Filling and draining a hot tub is a commissioning task, not just hose work. During a fill you are proving that drains and unions seal, air can leave the circulation system and every heater receives the water level and flow it requires. During a drain you are controlling a large volume of warm, treated water while preventing pumps, pipes and the foundation from being left in a damaging state.
Before the hose goes into the tub
Read the final configuration, because a simple wooden soaking tub, a pumped massage system and an external wood-stove circuit do not fill in exactly the same way. Confirm the drain and service plugs are fitted, unions are seated and valves are in the specified fill position. Clean the vessel with products suitable for its real wet-side material.
Keep electrical equipment isolated until the instructions call for it. A pump must not start dry. A water-carrying wood heater must be cold and unlit until the tub reaches its stated operating level and the complete circuit is open and vented. Make sure the hose itself is clean; a hose stored with stagnant water can contaminate a freshly cleaned tub.
Fill slowly enough to commission the connections
- Start at low flow. Watch the drain, lights, jets, heater ports and visible unions as the level passes each penetration.
- Stop for a real leak. A stream beside a fitting needs correction; it should not be dismissed as normal swelling of a solid-wood vessel.
- Fill to the model’s mark. “Above the highest jet” is not universal. Suctions, skimmers, heaters and seating displacement determine the specified band.
- Vent and prime. Follow the pump/filter procedure so trapped air can escape. Do not let a pump continue humming without steady return flow.
- Complete the cold commissioning checks. Inspect accessible connections for leaks and verify pump operation where fitted. Do not expect a cold passive thermosiphon to behave like a running pump, and do not improvise a pressure test.
- Test and treat the actual water. Record the source and initial readings, then follow the selected water-care system for the real volume.
If the pump hums but water does not return
Switch it off. Repeated dry running can damage a pump. Recheck the water level, filter seating, service valves and the model’s priming point. A trapped air pocket after a refill may require the documented venting procedure; loosening random unions around live equipment is not a safe substitute. If the pump will not prime or trips protection, keep it isolated and obtain service advice.
Plan the complete drain volume before opening a valve
Choose a permitted destination for the complete volume before opening the drain. Keep the flow away from the base, buildings, neighbouring land and unsafe walking routes. A hose placed on a lawn does not establish that water will soak in without reaching a drain or watercourse.
Requirements differ by UK nation, discharge route and domestic or business use. Ask the relevant environmental regulator and sewerage provider where permission or treatment conditions are needed; confirm cooling and residual disinfectant requirements for that route. Do not assume a septic tank or surface-water drain can receive the water.
SEPA’s Scottish hot-tub discharge guidance separates the rule for one hot tub discharging to groundwater from registration and permit activities. Check which route applies to the property. This is Scottish guidance, not UK-wide permission.
Drain, clean and leave the system in a defined state
Use the built-in drain or a suitable pump as permitted, without leaving electrical connections in standing water. When flow stops, open only the drain points identified in the manual. Clean the wet-side surfaces and inspect the waterline, suctions, seals and accessible pipework. Record any debris or corrosion before it is removed.
If the tub will be refilled immediately, protect clean components and repeat the leak/prime check. If it will stand empty, follow the material’s storage rules. A traditional solid-wood vessel can dry and shrink; a lined tub has different requirements.
Draining for winter is a separate job
An apparently empty tub can retain water in pump housings, filters, heaters, jet bodies and sagging hoses. If the system is being winterised, each documented low point must be drained or cleared using the approved method. Do not use automotive antifreeze. A wet/dry vacuum is appropriate only where the manufacturer specifies how and where it may be connected.
If the tub will remain operating, do not partially drain it as a precaution. Use the verified winter heating, circulation, cover and monitoring routine described in the winter hot tub guide.
Keep a short fill-and-drain record
For the first fill, keep the configured model and heater manual beside the commissioning record. This captures the useful checks before heat or finishes conceal a problem.
| Stage | Evidence to record |
|---|---|
| Before filling | Date, model/serial, manual revision, completed base and electrical sign-off where required |
| During the fill | Water source, measured volume where available, required level and locations checked for leaks |
| Before heat | Open-path and venting checks from the exact drawing; pump/flow result where fitted |
| Handover | Responsible person, control demonstration, faults and whether the system was cleared for use |
| Before draining | Reason, water condition, authorised route and safe cold shutdown |
| After emptying | Refill, material-specific storage or complete winterisation state |
A drop below a union, an unexplained water-level fall or failure to establish required pump flow must be resolved before heating. Record the location and contact the supplier rather than tightening fittings or bands by guesswork. For the subsequent return to use, follow the recommissioning checks.
