OH on a hot tub:
it overheated.

What OH means

OH — OHH on some control packs — means the water temperature measured at the heater has gone past the safe ceiling the manufacturer set, commonly somewhere around 110 to 112 degrees. The board kills the heater and posts the code. It is the tub protecting itself and you.

Do this first

• Take the cover off. A closed cover on a well-insulated tub is the single biggest reason the water cannot shed heat.
• Do not get in. Not until it has cooled and you know why it happened.
• Let it drop, then watch it. Most packs clear the code themselves once the temperature comes back into range.
• If it comes straight back, stop resetting it and call. A tub that overheats repeatedly is telling you about a fault, not having a bad day.

Why it got hot in the first place

This is the part people skip, and it is the part that decides whether it happens again next week.

• Pump heat. Jet pumps put real energy into the water. Long sessions, or a pump stuck running on a timer or a jammed relay, will lift the temperature well past the set point with no heater involved at all.
• A temperature sensor reading high. The water is fine, the sensor is lying, and the board is acting correctly on bad information. Related codes are SN1 and SN3 .
• Restricted flow. Water moving too slowly through the heater gets much hotter at the element than the shell temperature suggests. If you have also seen FLO or FL1 , that is the likely story.
• A stuck heater relay. The heater is being told to stop and is not stopping. Less common and more urgent than the others.

What we do about it

The diagnosis is a measurement job, not a guess: sensor readings against actual water temperature, flow through the heater, pump behaviour and relay state. The $185 service call covers the trip and the diagnosis, and you hear the fault and the price before any part is ordered. Dr. Spa has worked on all makes and models since 2001, which includes plenty of packs whose manufacturers are long gone.

Where we stop

Electrical work on a spa circuit is licensed work in Michigan and we do not do it. We diagnose everything on the spa side of the disconnect. Anything hot, scorched, melted or smelling of burning gets the breaker turned off first and a call second, and that goes double for a tub that has been running hot.

Related codes

HL and HFL , SN1 and SN3 and COOL and COL all sit near this one. The full error code index covers all twelve.