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Maintenance
4 Maintenance
The vent system must be inspected at regular 3-month
intervals. Points of inspection are as follows:
1. Screened opening of the vent hood should be free
from foreign material and cleaned as necessary.
2. Check all vent system connections for leakage
and reseal where needed with high temperature
silicone sealant. If any vent pipe component shows
signs of deterioration, replace immediately.
3. Inspect for proper closure of the back draft
flapper. If the flapper does not properly close,
there is a risk of freezing air coming across the
heat exchanger which may cause the pipes inside
to freeze and burst. This condition is not covered
by the water heater warranty. See Fig. 11A for a
properly closed back draft flapper.
4. Conduct safety interlock test and operation of
back draft flapper once a year (Chapter 3.1.3).
Fig. 11A Properly closed back draft flapper
Fig. 11B Improperly closed back draft flapper
10
5 Troubleshooting
5.1 Introduction
Many of the questions customers ask regarding
operation of this unit can be answered by following
the troubleshooting steps outlined below. Visit
our website at www.boschhotwater.com for more
detailed troubleshooting. For best results, perform
each step before proceeding to the next.
5.2 Power vent motor runs all the time or
intermittently without water flow
1. The power vent motor is flow switch activated.
If the internal paddle inside the flow switch is
jammed, it may constantly send a signal to turn on
the fan. Shut off water supply to heater and drain.
Remove flow switch from water heater piping by
removing clips on both ends. Flush water through
both ends of flow switch to free up internal paddle
and clear debris. After flushing, shake flow switch
up and down. The internal paddle should be heard
moving freely back and forth.
2. Large amounts of water demand can create
pressure drops throughout the plumbing. This
may allow for movement of the power vent flow
switch and activate the fan. Activated sprinkler
systems or flushed toilets are common causes for
this symptom. Consult a plumbing professional
to correct unintentional water flow through the
heater.
3. In buildings with excessively high water pressure,
a condition known as "water hammer" may exist.
This condition is caused by a combination of high
water pressure and the abrupt closing of a faucet
valve or internal washer/toilet valve. This instant
change in flow results in an instant change in the
internal pressures in the pipe, which then sends
a shock wave through the pipe. This physical
shock will shake, rattle or cause a loud bang in the
plumbing which is referred to as "water hammer."
Such a shock wave may cause movement of the
power vent flow switch which will activate the fan.
Consult a plumbing professional for the use of a
pressure reducing valve, expansion tank or water
hammer arrestor to combat this condition.
AQ4 Manual
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