Hot tub not heating?
Start here.

First, which kind of not-heating is it?

These sound the same on the phone and they are different problems. Knowing which one you have narrows the list before anyone gets in a truck.

• Stone cold. No heat at all, water at roughly ambient temperature. Points at the heater, a sensor, or the pack.
• Warm but never gets there. Climbs, stalls a few degrees short, or drifts down overnight. Points at flow, a cover that has stopped insulating, or a heater working at reduced output.
• Heats, then quits. Reaches temperature and cuts out, sometimes with a code. Very often a high limit tripping on restricted flow — see HL and HFL .

The two things to check before you call

• The filter. This is not filler advice. A packed filter is the most common single cause of a heating complaint, because the heater needs flow and a blocked filter starves it. Pull the filter out entirely and run the tub for an hour. If it starts heating, you have found it and saved yourself a service call.
• Water level. Below the skimmer intake, the pump pulls air and flow collapses. Top it to the middle of the skimmer opening.

If either of those fixes it, the underlying lesson is worth taking: filters and water care are the cheap end of a chain that ends in heaters and pump seals. That is what scheduled maintenance and water care is for.

The five real causes

• Restricted flow. Filter, level, valves, air lock. Usually shows as FLO or FL1 or a tripping high limit.
• A failed heater element. The single most common part we replace. Elements do not last forever and they have no moving parts to warn you.
• A failed sensor. The board cannot measure the water so it will not heat it. Shows as SN1 or SN3 .
• A tripped high limit. The safety cut-out doing its job, usually because of flow. See HL .
• A control pack fault. Least common, most expensive, and the one worth confirming with a meter before anybody buys anything.

What a diagnosis actually involves

Continuity and resistance at the element, sensor readings against real water temperature, flow through the heater, and what the pack is actually commanding. That is a measurement job and it is why we charge for the diagnosis rather than guessing: the difference between a $40 sensor and a heater is found with a meter, not a hunch.

The $185 covers the trip and the diagnosis. You hear the fault and the cost before anything is replaced, and if a part has to be ordered you know that on day one along with the timeline. We stock the majority of common parts and we service all makes and models, including brands whose dealers are long gone.

Where we stop

Electrical work on a spa circuit is licensed work in Michigan and Dr. Spa does not do it. If your tub is not heating and tripping its breaker, read the breaker page first — that is a different fault and it comes with a safety rule attached.

Related codes

FLO , HL , DR and SN1 all end up here eventually. The full error code index covers all twelve.