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How to Winterize a Pool Heater

Drain a pool heater before it freezes. Hayward and Pentair shut-down and drain steps for gas heaters and heat pumps, plus a safe spring restart.

October 15, 2026•PoolSpaKit Editorial
Gas pool heater and heat pump shut down on the equipment pad for winter

To winterize a pool heater, shut it down and drain all the water out of it using the winterizing steps in its manual, because water left inside can cause freeze damage that the warranty doesn’t cover. Hayward’s rule is that in regions where freezing temperatures are encountered, all water must be drained from the heater when it is out of service. Pentair says to winterize once air temperatures are expected to drop below freezing (32° F/0° C).

The shutdown is different for a gas heater and a heat pump, so use the section for yours. The steps below are the owner-level parts of the manuals: switching off, closing valves and opening drains. Leave anything involving gas lines, burners, refrigerant or removing components to a heater technician.

Don’t use the heater as freeze protection

Hayward is direct about this: do not use the heater to maintain the water temperature just above freezing or for freeze protection. If you run it in freezing weather, the pump must run continuously. A pool that stays open in winter needs a circulation plan instead; see pool freeze protection.

Freeze damage is on you: a heater damaged by freezing is not covered under the Hayward warranty, and Pentair says allowing the heater to freeze voids the warranty.

If the heater sits below the pool’s water level

Opening the drain on a heater that sits lower than the pool will drain the pool through it. Pentair says: if heater is below pool water level, be sure to close isolation valves to prevent draining the pool. Hayward says that to drain a pool heater located below the pool water level, you must either partially drain the pool or isolate the heater with valves. If your plumbing has no isolation valves, ask the installer how your system was designed to be drained.

Gas heaters

Hayward Universal H-Series

  1. Set the heater to STANDBY mode using the keypad.
  2. Turn the electricity to the heater OFF at the circuit breaker panel.
  3. Turn the heater gas valve OFF using the knob or switch on the valve.
  4. Turn the heater’s gas supply OFF at the main shut-off valve outside the heater cabinet.
  5. Be sure the circulating pump is OFF.
  6. On models with plastic headers, remove the plastic drain plug. On bronze-header (ASME) models, open the brass drain valve on the header.
  7. Let all the water drain out, then refit the plug or close the valve.

Pentair MasterTemp

  1. Turn off electrical supply to the heater and pump.
  2. Close main gas control valve and manual gas valve (located outside the heater). Turn switch on heater gas valve to OFF.
  3. Where the manual calls for it in northern climates, open drain cock located on the bottom of the manifold adapter, and drain the heat exchanger and manifold adapter completely.
  4. Cover air inlet grate with a plastic bag to prevent bugs, leaves, etc., from getting into the heater.

Draining by gravity can leave some water in the heat exchanger; Pentair’s air-assisted step is one for your technician. Pentair’s full procedure has more steps: it has you remove the water pressure switch, plug its port, and if needed install a drain cock in the outlet pipe. It also allows air to help the draining, with a warning: purging the system with compressed air can cause components to explode, so only a low pressure (below 5 PSI or 35 kPa), high volume blower may be used. Those steps involve parts and tools most owners don’t have; book them with your service visit.

Heat pumps (Hayward HeatPro)

  1. Set the heater to STANDBY mode using the keypad.
  2. Turn the electricity to the heater OFF at the circuit breaker panel, and make sure the circulating pump is off.
  3. Drain it. If no drain plug is provided, open lower inlet water union and allow all water to drain from the heater.
  4. Re-install the drain plug or reattach the water union.

The unions matter: Hayward says the supplied union connectors must be installed on the heat pump water inlet and outlet so the unit can be serviced and winterized. If yours was plumbed without them, draining it is a job for the installer. As with gas units, a heat pump damaged by freezing is not covered by Hayward’s warranty. Heat-pump basics are in pool heater types.

Starting it again in spring

Close the drains and refit plugs first. Pentair says: if the heater has been drained for freezing condition, do NOT turn “ON” until the system is circulating water, and to let water circulate for several minutes until air noises stop. Hayward heads its gas-heater spring start-up section “consult a professional”, which is sensible for a gas appliance that has sat for months. If it won’t fire afterwards, see pool heater not heating.

The pump and filter are drained separately; the rest of the closing is in our above-ground winterizing checklist and the pool equipment and circulation guide.

Sources

Research checked 2026-10-14.

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