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How to Troubleshoot an AquaStar Heater

The AquaStar heater is a tankless water heater manufactured by Bosch and designed for use in homes or small businesses. The tankless water heater has a full 12-year warranty if installed by a professional. Bosch provides a replacement part, free of charge, for any defective part during the warranty period. The cost of labor is the responsibility of the owner. Before requesting warranty service, troubleshoot the water heater.

No Pilot Spark

Step 1

Lift the flip-down cover on the front panel of the water heater and move the switch to the “On” position.

Step 2

Locate the fuse on the bottom corner of the electrical box. Remove and replace it if it is blown.

Step 3

Unscrew the water inlet hose on the water heater. Remove the inlet filter screen. Clean and replace it. Reinstall the water inlet hose.

Step 4

Turn off all faucets in the home. Remove the screw cap on the micro switch beneath the on/off switch. Turn the screw counterclockwise with a screwdriver until it sparks. Turn the screw clockwise 1 1/2 turns. Replace the screw cap.

Pilot Sparks but Does Not Ignite

Step 1

Turn a nearby hot-water faucet on and off to bleed air trapped in the gas line. Repeat until all air is removed.

Step 2

Pull off the temperature knob on the bottom of the heater and unscrew the knob collar to remove it. Grasp the main cover and lift it up and out. Blow through the gas orifice to remove dust and debris. Replace the main cover, knob collar and temperature knob.

Step 3

Remove the cap beneath the micro-switch assembly. Turn the adjustment screw counterclockwise slowly until the pilot ignites. Turn the screw clockwise 1 1/2 turns.

Water Too Hot or Too Cold

Step 1

Turn the temperature adjustment knob to the left to lower the water temperature, or to the right to raise it.

Step 2

Remove the water inlet hose on the water heater. Remove the inlet filter screen and clean it. Reinstall the water inlet hose.

Step 3

Open the main gas line fully to achieve sufficient gas supply and gas pressure.