection found a different story.
The heater had been incorrectly connected for the available single-phase supply and was not wired in accordance with the manufacturer’s recommended arrangement. The full 9 kW heater load had effectively been passed through a single contactor within the control system.
It worked — but not for very long.
Eventually, the contactor failed, and we found visible evidence of overheating around its location inside the control box. The control system now requires replacement and the heater installation needs to be rewired correctly using the manufacturer-specified heat-resistant cable.
This is something we see far too often.
Connecting sauna heaters that have three separate heater outputs to a single-phase electrical supply can be confusing for installers who do not regularly work with sauna equipment. An incorrect connection does not necessarily cause an immediate failure. The sauna can heat up and appear to operate normally, sometimes for months or even years, while components are being subjected to loads they were not designed to carry.
Unfortunately, when the failure eventually happens, the customer pays the price.
In this case, work that should have been completed correctly during the original installation now has to be done for a second time, with the additional expense of replacing damaged control equipment.
Sauna installations involve more than simply providing power to a heater. Correct heater configuration, control equipment, temperature sensors, heat-resistant cabling and manufacturer-specific wiring requirements all need to be understood and followed.
Choosing the cheapest installation can become considerably more expensive in the long term.
Use an experienced sauna installer and get it done correctly the first time.
Smithtech Ltd – professional sauna inspection, fault finding, installation and commissioning.
