Bosch GWH 260 PN Service Bulletin Booklet page 6

OVERCOMING FLUCTUATING
TEMPERATURES
MODELS: 1000P, 1600P, 1600H
260PN, 425PN, 425HN
Introduction
Temperature fluctuations from hot to cold during use is typi-
cally caused by a back pr essure on the water flowing t hrough
the tankle ss water heater. This decreases the flow rate through
the tankless water heater belo w the required activation flow
rate and shuts the heater down. Follow these instructions step
by step to overcome this phenomenon.
Clean faucet aerators and shower heads
Check for restrictions in outlets, which would limit hot water
demand and may assist in de activation scenario. For sinks,
remove faucet aerator on end of sink. Flush and cle an screen
and reinstall. For showers, remove sho werhead and f lush. If
plugge d wit h mineral deposit s, cle an accor ding t o
manufacturer's suggestions or replace. (Note: if showerhead is
wand style/hand held, corrugated tube connecting to head may
be too restr ictive. Enlarging tube or using a normal showerhead
may be the solution.)
Clean Inlet filter screen
Inlet filter screen is located in bottom of the water valve near
the cold w ater connection side (right) at t he rear of the unit.
Please see bulletin CT-12 Cleaning inlet f ilter for more detailed
instr uctions.
Check for plumbing crossover
A plumbing crossover can be caused by a failed car tridge at a
single lever fauce t, incorrect plumbing or a faulty mixing valve
in the piping. The crossover will cr eate a back pressure on the
water heater and prevent an a dequate flow of w ater through it.
Close installer supplied cold water shut off valve to the heater
(if none installed, install bef ore proceeding). Open all ho t wa-
ter taps supplie d by the heater. Wait 5 minutes and check all
taps. Water running is a sign of a plumbing cross-over. Consult
a local plumber or service person for help in correcting a plumb-
ing crossover.
Confirm water pressure
Water pressure should stay above 30psi during operation. If on
a well system, we recommend a pressure setting of 40-60psi.
©BBT NORTH AMERICA CORPORATION
Bosch Group
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Lower temperature
The tem perature can be lowered by moving gas slide control to
the left. On models 1600H and 425HN, turn power adjustment
knob clockwise. See bulletin CT-07 Lowering temperatures for
alternative methods of lowering output temperature.
Confirm activation rate of the heater
1. Turn flow control knob on the front of heater fully clockwise.
2. Fully open one hot water tap.
3. Return to heater and shut cold water supply valve.
4. Slowly open cold water supply v alve until the burners ignite.
5. Return to hot water tap and measure f low rate by timing
how long takes to fill a quart container. A fill time of 30
seconds indicates a proper activation rate of 0.5 gallons per
minute (GPM)*. See Table 1 for other flow r ate conversions.
6. Repeat steps 4 and 5 a few times to check the accuracy of
test.
* A fill time less than 30 seconds indicates an activation rate
above the required 0.5GPM and a pos sible problem within
the heater's water valve. Periodic maintenance is required
on this water valve. Visit our w ebsite for par ts and ser vice
bulle tins for t his procedure.
GPM
.50
.75
1.00
1.25
1.50
1.75
2 .0 0
2 .5 0
3 .0 0
3 .5 0
4.00
TABLE 1
340 Mad River Park, Waitsfield, VT 05673
Y FL Y FL AMMABLE SO AMMABLE SO
Y FLAMMABLE SO Y FL AMMABLE SO AMMABLE SO
UTIONS WHEN UTIONS WHEN UTIONS WHEN
UTIONS WHEN
ORK T ORK T ORK TO THE HEA O THE HEA O THE HEA O THE HEATER TER TER TER
ORK T O THE HEA TER
Qu ar t Jar Gallo n Ju g
(in Secon ds) (in Seco nds)
30 1 20
20 80
15 60
12 4 8
10 4 0
8.5 34
7.5 30
6 24
5 20
4 .2 5 17
3.75 15
Bosch Water Heating
CT-06
page 1 of 1
rev 10/06