What does a technician check when a pool heater won't fire?

When a gas pool heater will not fire, a technician works through a fixed order: is the heater being told to run, is water moving through it, is it getting power, and then does it light. Most no-heat calls end at one of the early questions, such as a pump that has lost its prime, a dirty filter or a water pressure switch that is not closing. The later questions involve gas and live wiring, which is why a licensed pro does them.

What you can rule out first

Raypak's owner instructions for a gas pool heater that will not fire start with the basics. If there is no power, the circuit breaker may have tripped.^[1] If there is power, they say the time clock must be in the "ON" position, the pump strainer basket may be full, the filter may be dirty and the pump may have lost its prime and be running dry.^[1] A higher-than-usual reading on the filter pressure gauge points to a dirty filter, and no pressure at all means water is not moving.^[1]

Those are ordinary pool-care items, and telling the technician which of them apply saves time on the clock. Everything past them is for a licensed pro.

What the technician checks, in order

Water flow and the pressure switch. Gas pool heaters will not light without water moving through them. Raypak says its water pressure switch shuts off the burners if the water supply is interrupted, and that it is very important to verify that the switch electrically opens and shuts off the gas valve when flow is interrupted.^[1] The switch is factory-set at 1.75 PSI for deck-level installations, and when the heater sits below the level of the pool it may need adjusting to compensate for the static head.^[1] On a digital heater the display shows "Water Sw Open" when the pressure switch is open while the heater is calling for heat.^[1] A technician confirms the filter is clean and the pump is moving water before blaming the switch.

Safety limits. The same status list shows other open circuits that stop a heater, including a vent spill switch, a rollout switch, a high limit and a field-supplied flow switch.^[1] Each one is a safety device, and the technician finds out why it opened rather than bypassing it.

Power and the control board. Raypak's digital troubleshooting flow chart starts with checking line voltage power, the low voltage transformer, the limit controller, the thermostat and the wiring, and asks whether the PC board has 24 volts nominal.^[1] Raypak adds that the line voltage must not be 208 VAC.^[1]

Spark and ignition. The chart then asks whether there is spark across the igniter and sensor gap. If not, it points to the ignition cable, ground wiring, ceramic insulator and gap, and to signs of melting on the cable boot.^[1] A failed attempt shows on the display as an ignition fault. In one case Raypak says the heater will lock out for 60 minutes before retrying after the pilot flame was lost four times within the trial to ignite the main burner.^[1] So a heater that was dead at 3 p.m. may try again by itself an hour later, and the technician reads the fault history rather than judging by what the heater is doing now.

Gas supply and the pilot. If the pilot or main burner does not light, the chart sends the technician to check that all manual gas valves are open, that the supply tubing and pressures are good and that the pilot burner orifice is not blocked.^[1] On a millivolt model, a pilot output below 500 mV means checking gas pressure and looking for insects or debris in the pilot burner.^[1]

Thermostat, limits and gas valve. On millivolt models the chart works through jumping across the pressure switch, the thermostat and each high limit one at a time to find the part that is holding the heater off. The parts it names for replacement include the pressure switch, thermostat, high limit, pilot generator, PC board and gas valve.^[1] Jumpers on live controls are not something to try at home.

Why it is a licensed-pro job

Raypak's manual says installation and service must be performed by a qualified installer, service agency or the gas supplier.^[1] It adds that service personnel may be required by some states to be licensed.^[1] If you smell gas, the manual says not to try to light any appliance, not to touch any electrical switch or use a phone in your building, and to call your gas supplier from a neighbor's phone, or the fire department if you cannot reach the supplier.^[1]

When to call a licensed pro

For anything beyond the pool-care checks above. Virginia has licence rules for gas work: no individual may engage in work as a liquefied petroleum gas fitter or natural gas fitter provider unless licensed under the same article of the Code.^[4] The definition of a liquefied petroleum gas fitter excludes hot water heaters, boilers and central heating systems, which require a heating, ventilation and air conditioning or plumbing certification.^[3] Ask the business which DPOR licence it holds for your heater. DPOR also says that if the work is valued at $1,000 or more, a valid Virginia contractor's licence is required for the licence category in which the contractor is to work.^[5] Check the licence in DPOR's lookup before you agree to a price.

Permits are the building department's call. The Virginia building code's permit rule covers installations or alterations involving fuel supply systems, mechanical systems or electric wiring.^[2] Ask the business whether your repair needs one.

To see what a visit costs, read how much a pool heater repair visit costs in Virginia. If the heater is old, should I fix my pool heater or buy a new one helps you decide. You can also browse pool and spa equipment answers or find pool and spa businesses.

To get a technician to look at your heater, describe the pool heater problem and licensed local businesses reply.