SECTION 3
POTTERTON COMMERCIAL PRODUCTS DIVISION
INSTALLATION, OPERATION & MAINTENANCE MANUAL
PAGE 8
NXR3
Boilers operating under constant flow conditions can
be more accurately controlled and are not subject to
excessive temperature stresses.
The boilers
MUST NOT
be fired under any
circumstances with less than the minimum water flow.
On systems with variable flow rates due to flow
reducing devices, ie. TRVs, zone valves, etc, or where
the minimum heat demand, ie. summer domestic hot
water load, does not achieve the minimum boiler flow
rate then consideration shall be given to incorporating
a primary loop system.
It is recommended that the system is designed to give
a constant boiler flow rate.
BOILER PROTECTION
The provision of pump overrun by a time delay relay
or a thermostat situated in the flow pipe close to the
boiler is essential to remove residual heat from the
boiler, see Fig. 21, section 6.
Unions and isolating valves should be fitted to the flow
and return manifolds so that the boiler can be isolated
from the system if the need arises. Your legal
obligations must be adhered to. (i.e. appropriate
safety valves must be fitted).
SYSTEM WATER QUALITY
High efficiency boiler systems require the water
quality of the system water to be controlled by the use
of inhibitors to maintain a neutral Ph and inhibit
corrosion. Additionally the water system should be
free of leaks to prevent raw water make up which will
dilute any inhibitors, promote corrosion and form lime
scale.
Existing Systems
On existing systems where boilers are being replaced
due to failure then the cause should be investigated
before installing new boilers. This can normally be
achieved by cutting open a failed boiler section and
examination for system debris or contamination.
Lime scale is a positive indicator of continuous system
water make up due to water loss. Evidence of
magnetite (black sludge) in the system and the
formation of gas in radiators causing air locking is a
positive indicator of corrosion.
Where an old system shows evidence of
contamination then system cleaning should be carried
out before installation of new boilers. The heating
system should be chemically flushed to remove any
lime scale or corrosion and a corrosion and lime scale
inhibitor added. Lime scale descalers if incorrectly
used could cause any remaining system debris to
continue to breakdown and contaminate the new
boiler causing boiler failure.
Advice on system cleaning and suitable products
should be sought from specialist suppliers of system
cleaners such as Fernox or Sentinel.
It is important to note that corrosion inhibitor can only
be used in an attempt to prevent corrosion from
occurring, where a system has an existing corrosion
problem, inhibitors will be ineffective and the system
requires cleaning.
On existing systems where comprehensive descaling
and desludging cannot be carried out then
consideration should be given to separating the new
boiler system from the existing system pipe work by
the use of plate heat exchangers.
New Systems
New pipe work systems should be thoroughly flushed
with a suitable cleaning agent to remove debris and
flux residues before filling. The system water should
be dosed with a suitable corrosion and lime scale
inhibitor.
System Water Monitoring
The system water should be monitored as part of a
maintenance programme to ensure the following:-
Raw water make up is not occurring.
Corrosion and lime scale Inhibitors are still active
Water Ph is below Ph 8.5 other wise on systems with
aluminium content, component failures may occur.
SEALED SYSTEMS
General
Potterton Commercial boilers are suitable for use on
sealed systems designed in accordance with BS
6644: 2005 and BS 6880 Part 2. In addition,
reference should be made to the Health & Safety
Executive guidance note PM5 "Automatically
Controlled Steam & Hot Water Boilers".