Maintenance and service
5Maintenance and service
5.1Maintenance intervals
Warning: Failure to perform recommended maintenance may result in complete failure of the unit over time. The warranty does not cover failures due to improper or insufficient maintenance.
The GWH 425 PN requires periodic maintenance. The below time maintenance intervals should kept the unit operating for many years.
Every year
BInspect inlet water filter screen ( 5.2)
BInspect pilot assembly and flame ( 5.3)
BInspect burner assembly ( 5.4)
Every 2 years
BLubricate and clean water valve ( 5.2)
Every 3 to 5 years
BRebuild water valve ( 5.2)
BClean pilot assembly and clean or replace orifice ( 5.3)
5.2Water valve
The water valve is the main control that tells the heater to fire. If the periodic maintenance is neglected, more costly damage may occur over time.
Inspecting inlet water filter screen
Shut off the installer supplied cold water isolation valve to the heater. If one is not installed, install before proceeding. Open the nearest hot water tap to drain the plumbing lines. Position a bucket under the heater's water valve assembly to catch any water that may drain from the heater. Remove the filter retaining clip located at base of water valve (see Fig. 26). Remove the threaded bushing to access the cylindrical filter inside. Remove filter, clean with water and inspect for damage. If the filter is at all damaged, it should be replaced.
Lubricating the water valve
A more detailed instruction is available on our website at www.boschpro.com. Shut off the installer supplied cold water isolation valve to the heater. If one is not installed, install before proceeding. Open the nearest hot water tap to drain the plumbing lines. Position a bucket under the heater's water valve assembly to catch any water that may drain from the heater. Disconnect the inlet water pipe going to the back of the water valve. Disconnect the water pipe leading out of water valve to the heat exchanger. Do this by removing the retaining
clip on water valve assembly and pulling the pipe free from the water valve. Loosen the two set screws at the bottom of the water valve where it connects to the gas valve. If the set screws are seized, STOP and call Bosch tech support before proceeding. Forcing and snapping seized set screws may cause irrevocable damage to the water valve and gas valve assemblies. Remove the water valve by pulling it to the right. Separate the two halves of the water valve by removing the five screws on the left side of the water valve. Apply lithium or faucet & valve grease to the pushrod and o- ring. (See Fig. 29). Inspect the venturi and clean if necessary. (see Fig 29).
Rebuilding the water valve
Several parts within the water valve should be replaced every 3 to 5 years depending on water quality and usage. The parts list and instructions can be found on our website at www.boschpro.com. Failure to rebuild the water valve can result in decreased performance or damage to the heater.
5.3Pilot
Inspecting pilot
The pilot should burn with a clean sharp blue flame. The flame should fully engulf the tip of the thermocouple. If it does not, clean the pilot assembly per procedure below.
Cleaning pilot assembly
Shut off gas supply to the heater using installer supplied manual gas shutoff. Locate pilot gas tubing mounted in the center of the burner assembly. At the base of the pilot gas tubing there is a retaining clip. Release pilot gas tubing from this clip. Push upwards on other end of pilot gas tubing to release it from burner mount. Remove brass hex headed pilot orifice from gas valve (located near base of pilot gas tubing). Soak orifice and pilot gas tubing in carburetor cleaner for 30 minutes. Dry off and reinsert orifice in gas valve. If heater is an LP unit, replace orifice. Reinstall the pilot gas tubing following removal instructions in reverse. Open gas supply and return heater to service.
Caution: Do not ream or poke orifice as it will enlarge orifice opening.
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