Pressure Switch | Swim Spa

The 4035P Pressure Switch is the heater flow-sensing switch for Arctic Spas swim spas — plastic body, 1/8" MPT connection, calibrated for the flow characteristics of swim spa plumbing. It confirms water is moving through the heater before the controller allows heating; when it can't, the topside throws an FLC ("flow check") code and locks the heater out.

When you'll need to replace it: an FLC error that survives a filter clean and a pump check usually means the switch — corroded contacts, a tired diaphragm, or cracked threads. It's the cheapest link in the heating chain, so swap it before blaming the heater.

Will this fit my spa? Yes, on Arctic Spas swim spas. Regular hot tubs take the 4163P-EW switch (current models) or the Model 3902 (older models).

How to install: drain below the heater, swap the switch at its 1/8" MPT port with fresh Teflon tape, hand-tighten, reconnect the spade terminals, refill and confirm the code clears.