Riello ALU PRO power Series Instructions For The Installer And The Technical Assistance Centre page 30

2. The heating systems
b
Topping up should not be dome using an automatic filling system, but rather done manually and should be recorded
in the service book.
b
If there are more than one boiler, they must all be put into service either at the same time or with a very short rotation
time so as to evenly distribute the limited quantity of initial lime-scale.
b
A flushing cycle must be programmed after the plant has been installed to flush out any installation debris.
b
Water used for filling or eventually topping up the system must always be filtered (synthetic or metal mesh filters
with filtering capacity of no less than 50 micron) to avoid deposits possibly triggering under-deposit corrosion.
b
The heating system must be flushed out and cleaned thoroughly before filling up the existing systems. The boiler
may not be filled until after the heating system has been flushed out.
2.1 New central heating systems
The system must be filled up slowly the first time; once it is filled and the air expelled it should never need to be topped
up again.
Systems should also be operated at maximum working temperature the first time they are started up, in order to facilitate
de-aeration. (Gas is not released from the water at low temperatures).
2.2 Reconditioning old central heating systems
If a boiler has to be replaced, do not refill the entire central heating circuit if the quality of water in it conforms to require-
ments. If the quality of water fails to conform to requirements, either recondition the old water or separate the water
circuits (water in the boiler circuit must conform to requirements).
3. Corrosion
3.1 Deposit corrosion
Under-deposit corrosion is an electrochemical process, due to the presence of sand, rust, etc., inside the mass of water.
These solid substances generally deposit on the bottom of the boiler (sludge), on tube and pipe heads or in the gaps
between pipes and tubes.
Micro-corrosion phenomena may be triggered off owing to the difference in electrochemical potential coming to be cre-
ated between the material in contact with the impurity and the surrounding one.
3.2 Stray current corrosion
Corrosion from stray currents can occur due to the differing electrical potentials between water in the boiler and the
metallic mass of the boiler or piping. This process leaves unmistakeable traces i.e. small regular conical holes.
b
All metallic parts should be grounded by an effective earth cable for this reason.
4. Eliminating air and gas from central heating systems.
If oxygen enters a circuit continuously or even intermittently (e.g. in under-floor heating systems whose pipes are not
protected by impermeable synthetic sheaths, in circuits with open expansion vessels, or in circuits that require frequent
top-ups) always separate the boiler's water circuit from the central heating circuit.
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INSTALLER