This system is unlikely to
require a By-pass unless all
radiators are thermostatically
controlled
Water Circulating Systems
The appliance is suitable for use with fully pumped
open vented systems (small bore and micro-bore),
gravity domestic hot water with pumped central heating
systems and sealed systems.
The following conditions should be observed on all
systems:
The static head must not exceed 30m (100ft) of
water.
The boiler must only be used with an indirect
cylinder.
Drain points should be fitted to the lowest points in
the system.
All electrical wiring, gas and water pipes must be
installed in a way which would not restrict the servicing
of the boiler.
Position isolating valves as close to circulating pump
as practicable.
For fuel economy and best boiler performance, the
system should be designed so that gravity circulation
does not take place in the heating system when the
pump is not running.
Treatment of Water Circulating Systems
For optimum performance after installation, this boiler and its
associated central heating system must be flushed in
accordance with the guidelines given in BS7593:1992
“Treatment of water in domestic hot water central heating
systems”.
This must involve the use of a proprietry cleanser, such as
BetzDearborn’s Sentinel X300 or X400, or Fernox’s Superfloc. Full
instructions are supplied with the products but for immediate
information please contact BetzDearborn on 0151 420 9563, or
Fernox on 01799 550811.
For long term protection against corrosion and scale, after flushing it
is recommended that an inhibitor such as BetzDearborn’s Sentinel
X100, or Fernox’s MB-1 or Copal is dosed in accordance with the
guidelines given in BS7593:1992.
Failure to flush and add inhibitor to the system may
invalidate the appliance warranty.
BYPASS REQUIREMENTS
The boiler is fitted with a pump overrun device which allows the
removal of residual heat from the boiler. NOTE: The pump overrun
will operate for approximately 3 minutes. The system design must
therefore always provide an open circuit for water to circulate
between the boiler flow and return.
If a system has an open circuit a bypass is not required.
A system using a 3 port diverter valve does not normally require a
bypass and therefore this system is recommended. The exception to
this is where all radiators in the system are fitted with thermostatic
valves, in which case a bypass would be required. However, if one
radiator in such a system was fitted with 2 lockshield valves a bypass
would not be required.
A system controlled by non-electrical valves e.g. mechanical
thermostatic control valves both on the radiators and the hot water
circuit and systems using twin zone valves (e.g. Honeywell 'S' Plan)
will require a bypass.
The bypass circuit can be:-
A) A minimum of 9 metres of 22mm pipe (measured between the
boiler flow and return connections). It should be fitted with a
lockshield valve opened at least 1 full turn to give a minimum flow rate
of 8 litres/min (1.8 gal/min).
B) A radiator fitted with lockshield valves. The radiator output should
be a minimum of 800 watts (2,700 Btu/h). Typically a convector type
radiator with an area of 3750 cm
2
(4ft
2
) is adequate.
C) By including an automatic bypass valve in the system (see
diagram).
D) Any circuit that provides the same operating conditions as option A
or option B.
Radiator Circuit
Examples of
Open Circuits
By-pass
Loops
SYSTEM DETAILS
(and By-pass Requirements)
Air Vent
Boiler
Pump
Radiator
Circuit
Fully Pumped System
Optional
Bypass
8
A By-pass is
required with
this system
Air
Vent
Radiator
Circuit
Twin Zone
Valve System
Air
Vent
Radiator
Circuit
3 Port Diverter
Valve System
Typical Systems Arrangement
B
F
R
B
C
C
A
A
Flow from boiler
Boiler
Pump
Valve
A = D. H. W. Zone valve
B = C. H. Zone valve
C = Automatic Bypass valve
Bypass length = A + B + C
Bypass Incorporating
Automatic Valve
Bypass Length
