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Bosch GWH-425-EF-N - User Manual

Bosch GWH-425-EF-N
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Water heaters for use with Natural and L.P.G.
GWH 425 EF
Flow Modulated with Electronic Ignition and Power Venting
Suitable for heating potable water only - Not approved for space heating purposes
(Intended for variable flow applications with steady cold water inlet temperatures)
GWH-425-EF-N
GWH-425-EF-L
6 720 607 017 US (03.10) JS
PRO TANKLESS
Warning: If the information in this manual is not
followed exactly. A fire or explosion may result
causing property damage, personal injury or death.
Do not store or use gasoline or other flammable
vapor and liquids in the vicinity of this or any other
appliance.
Improper installation, adjustment, alteration,
service or maintenance can cause injury or
property damage. Refer to this manual. For
assistance or additional information consult a
qualified installer, service agency or the gas
supplier.
In the Commonwealth of Massachusetts this
product must be installed by a licensed plumber or
gas fitter.
Upon completion of the installation, these
instructions should be handed to the user of the
appliance for future reference.
What to do if you smell gas
• Close gas valve. Open windows.
• Do not try to light any appliance
• Do not touch any electrical switch; do not use any
phone in your building
• If you cannot reach your gas supplier, call the fire
department.
• Immediately call your gas supplier from a neighbor’s
phone. Follow the gas supplier’s instructions.
• Installation and service must be performed by a
qualified installer, service agency or the gas supplier.

Table of Contents

Questions and Answers

  • J
    Jaime HolmesAug 14, 2025
    Why do the main burners go out during hot water use in my Bosch GWH-425-EF-N?
    • N
      Nicole CooperAug 14, 2025
      If the main burners on your Bosch Water Heater go out during hot water use, it could be due to several reasons. One potential cause is deficient exhaustion of flue gases. Another is a flow rate that has diminished below the activation rate; ensure that the water flow meets the required amount to activate the heater. Unbalanced pressure in waterlines, which can be resolved by ensuring faucet aerators or shower heads are free of minerals, can also cause this issue. The ECO (overheat sensor) might have tripped due to overheating, or the minimum inlet pressure on your well pressure tank might be inadequate, so check the inlet water pressure.
  • J
    Jeff RichardsAug 21, 2025
    Why is the water not hot enough in my Bosch GWH-425-EF-N Water Heater?
    • M
      Michael LangAug 21, 2025
      If your Bosch Water Heater's water is not hot enough, there are a few potential reasons. The temperature selection might be set too low, so try changing the setting. Insufficient gas pressure could also be the cause; it's crucial for tankless water heaters to have the correct gas line size to achieve proper gas pressure. Also, ensure your main gas line is fully opened in case of an insufficient gas supply. Cold water mixing with the hot water between the heater and the outlet could be another issue; compare the water temperature at the heater's outlet and at the tap. Finally, dirty or damaged parts in the water valve can prevent the gas valve from fully opening; inspect for damage or corrosion.
  • Z
    Zachary SmithAug 25, 2025
    Why does the hot water temperature fluctuate in my Bosch GWH-425-EF-N Water Heater?
    • R
      Ryan AndersonAug 25, 2025
      If you're experiencing hot water temperature fluctuations or unit deactivation with your Bosch Water Heater, several factors could be responsible. Unbalanced pressure in waterlines could be the problem, so make sure faucet aerators or shower heads are free of minerals. If the inlet water temperature to the water heater is very warm, temperature balance valves might be the issue. Cold water mixing with the hot water between the heater and the outlet could also be the cause. Erratic inlet water pressure due to inadequate supply water pressure or a saturated pressure tank on a well system might also be the reason, so check the inlet water pressure. Lastly, low gas pressure could be the culprit.
  • J
    John ElliottAug 27, 2025
    Why is the water too hot from my Bosch GWH-425-EF-N?
    • B
      Brenda BrockAug 27, 2025
      If your Bosch Water Heater is producing water that is too hot, it might be due to a few reasons. The temperature selection could be set too high. Additionally, the inlet water temperature might be very warm (60°-75°F). A clogged inlet filter screen restricting flow can also cause this issue; remove and clean the screen.
  • R
    raymond10Aug 31, 2025
    Why is the exhaust fan not operating on my Bosch Water Heater?
    • D
      Dustin RasmussenAug 31, 2025
      If the exhaust fan on your Bosch Water Heater isn't operating, start by checking the fuse and all electrical connections. Also, check the adjustment of the microswitch.
  • K
    Kevin MorseSep 3, 2025
    Why does the fan circulate when hot water is shut off in Bosch GWH-425-EF-N?
    • E
      Elizabeth PriceSep 3, 2025
      If the fan circulates even after the hot water is shut off in your Bosch Water Heater, check the adjustment of the microswitch.
  • M
    marshalllarrySep 6, 2025
    Why does the pilot spark continuously with no water running on my Bosch GWH-425-EF-N?
    • T
      timothyherreraSep 6, 2025
      If the pilot sparks continuously without any water running in your Bosch Water Heater, the microswitch may need adjustment.
  • L
    Lauren LittleSep 10, 2025
    Why does the fan operate without water flow in my Bosch Water Heater?
    • A
      Adrienne RiveraSep 10, 2025
      If the fan operates without water flow in your Bosch Water Heater, unplug the heater and first check that all electrical and electronic connections in the heater are clean and tight. Also, check the adjustment of the microswitch. The control box may need to be replaced.
  • S
    samuelkiddNov 17, 2025
    How to fix no spark at the pilot of Bosch GWH-425-EF-N Water Heater?
    • M
      Michael ThompsonNov 17, 2025
      If there's no spark at the pilot of your Bosch Water Heater, several issues could be the cause. Ensure the On/Off switch is in the 'On' position. Bad electrical connections could also be a factor. Insufficient water flow to activate the heater may be the cause; the water flow rate at the faucet must meet the minimum required. A bad fuse could also be the problem. If the water inlet filter is clogged, clean the water inlet filter screen. Check for cross-over in the water lines by shutting off the cold water supply and opening a hot water faucet. The microswitch may need adjustment or replacement. Ensure the cold incoming water connection is on the correct side of the heater. Check that the venturi is free of dirt particles, as water valve parts may be dirty or damaged. Poor circuit connecti...

Bosch GWH-425-EF-N Specifications

General IconGeneral
BrandBosch
ModelGWH-425-EF-N
CategoryWater Heater
LanguageEnglish

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