Troubleshooting
6Troubleshooting
6.1Introduction
Many of the questions customers ask regarding operation of this unit can be answered by following the troubleshooting steps as outlined below. Visit our web site at www.boschpro.com for more detailed troubleshooting. For best results, perform each step before proceeding to the next. The suggested solutions may require that the cover be taken off. (See chapter 3.4).
6.2Pilot does not light
1.Verify gas supply is on at Natural Gas meter or Propane Tank. Make sure all manual gas shut off valves are in the open position. Have licensed gas technician confirm adequate gas pressure at the inlet tap (chapter 3.9). If gas is not present, verify manufacturer supplied Maxitrol regulator is in the upright position. The arrow on the back of the regulator should point in the same direction as gas flow.
2.If the unit was just installed or the gas lines have been worked on, there may be air in the gas line. Centered in the sparking position, hold down the gas control slide button while hitting the pilot igniter button every few seconds. It may take several minutes to bleed air out of the gas line.
3.Verify a spark is being thrown at pilot area while gas control slide button, centered in the single flame position, is being firmly depressed. Repeatedly push in pilot igniter button to light the pilot. If no spark is present, verify proper wire connection to the electrode.
4.Pilot assembly may be blocked. Clean or replace the pilot orifice (chapter 5.3).
6.3Pilot lights, but goes out when button is released
1.When lighting pilot ensure the gas control slide button is fully depressed and held down for at least 20 seconds after pilot is lit.
2.Verify gas type indicated in rating sticker located on right hand side of cover, coincides with the gas type you are using. NG is a natural gas unit and LP is for liquid propane.
3.If using a power vent, check the safety spillage switch reset button (the safety spillage switch is wired through the water heater's thermocouple circuit). The spill switch should be located at top of water heater close to draft diverter (Consult manual that came with powervent).
4.Check all connections of the pilot safety circuit. The pilot safety circuit consists of a thermocouple, overheat sensor (ECO), flue gas sensor, safety spillage switch(models with Powervents only) and the
electromagnet (See parts diagram for locations). Clean sensor connections with light sandpaper if corrosion is evident. The electromagnet connection is 5mm nut from the thermocouple which screws into a larger 17mm nut. Tighten both nuts snugly but do not over tighten.
5.Pilot flame should be blue in color and completely engulfing the tip of the thermocouple. If not, have a licensed gas technician verify gas pressure is in accordance with manufacturer's specifications (chapter 3.9) and clean or replace the pilot orifice
(chapter 5.3).
6.Have a licensed gas technician verify the proper operation of the thermocouple by measuring the millivoltage from the thermocouple lead to ground. The proper reading should be 24mVDC or greater. If the reading is lower, the thermocouple may be defective. Call Bosch Water Heating for further instructions.
6.4Pilot goes out during or after hot water use
1.Pilot outage during use typically results from the unit's safety overheat/high limit sensors interrupting the pilot circuit. The GWH 425 PN does not have a thermostat. If inlet water is preheated, the unit will overheat, stopping the flow of gas. Plumb inlet with a cold water line only.
2.Failure to vent properly by reducing pipe diameter, improper use of elbows or not meeting required vent length are common causes that deactivate the pilot safety circuit. Confirm venting is in accordance with manufacturer's specifications (see chapter 3.7).
3.Confirm the combustion air requirements are being met in accordance with manufacturer's specifications (see chapter 3.6). Proper venting and combustion air will ensure a proper draft.
4.Confirm that the burners in the water heater go off immediately when the hot water is turned off. If they remain on or shut down slowly, then the overheat sensor (ECO) will interrupt the pilot circuit and shut off all gas to the heater. The water valve assembly, which actuates the burners, may be dirty and require periodic maintenance (every 2 - 5 years depending on water quality and use) (see chapter 5.2).
5.Check all connections of the pilot safety circuit. The pilot safety circuit consists of a thermocouple, overheat sensor (ECO), flue gas sensor, safety spillage switch(models with Powervents only) and the electromagnet (See parts diagram for locations). Clean sensor connections with light sandpaper if corrosion is evident. The electromagnet connection is 5mm nut from the thermocouple which screws into a larger 17mm nut. Tighten both nuts snugly but do not over tighten.
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