Gas powered (and electric heaters for that matter) heaters operate on a pressure switch and will not fire unless there is sufficient water flow. This it to prevent damage to the heater and surrounding plumbing, and to prevent fire. If your heater is not firing, consult the “Low Flow” tips section before considering any service. Gas heaters must be serviced by a licensed gas fitter. Beechmount Pools works with several gas fitters regularly and can recommend experienced pool heater service technicians.