MEGAFLO 2sf User manual

Megaflo Compact SystemReady
Hot Water Cylinders
Unvented Indirect
Important
Please read & understand all these instructions before commencing installation.
Please leave this manual with the customer for future reference
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2
Contents
1. Introduction................................................................................................. 3
1.1 General......................................................................................................3
1.2 Symbols used............................................................................................ 3
1.3 Abbreviations ........................................................................................... 3
1.4 Liabilities................................................................................................... 3
2. Safety........................................................................................................... 4
2.1 General safety warnings ........................................................................... 4
3. Technical specifications .............................................................................. 5
3.1 Technical data........................................................................................... 5
3.2 Dimensions............................................................................................... 6
3.3 Electrical diagram(s) .................................................................................. 7
4. Description of the product......................................................................... 8
4.1 General description................................................................................... 8
4.2 Operation principle ................................................................................... 8
4.3 Main components..................................................................................... 8
4.4 Standard delivery ...................................................................................... 8
5. Before installation ...................................................................................... 8
5.1 Installation regulations.............................................................................. 8
5.2 Installation requirements........................................................................... 8
5.3 Choice of location .................................................................................... 9
5.4 Transport .................................................................................................. 9
6. Installation ................................................................................................ 10
6.1 General .................................................................................................. 10
6.2 Water connections.................................................................................. 11
6.3 Electrical connections.............................................................................. 18
6.4 Filling the installation .............................................................................. 19
7. Commissioning.......................................................................................... 20
7.1 General .................................................................................................. 20
7.2 Checklist before commissioning.............................................................. 20
7.3 Commissioning procedure ...................................................................... 20
8. Operation .................................................................................................. 21
8.1 General .................................................................................................. 21
9. Maintenance ............................................................................................. 22
9.1 General .................................................................................................. 22
9.2 Standard inspection & maintenance operations....................................... 22
10. Troubleshooting...................................................................................... 23
10.1 Fault finding ......................................................................................... 23
11. Decommissioning.................................................................................... 24
11.1 Decommissioning procedure................................................................. 24
12.1 Spare parts list ...................................................................................... 25
Benchmark checklist ..................................................................................... 30
Commissioning & service records.................................................................31
Warranty........................................................................................................ 32
THE BENCHMARK SCHEME
Benchmark places responsibilities on both manufacturers and installers. The purpose is to ensure that customers are provided
with the correct equipment for their needs, that it is installed, commissioned and serviced in accordance with the manufacturer’s
instructions by competent persons and that it meets the requirements of the appropriate Building Regulations and relevant
electrical qualifications. The Benchmark Checklist can be used to demonstrate compliance with Building Regulations and
should be provided to the customer for future reference. Installers are required to carry out installation, commissioning and
servicing work in accordance with the Benchmark Code of Practice which is available from the Heating and Hotwater Industry
Council who manage and promote the Scheme. Visit www.centralheating.co.uk for more information.

3
1. Introduction
1.1 General
The following instructions are offered as a guide to the
user and installer.
The installation must be carried out by a competent
plumbing and electrical installer in accordance with
Building Regulation G3 (England and Wales), Technical
Standard P3 (Scotland) or Building Regulation P5
(Northern Ireland) and the Water Fitting Regulations
(England and Wales) or Water Byelaws (Scotland).
1.2 Symbols used
In these instructions, various risk levels are employed to
draw the user’s attention to particular information. In
doing so we wish to safeguard the user, avoid hazards
and guarantee the correct operation of the appliance.
DANGER
Risk of a dangerous situation causing serious
physical injury.
WARNING
Risk of dangerous situation causing slight
physical injury.
CAUTION
Risk of material damage.
 Signals important information.
1.3 Abbreviations
`T&P - Temperature & Pressure Relief Valve
`PRV - Pressure Reducing Valve
`ERV - Expansion Relief Valve
1.4 Liabilities
Manufacturers liability
Our products are manufactured in compliance with
the requirements of the various applicable European
Directives.
This appliance complies with the requirements of the CE
marking directive.
In the interest of UK customers, we are continuously
endeavouring to make improvements in product quality.
All the specifications stated in this document are therefore
subject to change without notice.
Our liability as the manufacturer may not be invoked in
the following cases:
`Failure to abide by the instructions on using the
appliance.
`Faulty or insufficient maintenance of the appliance.
`Failure to abide by the instructions on installing the
product.
Installer's liability
The installer is responsible for the installation and the
commissioning of the appliance. The installer must
respect the following instructions:
`Read and follow the instructions given in the manuals
provided with the appliance.
`Carry out installation in compliance with the
prevailing legislation and standards.
`Perform the initial start up and carry out any checks
necessary.
`Complete the commissioning checklist.
`Explain the installation to the user.
`If maintenance is necessary, warn the user of the
obligation to check the appliance and maintain it in
good working order.
`Give all the instruction manuals to the user.
Users liability
To guarantee optimum operation of the appliance, the
user must respect the following instructions:
`Read and follow the instructions given in the manuals
provided with the appliance.
`Call on qualified professionals to carry out installation
and initial start up.
`Get your installer to explain your installation to you.
`Have your required checks and services done.
`Keep the instruction manuals in good condition and
close to the appliance.
This appliance can be used by children aged from 8 years and above and persons with
reduced physical sensory or mental capabilities
or lack of experience and knowledge if they
have been given supervision or instruction
concerning use of the appliance in a safe way
and understand the hazards involved. Children
shall not play with the appliance. Cleaning and
user maintenance shall not be made by children
without supervision.
Children must be supervised to ensure they do
not play with the appliance.

4
2. Safety
2.1 General safety warnings
WARNING TO USER
`If water discharges from the
Temperature/Pressure Relief /Expansion
Relief Valve on the cylinder shut down
the boiler/immersion heaters. Do not
turn off any water supply. Contact a
competent installer for unvented water
heaters to check the system.
`Do not tamper with any of the safety
valves fitted to the system. If a fault is
suspected contact a competent installer.
`DO NOT bypass the thermal cut-out(s) in
any circumstances.
WARNING
`Only competent persons having received
adequate training are permitted to work
on the appliance and the installation.
`Do not tamper with any of the safety
valves or controls supplied with the
cylinder.
`Before any work, switch off the mains
supply to the appliance and the water
mains.
`Do not switch on if there is a possibility
that the water in the cylinder is frozen.
DANGER
This cylinder is unvented and as such becomes
pressurised when in operation. The combination
of pressurisation and hot water could lead to
serious physical injury if the safety instructions in
this manual are not adhered to.
CAUTION
Do not operate immersion heaters until the
appliance has been filled with water.
WARNING
When handling the appliance, take appropriate
precautions for the weight of the unit. Weights
can be found in section 3, table 1, page 5.
CAUTION
Annual maintenance is recommended by a
competent person.

- Water may drip from the discharge pipe of
the pressure-relief device and this pipe must
be left open to the atmosphere; (see page 17
for more details)
-The pressure-relief device is to be operated
regularly to remove lime deposits and to verify
that it is not blocked; (see page 22 for more
details)
- How hot water can be drained. (see page 22
for more details)
- The type or characteristics of the pressure-
relief device and how to connect it; (see Figure
9, page 13 and Figure 10, page 14 for details)
- A discharge pipe connected to the pressure-
relief device is to be installed in a continuously
downward direction and in frost free
environment; (see page 17 for details)
Details on how to set the temperature
controls for both immersion heaters and boiler
controls can be found in section Installation
Instructions, and Figure 16, page 19.

5
3. Technical specifications
3.1 Technical data:
Notes:
1. Indirect cylinders tested in accordance with BS EN 12897:2006.
2. Heat up time from cold through 45°C, based on a flow temperature of 80°C +/- 2°C & normal volume.
Table 1: Technical data - Indirect
Model(s) 2sr 4sr 6sr 8sr
Energy efficiency class C C C C
Storage volumes V in Litres 137 155 178 195
Standing loss in W 65.8 66.3 75.8 82.1
Table 2: Technical parameters in accordance with European Commission regulations 814/2013 and 812/2013
2sf 4sf 6sf 8sf
Max direct kW rating 3 3 3 3
Immersion heat up times
(Btm immersion, 3kW)
139 167 179 208
Coil surface area (m²) 0.51
Coil heat up times
15l/min 33.1 40.1 43.0 45.1
30l/min 26.9 30.2 34.8 37.7
45/min 25.0 28.8 32.3 34.2
Coil rating (kW) ²
15l/min 13.1 12.7 13.7 14.3
30l/min 16.3 16.3 17.1 17.3
45l/min 17.6 17.7 18.8 19.1
Pressure drop through
coil
15l/min 0.004 MPa (0.04 Bar)
30l/min 0.013 MPa (0.13 Bar)
45l/min 0.031 MPa (0.31 Bar)
Heat loss (kW/24hrs) 1.58 1.59 1.82 1.97
Weight empty (kg) 41 46 50 53
Weight full (kg) ¹ 178 201 228 248
Volume (Litres) ¹ 137 155 178 195
Mixed water delivery to 40°C1168 188 218 238
Max mains pressure 1.6 MPa (16 Bar)
Max design pressure 0.8 MPa (8 Bar)
Operating pressure/PRV set pressure 0.3 MPa (3 Bar)
Max primary pressure ³ 1.0 MPa (10 Bar)
Expansion relief valve setting 0.8 MPa (8 Bar)
T&P valve setting 90°C +/- 5°C/1.0 MPa (10
Bar)
T&P Part number 7034796
Immersion heater electrical rating 3.0 kW@240V/2.8kW@230V
~

6
3.2 Dimensions and connections
Figure 1: General dimensions - SystemReady
Table 3: General dimensions table - SystemReady
Size DIMENSIONS (mm)
ABC
2sr N/A 728 1130
4sr N/A 883 1256
6sr N/A 1008 1413
8sr 900 1084 1515
355
A
B
C
316
423
619
689
759
350 285
285415

7
Figure 2: Schematic wiring diagram - basic 2 x 2 port valve system
3.3 Electrical diagram
KEY
Br BROWN
Bl BLUE
G GREY
O ORANGE
W WHITE
GY GREEN/YELLOW
DHW DOMESTIC HOT WATER
HTG HEATING
L LIVE
N NEUTRAL
EARTH
BOILER
(DHW)
ZONE VALVE
WIRING CENTRE
1239 10
L N
G
Br Bl O
GY
2
13
L N
L
N
PUMP
INDIRECT
THERMAL CONTROLS
(SUPPLIEDFITTED)
FUSED (3AMP)
MAINS SUPPLY
N.B. A DOUBLE POLE ISOLATING
SWITCH MUST BE INSTALLED IN
THE MAINS SUPPLY
NOTES
1. ALL EARTH CONNECTIONS MUST BE LINKED BACK TO THE EARTH TERMINALS IN THE WIRING CENTRE
2. ALL NEUTRAL CONNECTIONS MUST BE LINKED BACK TO THE NEUTRAL TERMINALS IN THE WIRING CENTRE
3. ASSUMES BASICBOILER
4. THE 22MM MOTORISED VALVES DO NOT HAVE A WHITEWIRE
5. THE ABOVE DIAGRAM IS FOR GUIDANCE ONLY, THE MANUFACTURER ACCEPTS NO LIABILITY FORANY LOSS OR DAMAGE ARISING FROM
ANY ERRORS OR OMISSIONS THAT MAY BE INADVERTENTLYCONTAINED WITHIN THIS DIAGRAM. THE VARIOUS EQUIPMENT
MANUFACTURERS SHOULD BE CONSULTED TO CONFIRM THE CORRECT OPERATION OF THEIR PRODUCTS WITHIN THE SYSTEM
11 13
12 14 15 16
N
N
N
N
(SUPPLIED FITTED)
(SUPPLIED FITTED)
PROGRAMMER - HEATING ZONE
1
& DOMESTIC HOT WATER
(SUPPLIED)
L N
HTG DHW
ON ON
4 3 5 6
ROOM SENSOR
(SUPPLIED)
N
HEATING ZONE 1VALVE
G
Br Bl O
GY
N
(SUPPLIED FITTED)
W
HEATING ZONE 2 VALVE
G
Br Bl O
GY
N
W
PROGRAMMABLE
ROOM THERMOSTAT
FOR ZONE 2
12
45 678

8
5.1 Installation regulations
5.2 Installation requirements
Water supply
In an unvented system the pressure and flowrate is directly
related to the incoming water supply. For this reason it
is recommended that the maximum water demand is
assessed and the water supply checked to ensure this
demand can be satisfactorily met.
`We suggest the minimum supply requirements
should be 0.15MPa (1.5 bar) pressure and 20 litres
per minute flow rate. However, at these values outlet
flow rates may be poor if several outlets are used
simultaneously.
`A 22mm cold water supply is recommended,
however, if a smaller supply exists, which provides
sufficient flow, this may be used (although more
flow noise may be experienced).
`The higher the available pressure and flow rate the
better the system performance.
`See table 1 on page 5 for appliance operating
pressures. This is controlled by the Pressure Reducing
Valve.
`The water supply must be of wholesome water
quality (Fluid Category 1 as defined by the Water
Supply Regulations 1999).
Outlet/terminal fittings (taps, etc.)
`The appliance can be used with most types of
terminal fittings.
`Outlets situated higher than the appliance will give
outlet pressures lower than that at the heater, a
10m height difference will result in a 1 bar pressure
reduction at the outlet.
`All fittings, pipe work and connections must have a
rated pressure of at least 8 bar at 80°C.
4. Description of the product
4.1 General description
This appliance is a purpose designed unvented water
heater. The unit has a stainless steel inner vessel, which
ensures an excellent standard of corrosion resistance. The
outer casing is a combination of resilient thermoplastic
mouldings and pre-coated steel. All products are
insulated with CFC free polyurethane foam to give good
heat loss protection.
The appliance is supplied complete with all the necessary
safety and control devices needed to allow connection to
the cold water mains. All these components are preset
and should not be tampered with.
4.2 Operation principle
The unvented cylinder is used to heat and store hot water
for use in domestic applications.
The water can be heated indirectly through a coil in the
unit using an indirect heat source, or directly via back up
immersion heater.
4.3 Main connections
See Figure 4: Main connections on page 10
4.4 Standard delivery
The delivery includes:
`Cylinder
`Factory fitted
`Immersion heater(s) and thermal controls
`Combination Temperature and Pressure Relief
Valve (set at 90ºC / 1 Mpa (10bar)) with Expansion
Relief valve (set at 0.8Mpa (8Bar))
`Indirect thermostat and thermal cut-out
`Tundish
`Drain valve
`Wiring centre
`2 x 2 Port motorised valve
`Lock shield flow balancing valve
`Filling Loop
`Automatic air vent
`3 bar Pressure Reducing Valve (incorporating strainer)
`Isolating valve
`Mixing valve
`Mixing valve connection pipe
`Literature pack
`Instructions (inc benchmark commissioning
checklist & service record)
`Warranty card
Check all components are supplied in the pack and advise
your supplier if any are missing
5. Before installation
WARNING
Installation of the appliance must be carried
out by a qualified engineer in accordance
with prevailing and national regulations as
listed below.
`Building Regulations G3
`The Building Standards (Scotland)
`The Building Regulations (Northern
Ireland)
`I.E.E Electrical Regs
`UK Water Regulations

9
Limitations
The appliance should not be used in association with
any of the following:
`Solid fuel boilers or any other boiler in which the
energy input is not under effective thermostatic
control, unless additional and appropriate safety
measures are installed.
`Ascending spray type bidets or any other class 1 back
syphonage risk requiring that a type A air gap be
employed.
`Steam heating plants unless additional and
appropriate safety devices are installed.
`Situations where maintenance is likely to be neglected
or safety devices tampered with.
`Water supplies that have either inadequate pressure
or where the supply may be intermittent.
`Situations where it is not possible to safely pipe away
any discharge from the safety valves.
`In areas where the water consistently contains a high
proportion of solids, e.g. suspended matter that
could block the strainer, unless adequate filtration
can be ensured.
`In areas where the water supply contains chloride
levels that exceed 250mg/l.
`Gravity circulation primaries.
5.3 Choice of location
The cylinder must be vertically floor mounted. Although
location is not critical, the following points should be
considered:
`The appliance should be sited to ensure minimum
dead leg distances, particularly to the point of most
frequent use.
`Avoid siting where extreme cold temperatures will
be experienced. All exposed pipe work should be
insulated.
`The discharge pipe work from the safety valves must
have minimum fall of 1:200 from the appliance and
terminate in a safe and visible position as per G3
regulations.
`Access to associated controls and immersion heaters
must be available for the servicing and maintenance
of the system. Where these controls are installed
against a wall a minimum distance of 250mm must
be left.
`Ensure that the floor area for the appliance is level
and capable of permanently supporting the weight
when full of water (see table 1, page 5 for weights).
`The tundish should be installed away from electrical
components.
5.4 Transport
If the unit is to be stored before installation it must be
placed upright on a secure, level surface and be in a dry,
frost free environment. The support surface must be
capable of supporting the packaged weight of the unit,
the packaged weights are displayed on the carton label.
Please take care when handling a packaged appliance.
The appliance is heavy and must only be moved manually
using safe working practices. The package weights of
each unit are displayed on the carton label.
Take note of the unit weights when deciding on a safe
lifting method. DO NOT use the factory fitted T&P/
Expansion Relief Valve to lift or manoeuvre the unit.
WALL
Min 250mm Min 250mm
Figure 3: Siting the appliance

10
6. Installation
6.1 General
After reading the previous sections in this booklet and
choosing a suitable location for the appliance please
install, paying attention to the following water, electrical
and commissioning sections.
Boiler selection
`Ideally the boiler should be a system type boiler
incorporating the primary circulating pump, primary
expansion vessel and Pressure Relief device, a non
system boiler can be used however suitable controls
must be incorporated into the primary circuit
according to manufaturers instructions.
Figure 4: Typical installation schematic (not to scale)
`The boiler should have a control thermostat and non
self-resetting thermal cut-out and be compatible
with unvented storage water heaters.
`Should be a sealed system - maximum primary
pressure 3 bar.
`The primary flow from the boiler must be pumped.
Gravity circulation will not work due to the
special design of the primary heat exchanger. It is
recommended that the automatic air vent supplied is
incorporated in the primary return pipework close to
the unvented system.
`The boiler cannot be vented through the cylinder.
TO HOT OUTLET
DISCHARGE PIPE
DRAIN COCK
T&P and EXPANSION RELIEF VALVE
BALANCED COLD WATER
CONNECTION (IF REQUIRED)
MIXING VALVE
PRIMARY
FLOW
PRIMARY
RETURN
3 BAR PRESSURE REDUCING
VALVE WITH STOP COCK
TUNDISH
ELEMENT CONTROLS
HOUSING
MAINS WATER
SUPPLY

11
6.2 Water connections
WARNING
`Under no circumstances should the
factory fitted Temperature/Pressure/
Expansion Relief Valve be removed other
than by a competent person. To do so
will invalidate any warranty or claim.
`The cold water controls MUST be
fitted on the mains water supply to the
appliance.
`No control or safety valves should be
tampered with or used for any other
purpose.
`The discharge pipe should not be blocked
or used for any other purpose.
`The tundish should not be located
adjacent to any electrical components.
Refer to the installation schematic (fig 11, page 14) for
details on the pipe work layout. Specific details for the
discharge pipe work layout are also provided in figure 12
on page 17, see also Figure 6 page 12 for Primary circuit
schematic
`The connection points to the heating system are
in 22mm O/D copper pipe for 2sr, 4sr, 6sr, and 8sr
units.
`All pipe fittings are made via 22mm compression
fittings directly to the unit (nuts and olives supplied).
`Solder fittings can be used, but extreme care must be
taken to ensure the external finish of the appliance
casing is not damaged by heat.
`Push fit type fittings can be used for connection to
the copper pipes.
`The cold water inlet control kit supplied with the
appliance incorporates a full flow isolating valve
which will enable the appliance to be isolated from
the mains supply for maintenance or servicing.
`It is recommended that the outlet point of the drain
pipework be at least 1 metre below the level of
the base of the appliance (this can be achieved by
attaching a hose to the drain tap outlet spigot).
Mixing valve
`The mixing valve should be installed at the hot
outlet point of the appliance using the copper tube
supplied.(see figure 5) The mixing valve will reduce
the hot water outlet temperature to approx 55°C,
further temperature control will be required for outlets
such as showers and baths
`The mixing valve can be installed in any orientation
providing the pipe from the tank outlet to the H port
of the valve is no more than 500mm long and has no
other connections attached
`Where the application dictates water to be delivered
at 60°C, a mixing valve pre-set at 60°C is available
as an accessory (see page 25) note the overall mixed
water volume would decrease
Cold water control pack
CAUTION
`Flush supply pipe work before
connection to remove all flux and debris
prior to fitting the inlet controls. Failure
to do this may result in irreparable
damage to the controls and will
invalidate any warranty.
`The cold water control pack can be connected
anywhere on the cold water cylinder supply.
`The Control pack incorporates the Pressure Reducing
Valve and Isolation valve
`The pressure setting is set to 0.3Mpa/3.0 bar. It is not
adjustable.
`The valve can be fitted in any orientation to suit
the installation as long as the valve is installed with
the direction of flow arrows pointing in the correct
direction.
`The Expansion Relief has been incorporated into the
T&P Valve for ease of installation
`No other valves should be placed between the cold
pressure reducing valve and the appliance.
`Where discharge pipework is difficult to attain, the
local building control officer from the local council
should be sought for advice as this falls under G3
guidelines and is not down to the manufacturer for
unvented systems
Primary circuit control
`Primary circulation to the cylinder heat exchanger
must be pumped; gravity circulation WILL NOT
WORK.
`It is recommended that the automatic air vent
supplied is incorporated in the primary return pipe
work close to the unit.
`Boiler flow temperature should be set to 80° (peak
temperature to primary heat exchanger 88°C).
`See Fig 6 page 12 for example installation schematic,
consult boiler manufatuers installation manual for
further guidance. Other primary system valves may
be required
Hot water from
cylinder
Cold water from
Mains
Mixed water
Mixer Valve
Copper tube
H
M
C
Figure 5: Mixing valve layout

12
Secondary circulation
If secondary circulation is required it is recommended
that it be connected to the appliance as shown (see fig
7).
`The secondary return pipe should be in 15mm pipe
and incorporate a check valve to prevent backflow.
`A suitable WRAS approved circulation pump will be
required.
`On large systems, due to the increase in system
water content, it may be necessary to fit an
additional expansion vessel to the secondary circuit.
This should be done if the capacity of the secondary
circuit exceeds 10 litres.
Pipe capacity (copper):
15mm O.D. = 0.13 l/m (10 litres = 77m)
22mm O.D. = 0.38 l/m (10 litres = 26m)
28mm O.D. = 0.55 l/m (10 litres = 18m)
Note: Plastic pipe capacities may be reduced due to
thicker wall sections.
Cold Water
Inlet
To Hot
Outlets
Check Valve
Swept Tee
Secondary
Return
Secondary
Circulation Pump
Figure 7: Secondary circulation schematic
M
M
1
2
3
4
5
6
7
8
9
1 System boiler complete
2 SystemReady Unit
3 Filling loop assembly
4 Lockshield balancing valve
5 DHW Motorised valve
6 Drain off cock
7 CH motorised valve
8 Tapping for Zone 2 CH motorised valve
9 CH circuit
Figure 6: Primary circuit schematic

13
Figure 8: 3 bar Pressure Reducing Valve
Mains in
22mm compression connections
Outlet to Megao
Take note of ow
direction
Pressure reducing valve
cartridge (3 bar)
Figure 7: Secondary circulation schematic
Combination T&P/ERV
T&P = Temperature and Pressure
ERV = Expansion Relief Valve
Mains water
supply
90° Tundish
T&P
actuation knob
ERV
actuation knob
D2 Pipe
Figure 9: Isolation and 3 bar pressure reducing valve
Figure 10: Combination T&P/Expansion Relief Valve
Isolation valve to be paired
with Reducing valve
3 bar Pressure
Reducing Valve
Isolation valve

14
Figure 11: Schematic installation diagram.
Balanced cold water draw-off
Combined Temperature and Pressure Relief valve with Expansion Relief Valve / Check Valve
0.3 Mpa/3 bar Pressure Reducing Valve and Strainer. (Stop cock can be fitted here)
MCWS to Kitchen (unbalanced cold mains supply)
Mains Cold Water Supply
KEY MCWS = Mains Cold Water Supply HWS = Hot Water Service SC = Stop Cock / Isolating Valve DOC = Drain Off Cock
Discharge pipe to atmosphere (see page 18 “Discharge Pipework”)
Isolating / Regulating Valves, as required
Mixed HWS supply
Balanced HWS and MCWS to bathrooms, showers, cloakrooms, etc
DOC DOC
DOC
DOC
SC
SC
Tundish
Mixing valve

15
Discharge
It is a requirement of Building Regulation G3 that any
discharge from an unvented system is conveyed to where
it is visible, but will not cause danger to persons in or about
the building. The tundish and discharge pipes should be
fitted in accordance with the requirements and guidance
notes of Building Regulation G3. The G3 Requirements
and Guidance section 3.50 - 3.63 are reproduced in the
following sections of this manual. For discharge pipe
arrangements not covered by G3 Guidance advice should
be sought from your local Building Control Officer. Any
discharge pipe connected to the pressure relief devices
(expansion valve and temperature/pressure relief valve)
must be installed in a continuously downward direction
and in a frost free environment.
Water may drip from the discharge pipe of the pressure
relief device. This pipe must be left open to the
atmosphere. The pressure relief device is to be operated
regularly to remove lime deposits and to verify that it is
not blocked.
G3 REQUIREMENT
“...there shall be precautions...to ensure that the hot
water discharged from safety devices is safely conveyed
to where it is visible but will not cause danger to persons
in or about the building.”
The following extract is taken from the latest G3
Regulations
Discharge pipes from safety devices
Discharge pipe D1
3.50 Each of the temperature relief valves or combined
temperature and pressure relief valves specified in 3.13
or 3.17 should discharge either directly or by way of
a manifold via a short length of metal pipe (D1) to a
tundish.
3.51 The diameter of discharge pipe (D1) should be not
less than the nominal outlet size of the temperature relief
valve.
3.52 Where a manifold is used it should be sized to accept
and discharge the total discharge from the discharge
pipes connected to it.
3.53 Where valves other than the temperature and
pressure relief valve from a single unvented hot water
system discharge by way of the same manifold that is
used by the safety devices, the manifold should be
factory fitted as part of the hot water storage system unit
or package.
Tundish
3.54 The tundish should be vertical, located in the same
space as the unvented hot water storage system and be
fitted as close as possible to, and lower than, the valve,
with no more than 600mm of pipe between the valve
outlet and the tundish (see fig 12).
Note: To comply with the Water Supply (Water Fittings)
Regulations, the tundish should incorporate a suitable air
gap.
3.55 Any discharge should be visible at the tundish. In
addition, where discharges from safety devices may not
be apparent, e.g. in dwellings occupied by people with
impaired vision or mobility, consideration should be given
to the installation of a suitable safety device to warn
when discharge takes place, e.g. electronically operated.
Discharge pipe D2
3.56 The discharge pipe (D2) from the tundish should:
(a) have a vertical section of pipe at least 300mm long
below the tundish before any elbows or bends in the
pipework (see fig. 12 page 17); and
(b) be installed with a continuous fall thereafter of at
least 1 in 200.
3.57 The discharge pipe (D2) should be made of:
(a) metal; or
(b) other material that has been demonstrated to be
capable of safely withstanding temperatures of the water
discharged and is clearly and permanently marked to
identify the product and performance standard (e.g. as
specified in the relevant part of BS 7291).
3.58 The discharge pipe (D2) should be at least one pipe
size larger than the nominal outlet size of the safety device
unless its total equivalent hydraulic resistance exceeds
that of a straight pipe 9m long, i.e. for discharge pipes
between 9m and 18m the equivalent resistance length
should be at least two sizes larger than the nominal
outlet size of the safety device; between 18 and 27m at
least 3 sizes larger, and so on; bends must be taken into
account in calculating the flow resistance. See Fig 12,
Table 4 and the worked example.
Note: An alternative approach for sizing discharge
pipes would be to follow Annex D, section D.2 of BS
6700:2006 Specification for design, installation, testing
and maintenance of services supplying water for domestic
use within buildings and their curtilages.
3.59 Where a single common discharge pipe serves more
than one system, it should be at least one pipe size larger
than the largest individual discharge pipe (D2) to be
connected.
3.60 The discharge pipe should not be connected to a
soil discharge stack unless it can be demonstrated that
the soil discharge stack is capable of safely withstanding
temperatures of the water discharged, in which case, it
should:
(a) contain a mechanical seal, not incorporating a water
trap, which allows water into the branch pipe without
allowing foul air from the drain to be ventilated through
the tundish;
(b) be a separate branch pipe with no sanitary
appliances connected to it;

16
(c) if plastic pipes are used as branch pipes carrying
discharge from a safety device they should be either
polybutylene (PB) to Class S of BS 7291-2:2006 or cross
linked polyethylene (PE-X) to Class S of BS 7291-3:2006;
and
(d) be continuously marked with a warning that no
sanitary appliances should be connected to the pipe.
Note:
1. Plastic pipes should be joined and assembled with
fittings appropriate to the circumstances in which they
are used as set out in BS EN ISO 1043-1.
2. Where pipes cannot be connected to the stack it
may be possible to route a dedicated pipe alongside or in
close proximity to the discharge stack.
Termination of discharge pipe
3.61 The discharge pipe (D2) from the tundish should
terminate in a safe place where there is no risk to persons
in the vicinity of the discharge.
3.62 Examples of acceptable discharge arrangements
are:
(a) to a trapped gully with the end of the pipe below a
fixed grating and above the water seal;
(b) downward discharges at low level; i.e. up to
100mm above external surfaces such as car parks, hard
standings, grassed areas etc. are acceptable providing
that a wire cage or similar guard is positioned to prevent
contact, whilst maintaining visibility; and
(c) discharges at high level: e.g. into a metal hopper
and metal downpipe with the end of the discharge pipe
clearly visible or onto a roof capable of withstanding high
temperature discharges of water and 3m from any plastic
guttering system that would collect such discharges.
3.63 The discharge would consist of high temperature
water and steam. Asphalt, roofing felt and non-metallic
rainwater goods may be damaged by such discharges.
Worked example of discharge pipe sizing
Fig. 12: shows a G1/2 temperature relief valve with a
discharge pipe (D2) having 4 No. elbows and length of
7m from the tundish to the point of discharge.
From Table 4 page 17:
Maximum resistance allowed for a straight length of
22mm copper discharge pipe (D2) from a G1/2
temperature relief valve is 9.0m.
Subtract the resistance for 4 No. 22mm elbows at 0.8m
each = 3.2m
Therefore the permitted length equates to: 5.8m
5.8m is less than the actual length of 7m therefore
calculate the next largest size.
Maximum resistance allowed for a straight length of
28mm pipe (D2) from a G1/2 temperature relief valves
equates to 18m.
Subtract the resistance of 4 No. 28mm elbows at 1.0m
each = 4.0m
Therefore the maximum permitted length equates to:
14m
As the actual length is 7m, a 28mm (D2) copper pipe will
be satisfactory.

17
Valve Outlet
Size
Minimum Size Of
Discharge Pipe D1
Minimum Size Of
Discharge Pipe D2 From
Tundish
Maximum Resistance
Allowed, Expressed As A
Length Of Straight Pipe (I.E.
No Elbows Or Bends)
Resistance Created
By Each Elbow Or
Bend
G1/2 15mm
22mm
28mm
35mm
up to 9m
up to 18m
up to 27m
0.8m
1.0m
1.4m
G3/4 22mm
28mm
35mm
42mm
up to 9m
up to 18m
up to 27m
1.0m
1.4m
1.7m
G1 28mm
35mm
42mm
54mm
up to 9m
up to 18m
up to 27m
1.4m
1.7m
2.3m
Table 4: Sizing of copper discharge pipe (D2) for common temperature relief valve outlet sizes
Safety device
(e.g. Temperature
relief valve) Metal discharge pipe (D1) from
Temperature relief valve to tundish
Tundish
Discharge below
fixed grating
(Building Regulation
G3 section 3.61 gives
alternative points
of discharge)
Fixed grating
Trapped
gully
600mm maximum
300mm
minimum
Discharge pipe (D2) from tundish,
with continuous fall. See Building
Regulation G3 section 3.56,
Table 1 and worked example
Figure 12: Typical discharge pipe arrangement (extract from Building Regulation G3 Guidance Section 3.50)
Notes:
1) Discharge pipe-work D2 can now be a plastic pipe but only pipes that have been tested to a minimum 110°C
must be used.
2) Discharge pipe D2 can now be plumbed in the soil stack but only soil stacks that can handle temperatures of
99°C or greater should be used.

18
6.3 Electrical connections
In case of difficulty contact service support; contact
details are available on page 36 of this booklet.
WARNING
`Disconnect from the mains electrical
supply before removing any covers.
`Never attempt to replace the immersion
heater(s) other than with genuine
manufacturers components. Using
other manufacturers components may
invalidate the warranty on the cylinder.
`DO NOT bypass the thermal cut-out(s) in
any circumstances. All electrical wiring
should be carried out by a competent
electrician and be in accordance with the
latest I.E.E Wiring Regulations.
`Each circuit must be protected by a
suitable fuse and double pole isolating
switch with a contact separation of at
least 3mm in both poles.
`DO NOT operate the immersion heaters
until the appliance has been filled with
water.
Space and heating systems controls
`The controls provided with the cylinder will ensure
the safe operation of the unit within the central
heating system.
`Connections to the various system components is
made via the wiring centre fitted to the front of the
cylinder and the terminal identification labels within
the wiring centre to aid in connecting the various
external system components such as the mains
supply, programmer and boiler.
Back up immersion heater
`The back up immersion heater should be wired in
accordance with fig 14 and 15, page 19.
`The immersion heater thermostat is factory set at
57oC. This is set for eco mode, To maximise water
availability the thermostat should be set to maximum
during commissioning (see Fig 16 page 19). Should
this require adjustment see Fig 16 for details of how
to adjust the temperature setting. Each immersion
heater has its own individual thermostatic control.
The thermostat incorporates a thermal cut-out that
will switch off the immersion heater in the event of a
thermostat failure. The thermal cut-out reset button
position is also shown on Fig 16.
LIFT OFF
REPLACE
LIFT FROM THIS POINT
LUGS
Access to Control Unit:
Disconnect from mains supply before removing any
covers.
Removing the Control Cover.
`Unscrew the large screw using a flat ended screw
driver.
`Lift from bottom of cover at point indicated until
cover comes away freely.
Replacing the Control Cover:
`Tilt and align the top 2 lugs in the holes indicated.
`Firmly press the cover until it "snaps" back in place.
`Tighten the large screw.
WARNING
`Do not over tighten
Figure 13: Cover Access

19
WARNING
Should the Megaflo be used in conjunction
with a boiler or external controls that
control the water temperature via a sensor
connected to the cylinder, it should be noted
that the factory fitted indirect thermostat and
thermal cut-out MUST NOT be disconnected
or bypassed. To do so would invalidate the
product approvals and warranty and it
would not comply with Building Regulations.
Should this method of control be adopted
the Megaflo Indirect thermostat should be
set at maximum and the cylinder control
temperature set at 68oC to avoid the
thermostat over-riding the boiler control.
Where the boiler or external controls do not
directly power the 2 Port Motorised Valve
supplied with the Megaflo, the wiring should
ensure that in the event of the thermal
cut-out on the Megaflo Indirect controls
operating power will be interrupted to the 2
Port Motorised Valve such that it closes and
prevents flow of the primary heating fluid
around the Megaflo primary heat exchanger
coil.
For further details of wiring the boiler, or
external controls consult the manufacturer’s
installation instructions.
Figure 15: Direct wiring schematic
Figure 14: Indirect wiring schematic
LN
1 2 3
Control Housing Details
Immersion connections
1.5mm² 3 Core HO5 VV-F
sheathed cable
Indirect control wiring
NL
1.5mm² 3 Core
HO5 VV-F sheathed
cable
Immersion
heater
connections
6.4 Filling the appliance
`Ensure the drain cock is CLOSED.
`Open a hot tap furthest from the cylinder.
`Open the isolating valve on the 3 bar Pressure
Reducing Valve by turning the blue handle on the
stop cock (if fitted in this position) so that it lies
parallel to the direction of flow. Open the mains stop
cock to fill the unit. When water discharges from the
tap, allow to run for a few minutes to thoroughly
flush through any residue, dirt or swarf, then close
the tap.
`Open successive hot taps to purge the system of air.
SPINDLE POSITIONS
= MINIMUM TEMP
= MAXIMUM TEMP
= APPROX 60 °C
A
ROTATE SPINDLE CLOCKWISE
FOR TEMPER ATURE INCREASE
AND COUNTER CLOCKWISE
FOR TEMPER TURE DECREASE
TEMPERATURE ADJUSTING
SPINDLE
THERMAL CUT-OUT RESET BUTTON
Figure 16: Boiler and Immersion controls

20
WARNING
`If the unit is to be left unused following
installation and commissioning e.g.
unoccupied properties, the water heater
should be drained or regularly flushed
through with fresh mains water once a
week.
`When placing the unit into service, the
procedure for filling the unit and the
system checks above should be observed.
7.2 Checklist before commissioning
`Check all water connections for leaks and rectify as
necessary.
`Turn off mains water supply.
`Remove the pressure reducing valve head work to
access the strainer mesh, clean and re-fit.
`Turn the water supply back on.
`Manually open, for a few seconds, each Relief Valve
in turn, checking that water is discharged and runs
freely through the tundish and out at the discharge
point.
`Ensure that the valve(s) re-seat satisfactorily.
7.3 Commissioning procedure
Indirect units
`Ensure the filling loop hose is connected at both ends
and is tight.
`Fill the indirect (primary) circuit following the boiler
manufacturer’s commissioning instructions.
`Open the isolating valves at either end of the filling
loop and allow to fill from the mains inlet supply.
`To ensure the appliance primary heat exchanger is
filled, both of the 2 port motorised valves (supplied)
should be manually opened by moving the lever on
the motor housing to the MANUAL setting. When
the primary circuit is full return the lever to the
AUTOMATIC position.
`Air can be vented from the primary heating coil by
unscrewing the small dust cap on the auto air vent
by half a turn.
`The primary system should be pressurised to the
minimum pressure required by the boiler (usually 1
bar), the pressure gauge fitted should be used to
ensure the correct system pressure is set.
`When full and pressurised, the filling loop isolating
valves should be closed, the pipe disconnected and
the caps replaced. The levers on the motorised valves
should be returned to the Auto position.
`Check primary circuit for leaks and rectify as necessary
Switch on the boiler, ensure the programmer is set to
Hot Water and allow the cylinder to heat up to a
normal working temperature (70oC recommended).
7. Commissioning
7.1 General
After filling the installation with water in the previous
section please follow the following steps to complete the
installation of the unit.
WARNING
DO NOT operate the immersion heaters or
primary circuit until the appliance has been
filled with water.
Direct Heating
`Switch on electrical supply to the immersion heater
and allow the appliance to heat up to normal working
temperature, factory set to 57°C but for maximum
water availability reset to 70°C (see Fig 16 page 19).
`The adjustment represents a temperature range of
10°C to 70°C.
`Check the operation of thermostat and that no
water has issued from the Expansion Relief Valve or
Temperature/Pressure Relief Valve during the heating
cycle.
Benchmark
The cylinder is covered by the Benchmark Scheme
which aims to improve the standards of installation
and commissioning of domestic heating and hot water
systems in the UK and to encourage regular servicing to
optimise safety, efficiency and performance.
Benchmark is managed and promoted by the Heating
and Hotwater Industry Council. For more information
visit www.centralheating.co.uk.
All installations must be notified to Local Area Building
Control either directly or through a Competent Persons
Scheme. A Building Regulations Compliance Certificate
will then be issued to the customer who should, on
receipt, write the Notification Number on the Benchmark
Checklist.
This product should be serviced regularly to optimise its
safety, efficiency and performance. The service engineer
should complete the relevant Service Record on the
Benchmark Checklist after each service.
The Benchmark Checklist may be required in the event of
any warranty work.