Bosch 7 735 500 7848, Installation And Maintenance Instructions For Contractors

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Maintenance
W 120-5 O – 6 720 819 306 (2018/10)
29
9 Maintenance
▶ Allow the DHW cylinder to cool down sufficiently before performing
any maintenance.
▶ Carry out cleaning and maintenance procedures in the specified
intervals.
▶ Remedy all faults immediately.
▶ Only use original spare parts!
9.1 Maintenance intervals
Carry out the maintenance in accordance with flow rate, operating
temperature and water hardness (

Tab. 9, page 29).
The use of chlorinated potable water or a water softener unit reduces the
maintenance intervals.
You can check the water quality with your water supply utility.
Depending on the composition of the water, it can make sense to deviate
from the reference values listed.
9.2 Maintenance work
9.2.1 Testing the pressure relief valve
▶ Check the pressure relief valve annually.
9.2.2 Drain the DHW cylinder.
▶ Isolate the DHW cylinder on the domestic hot water side from the
piping. To do this, close the shut-off valves.
▶ Open a high-level tap to ventilate the system.
▶ Open the drain valve (

Fig. 3 [12], page 45).
▶ Close the drain valve again following maintenance.
▶ Test for tightness once it has been refilled (

Fig. 12, page 47).
9.2.3 Descaling/cleaning the DHW cylinder
▶ Drain the DHW cylinder.
▶ Check the interior of the DHW cylinder for contamination (limescale,
sediment).
▶ In the case of soft water:
Check the container regularly and clean to remove contamination.
-or-
▶ In the case of hard water or severe contamination:
Regularly descale the DHW cylinder in line with the actual amount of
limescale using chemical cleaning methods (e.g. with a suitable
descaling agent based on citric acid).
▶ Clean out the DHW cylinder interior with a water jet
(

Fig. 15, page 48).
▶ Use a wet & dry vacuum cleaner with plastic suction hose to remove
the residues.
▶ Seal the plug back into the inspection aperture
(

Fig. 16, page 48).
▶ Re-commission the DHW cylinder (

Chapter 6, page 28).
9.2.4 Checking the magnesium anode
The magnesium anode is a sacrificial anode, which is used up during
operation of the DHW cylinder.
▶ Shut off the cold water inlet.
▶ Depressurise the DHW cylinder.
▶ Remove and test the magnesium anode (

Fig. 17 to Fig. 20,
page 48).
▶ If the diameter is less than 15 mm, replace the magnesium anode.
Water hardness in °dH 3 – 8.4 8.5 – 14 > 14
Calcium carbonate
concentration in mol/ m³ 0.6 – 1.5 1.6 – 2.5 > 2.5
Temperatures Months
At a standard flow rate (< cylinder capacity/24 h)
< 60 °C 24 21 15
60 – 70 °C 21 18 12
> 70 °C 15 12 6
At a higher flow rate (>cylinder capacity/24 h)
< 60 °C 21 18 12
60 – 70 °C 18 15 9
> 70 °C 12 9 6
Table 9 Maintenance intervals in months
In order to improve the cleaning effect, heat up the heat
exchanger prior to cleaning it with a water jet. The
thermal shock effect separates deposits (e.g. limescale)
more readily.
If the magnesium anode is not properly serviced, this will
render the warranty on the DHW cylinder null and void.
Never bring the magnesium anode surface into contact
with oil or grease.
▶ Keep everything clean.