12
Filling the system
Recommendation
It is recommended that each system
should be filled or refilled with treated
water and specialist firms will be able to
advise in this respect
Water treatment
There is basic need to treat water contained
in all heating and indirect hot water systems,
particularly open vented systems.
One millimetre of lime reduces the heat conversion
from flame via metal to water by 10%.
In practice the deposition of these salts is liable
to cause noises from the boiler body or even
premature boiler failure. Corrosion and the
formation of black iron oxide sludge will ultimately
result in premature radiator failure.
Open vented systems are not completely sealed
off from the atmosphere as it is essential to
provide a tank open to atmosphere if proper
venting and expansion of system water is to be
achieved. The same tank is used to fill the water
and it is through the cold feed pipe that system
water expands into the tank when the boiler
passes heat into the system.
Conversely when the system cools, water
previously expanded is drawn back from the
tank into the system together with a quantity of
dissolved oxygen.
Even if leakage from the heating and hot water
systems is eliminated there will be evaporation
losses from the surface of the tank which,
depending on ambient temperature, may be high
enough to evaporate a large portion of the system
water capacity over a full heating session.
There will always be corrosion within a heating
hot water system to a greater or lesser degree
irrespective of water characteristics unless the
initial fill water from the mains is treated. Even
the water in closed systems will promote corrosion
unless treated.
For these reasons Hoval strongly recommend
that when necessary the system be thoroughly
cleaned, prior to the use of a stable inhibitor, which
does not require continual topping up to combat
the effects of hardness salts and corrosion.
Hoval advise contact directly with major specialists
on water treatment such as Grace & Dearborn or
Houseman..
Check the following:
• all connections are made and tightened
• instrument pockets are fitted and water tight
• spare sockets are fitted with plugs and are
water tight
• all valves in the heating circuit are open
• mixing or diverting valves are opened half
way,
then gradually fill with water until the altitude
gauge (if fitted) indicates the correct head
and
the header tank is filled to appropriate level
• the installation is completely vented
• if a pressurisation unit is installed reference
should be made to the makers filling
instructions and applied
• installation debris and any deposits from the
system are not allowed into the boiler
• the boiler is flushed out through the drain
connection to ensure that the boiler is clean
inside
• a large strainer is fitted to older systems to
remove deposits before the return enters the
boiler.
Important
The whole system must be thoroughly
flushed with water to wash out foreign
matter and impurities in accordance
with CIBSE/BSRIA guidelines.
Filling the System
August 2014
