Draining a pool heater for winter requires removing drain plugs from the heat exchanger header (the horizontal pipe at the base of the unit where pool water enters and exits) after shutting off gas supply, turning off the circuit breaker, and allowing the unit to cool for 15-20 minutes. Most gas heaters have 1-2 drain plugs on the front inlet-outlet header, with some models having a second plug on the rear return header accessible through side panel removal. Heat pump heaters require disconnecting water piping, removing the condenser drain plug, and blowing air through the heat exchanger with an air compressor to ensure complete drainage. Freeze damage to heat exchanger tubes costs €600-2,000 in repair or full unit replacement and is excluded from all manufacturer warranties.
This guide covers pre-drainage safety steps, drain plug locations for major brands (Hayward, Pentair, Raypak/Rheem, Jandy/Zodiac), brass versus plastic drain cock differences, heat pump heater drainage procedure, pressure relief valve operation, post-drainage vent protection, spring reinstallation, and natural pool considerations where heaters are typically absent.
Key Takeaways
- Gas and power off before starting – gas valve closed, circuit breaker off, verify no power
- 15-20 minute cool-down required – hot heat exchanger damaged by rapid cold water contact
- Drain plugs on inlet-outlet header – horizontal pipe at base where water enters/exits
- Some models have rear header plug – requires side panel removal for access
- Brass drain cocks: reinstall after winter – leaving out causes thread rust making spring seal difficult
- Plastic plugs: leave out all winter – safe to store in pump basket until spring
- Heat pump: blow out with air compressor – passive drainage alone insufficient, water remains in passages
- Cover exhaust vents – wire mesh prevents rodent nesting in heater interior
Why Draining the Heater Matters
Water expands approximately 9% on freezing. Heat exchanger tubes inside pool heaters are copper or cupronickel (copper-nickel alloy). They have a precise diameter, and are thin-walled for efficient heat transfer. Any water remaining in these tubes freezes, expands, and splits the tube wall. Replacement heat exchanger cost €400-1,500 (part only), with labour adding €200-500. Full unit replacement €1,500-4,000.
Freeze damage to pool heaters is explicitly excluded from all manufacturer warranties and companies like Raypak, Hayward, Pentair, or Jandy each state this clearly. Proper seasonal drainage is the owner’s responsibility.
Portugal context: Coastal areas (Algarve, Lisbon, Porto) rarely reach sustained freezing which means that heater drainage is optional during most years. Interior regions (Serra da Estrela, Alto Trás-os-Montes, Alentejo highlands) experience sustained winter freezing requiring full drainage procedure.
Safety Steps Before Starting
Step 1: Shut Off Gas Supply
Turn off gas isolation valve on incoming gas line to heater (typically ball valve on gas pipe adjacent to heater). The valve is closed when handled perpendicular to the pipe.
For heaters connected to LPG (propane) bottles, close the bottle valve fully.
Triple check gas is off and do not proceed until you can confirm it is closed.
Step 2: Turn Off Electrical Power
Switch off circuit breaker serving pool heater at consumer unit. For combined pool equipment circuits, identify the correct breaker by label or test.
Some heat pump heaters have a dedicated 3-phase supply. Ensure all phases are isolated at the breaker.
Verify no power: Attempt to start heater at controller and confirm zero response.
Step 3: Allow Cool-Down Period
15-20 minutes minimum after last heater operation before removing drain plugs.
Reason: Heat exchanger internal temperature reaches 50-80°C during operation. Removing drain plugs immediately allows residual hot water to flash-drain from hot metal – rapid temperature differential causes thermal stress micro-cracking in heat exchanger joints. Allowing cool-down prevents this.
Hot water warning: Water exiting drain plugs on recently operated heaters may still be hot (40-60°C) even after a cool-down period. Position clear of body when removing plugs.
Step 4: Close Isolation Valves
Close valves between heater and pool system to prevent pool water backfilling heater during drainage. If no isolation valves, ensure the pump is off (confirmed by circuit breaker) before proceeding.
Drain Plug Locations by Brand
Hayward H-Series (Natural Gas and Propane)
Front header plugs: Two drain plugs on inlet and outlet connections at base of unit on front panel. Plugs are plastic, typically 19 mm, removed by hand or large flat-head screwdriver.
Accessing plugs: Open front service panel (two screws, top and bottom). Plugs visible at base of unit on left and right sides of water connection header.
Union disconnection: Hayward recommends also disconnecting plumbing unions and tilting the heater toward the plumbing side. It removes additional residual water from union bodies and heater ports that gravity drainage misses.
Pressure switch: Some H-Series models have a pressure switch with water in the sensing line. Disconnect sensing line at pressure switch to drain residual water from this component.
Plastic plugs only on Hayward – store in pump basket over winter, reinstall at spring start-up.
Pentair MasterTemp and Sta-Rite Max-E-Therm
Front header plug: Single plug on front inlet-outlet header (combined header design). Located at the lowest point of the header.
Rear drain (older models): Some MasterTemp models have a second drain at the rear header that can be accessed by removing the left or right side cabinet panel. Consult model-specific manuals.
Union connections: Disconnect inlet and outlet unions (hand tighten originally – unscrew by hand). Tilt unit slightly forward. This directs residual water toward the front drain opening.
Plastic plugs – leave out over winter, stored in pump baskets.
Raypak (Including Rheem Pool Heaters)
Front header plug: Single drain plug on front inlet-outlet header at base. Access without panel removal on most models.
Rear header plug: Remove cabinet panels on side opposite water piping to access drain plug on return header. Both front and rear plugs should be removed for complete drainage.
ProTek Shield module (newer Raypak models): Unscrew entire ProTek Shield module from front header – provides drainage point and the module itself should be stored indoors (contains electronic components).
Union disconnection recommended: Raypak documentation recommends disconnecting plumbing unions where possible and tipping heater toward plumbing to drain union bodies and internal passages completely.
Blow-through: After removing plugs and disconnecting unions, Raypak recommends blowing air through the heater using an air compressor inserted at one union connection. It pushes residual water from heat exchanger tubes.
Plastic plugs – leave out over winter.
Jandy/Zodiac LXi and JXi
Brass drain cocks: Jandy heaters use brass drain cocks (small quarter-turn valves) rather than threaded plugs. Located on the header at the base of the unit.
Critical difference with brass plugs: Unlike plastic plugs left out over winter, brass drain cocks must be reinstalled after winter drainage. Leaving brass drain cocks out exposes heater case threads to outdoor conditions – different metals (brass cock, aluminium or stainless case) cause galvanic corrosion seizing threads. Spring reinstallation becomes extremely difficult or impossible if threads corrode.
Removal tool: 9/16 inch wrench (not adjustable/shifting spanner – fine brass threads strip easily with incorrect tool). Turn slowly, do not force.
Reinstall after drainage: Open fully to drain, leave open 5-10 minutes, then reinstall lightly – threads must remain protected.
Access: Front panel removal required for some JXi models – two screws, lift off.
Heat Pump Pool Heaters (Zodiac, Madimack, Aquacal, Generic Inverter Units)
Heat pump heaters differ significantly from gas heaters. They use refrigerant circuits to extract heat from air rather than combustion. Different drainage procedures.
Leave in place: Do not move the heat pump for winter. Vibration during transport damages refrigerant circuit components. The heat pump enclosure withstands all weather conditions.
Water circuit drainage:
- Turn off circuit breaker (mandatory as heat pump electrical components are at risk if water is present during power cycling)
- Disconnect water inlet pipe at heater connection point
- Remove condenser drain plug (located at lowest point of titanium heat exchanger, consult model documentation for location)
- Water drains from heat exchanger
Blow-out essential: Passive drainage alone leaves water in heat exchanger passages. Connect the air compressor to the water inlet connection after the plug is removed. Blow air through at 10-15 PSI, so water exits from the drain plug opening an outlet pipe. Continue until only air exits. Reconnect pipes after blowing.
Fan and coil protection: Inspect refrigerant coil (external fin array) for debris such as leaves, insects, or dirt and reduce efficiency. Clean with a low pressure garden hose. Do not use a pressure washer on the coil as it bends aluminium fins.
Pressure Relief Valve
Many gas pool heaters have a pressure relief valve (PRV) on the heat exchanger. It’s an automatic safety valve that opens if internal pressure exceeds rated limit.
Location: Top of heat exchanger section or on outlet header. Has a lever or small handle for manual opening.
Winter procedure: Open PRV manually by lifting the lever for 5-10 seconds. It allows residual pressurised water to escape before plug removal equalises pressure inside the heater.
PRV maintenance: If the PRV lever is stiff, corroded, or does not seal properly after testing (water continues dripping after closing), replace before next season. PRV is a safety component, but non-functional PRV is a hazard risk.
Post-Drainage Steps
Vent Protection
Cover combustion air intake and exhaust vents (typically located on heater top or rear, depending on unit) with wire mesh or aluminium flyscreen material secured with cable ties.
Reason: Open vents during the 3-5 month winter period allow rodents (mice, rats) to nest inside the heater cabinet. Nesting material on combustion components creates fire hazard at spring start-up. Rodents also chew electrical wiring, gas supply tubing, and rubber components.
Cover type: Wire mesh only allows air circulation preventing condensation buildup inside the cabinet, while excluding rodents. Do not use solid covers (plastic sheeting, tarpaulin) over the entire heater as it traps moisture and can cause corrosion.
Cabinet Panel Condition
Check cabinet panels are correctly reinstalled and screws secure. Loose panels allow wind to enter cabinets, increase internal moisture, and reduce structural protection for components.
For heaters in exposed coastal locations (salt air), inspect cabinet panels for corrosion. Light surface rust on painted steel panels treated with rust converter and touch-up paint. Perforated or heavily corroded panels should be replaced before next season.
Documentation
Note drain plug locations (front, rear, PRV position) in a maintenance log or photograph with phone before reassembling. Makes next season’s winterisation faster and ensures no plug location is missed.
Spring Reinstallation
Drain Plug Reinstallation
Plastic plugs: Clean thread, inspect o-ring or thread tape condition, apply fresh thread tape (PTFE tape, 2-3 wraps) or ensure rubber washer in good condition. Thread hand tight plus quarter turn with appropriate tool. Do not overtighten as it can crack plastic plugs.
Brass drain cocks: Thread slowly by hand into heater body ensuring thread alignment (cross-threading strips brass immediately). Once hand tight, use a 9/16 wrench for quarter turn – no more. Check for drips on first water contact.
ProTek Shield module (Raypak): Reinstall module, ensure o-ring seated correctly in groove, thread collar clockwise until seated, then hand tight. Check for leaks at start-up.
Spring Start-Up Procedure
- Reinstall all drain plugs
- Reconnect unions (hand tight, check for leaks)
- Open isolation valves restoring water to heater circuit
- Restore gas supply (open isolation valve slowly)
- Turn on circuit breaker
- Start pool circulation pump and allow water to flow through heater 2-3 minutes before starting heater (purges air from heat exchanger)
- Check for water leaks at all drain plug locations and unions
- Start heater following manufacturer ignition procedure
- Check for gas smell and if there’ any gas odour, shut it down immediately and contact a gas engineer
Natural Pool Considerations
Natural swimming pools in Portugal’s Mediterranean climate rarely use heaters – the primary reason heater winter drainage arises in conventional pool ownership.
Why natural pools typically forgo heating: Mediterranean water temperatures (18-25°C May-October at coastal locations) provide a comfortable swimming season without supplemental heating. Natural pool biological filtration functions best at ambient temperatures – artificial heating of water above 28°C accelerates algae growth, disrupts bacterial balance in regeneration zones, and increases evaporation from planted areas.
If a heater is installed: Natural pool heaters drain using identical procedure to conventional pools. The heater type determines drain procedures, not the pool filtration method.
Simplified winter closure: Absence of heater removes the most technically complex single component from natural pool winterisation procedure. Closure reduces to pump and filter drainage, line blowing, and cover installation.
Oásis Biosistema designs natural swimming pools that operate year-round in Portugal’s climate without heaters, using biological filtration through planted regeneration zones to maintain water quality across seasons while eliminating heater installation, drainage, and maintenance requirements from the owner’s annual maintenance cycle.
Conclusion
Draining a pool heater for winter requires shutting off gas supply and circuit breaker, waiting 15-20 minutes for cool-down, then removing drain plugs from the front inlet-outlet header (all major brands) and rear return header where accessible (Raypak, some Pentair), with Jandy brass drain cocks requiring reinsertion after drainage to protect threads while plastic plugs from Hayward, Pentair, and Raypak are left out stored in the pump basket. Heat pump heaters require disconnecting water inlet piping, removing the condenser drain plug, and blowing through with air compressor at 10-15 PSI since passive drainage alone leaves water in heat exchanger passages.
Natural swimming pools designed by Oásis Biosistema eliminate heater drainage from winter procedures entirely as biological filtration through planted regeneration zones maintains water quality across Portugal’s mild Mediterranean seasons without supplemental heating, removing the most technically complex component of conventional pool winterisation.
FAQ
How to get water out of a pool heater for winter?
Turn off power and gas to the heater, then remove the drain plugs and open any drain valves. Allow all water to flow out completely. Some owners also use compressed air to clear remaining water from the heat exchanger and plumbing lines.
Where is the drain plug on my pool heater?
The drain plug is usually located near the bottom of the heater manifold or water header. The exact location varies by manufacturer and model, so check your owner’s manual if you cannot find it easily.
How to winterize a pool heater?
To winterize a pool heater, shut off power and fuel, drain all water, remove drain plugs, and clear plumbing lines. Leave the plugs out during winter so any remaining moisture can escape and won’t freeze inside the unit.
How to drain a pool pump for winter?
Turn off the pump power, remove the pump basket lid, and unscrew the drain plugs near the bottom of the pump housing. Let all water drain completely, then store the plugs safely until spring opening. This helps prevent freeze damage to the pump.
