Heatrae Sadia MegaFlo User manual

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36005823 issue 6

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Contents
SECTION PAGE
1 INTRODUCTION ............................................................................ 3
2 GENERAL REQUIREMENTS......................................................... 4
3 INSTALLATION - GENERAL........................................................... 7
4 INSTALLATION - DIRECT UNITS................................................... 16
5 INSTALLATION - INDIRECT UNITS............................................... 18
6 COMMISSIONING.......................................................................... 23
7 USER INSTRUCTIONS .................................................................. 25
8 MAINTENANCE.............................................................................. 27
9 FAULT FINDING & SERVICING ..................................................... 29
10 DIMENSIONS & SPECIFICATIONS ............................................... 32
11 GUARANTEE.................................................................................. 35
12 CONTACTS .................................................................................... 36
.......................................................................
Contents
Please read and understand these instructions before starting work.
Please leave this leaet with the user following installation

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Congratulations on your purchase of a Heatrae Sadia Megao High Efciency un-
vented water heater. The Megao is manufactured in the UK from top quality materials
and meets all the latest relevant safety and constructional standards. The high grade
Duplex stainless steel cylinder offers exceptional strength and corrosion resistance
which is backed by a 25 year guarantee. Its performance and insulation levels exceed
the latest requirements of Building Regulation Part L.
The Megao unvented water heater can be fed directly from the cold water mains
supply to the property without the need for separate feed cisterns or vent pipes. It is
supplied complete with all its necessary inlet and safety controls, electric immersion
heater(s) and, for indirect units, a cylinder thermostat, thermal cut-out, 2-port motor-
ised valve and wiring centre.
Generally its pressure and owrate performance will far exceed that from a compara-
ble vented system, thermal store, multipoint instantaneous gas heater or combination
boiler.
The Megao requires no separate expansion vessel as any expanded water is
accommodated within an internal air volume.
Introduction
Introduction
Figure 1 - Schematic installation details
COLD WATER
COMBINATION
VALVE
BALANCED
COLD WATER
CONNECTION
(IF REQUIRED)
T&P RELIEF
VALVE
ELEMENT /
CONTROLS
HOUSING
PRIMARY
RETURN
PRIMARY
FLOW
INLET
DRAIN COCK DISCHARGE
PIPE
TUNDISH
SECONDARY RETURN
TAPPING (IF REQUIRED)
TO HOT
OUTLETS
MAINS
WATER
SUPPLY
EXPANSION VALVE
CORE UNIT

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IMPORTANT : PLEASE READ AND UNDERSTAND THESE INSTRUCTIONS BEFORE INSTALLING
THE MEGAFLO WATER HEATER. INCORRECT INSTALLATION MAY INVALIDATE GUARANTEE.
THIS APPLIANCE IS NOT INTENDED FOR USE BY PERSONS (INCLUDING CHILDREN) WITH
REDUCED PHYSICAL, SENSORY OR MENTAL CAPABILITIES, OR LACK OF KNOWLEDGE
AND EXPERIENCE, UNLESS THEY HAVE BEEN GIVEN SUPERVISION OR INSTRUCTION
CONCERNING THE USE OF THE APPLIANCE BY A PERSON RESPONSIBLE FOR THEIR
SAFETY.
THE MEGAFLO MUST BE INSTALLED (SECTIONS 2 - 5), COMMISSIONED (SECTION 6)
AND MAINTAINED (SECTIONS 8 - 10) BY A COMPETENT 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). FOLLOWING
INSTALLATION AND COMMISSIONING, THE OPERATION OF THE HEATER SHOULD BE
EXPLAINED TO THE USER (SECTION 7) AND THESE INSTRUCTIONS LEFT WITH THEM FOR
FUTURE REFERENCE.
2.1 COMPONENT CHECK LIST
Before commencing installation check that all the components for your Megao unit are con-
tained in the package. The following components are supplied as standard with your Megao
unit :
• Factory tted immersion heater (s) and thermal controls
• Cold Water Combination Valve (comprises Isolating Valve, Pressure Reducing Valve,
Strainer, and Check Valve)
• Expansion Core Unit (comprises Check Valve and Expansion Valve)
• Factory tted Temperature/Pressure Relief Valve (set at 90oC/1 Mpa (10bar))
• Tundish (included in Cold Water Combination Valve pack)
• Factory tted Indirect Thermostat and Thermal Cut-out (CL units only)
• T&P Relief Valve Insulation Set
• Drain Valve
• Wiring Centre (CL units only)
• 2-Port Motorised Valve (CL units only)
• Lifting handle
2.2 SITING THE MEGAFLO (see Figure 1)
The Megao unit must be vertically oor mounted. It can be placed anywhere convenient
provided the discharge pipe(s) from its safety valves can be correctly installed. Areas that are
subject to freezing must be avoided. Ensure that the oor is of sufcient strength to support
the “full” weight of the unit (refer to Tables 4 and 5 on page 33 for unit weights). Pipe runs
should be kept as short as possible for maximum economy. Access to associated controls,
2General Requirements
General Requirements

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immersion heaters and indirect controls should be possible for servicing and maintenance of
the system (Note: indirect controls housing hinges open to the left hand side).
Please do not install valves or pipework (except discharge pipe) within 50mm (2”) of the
T&P relief valve to allow your insulation set to be tted. The insulation set is important to
ensure heat and energy conservation. See section 3.8 for more information.
To aid installation the Megao is provided with lifting points located in the base moulding
and a lifting handle. The lifting handle should be fully threaded onto the outlet boss before
use. Once the Megao is suitably positioned the lifting handle should be removed to allow
connection of the outlet pipework. The weights of the units are noted on the tables on page
33.
2.3 WATER SUPPLY
Bear in mind that the mains water supply to the property will be supplying both the hot
and cold water requirements simultaneously. It is recommended that the maximum water
demand be assessed and the water supply checked to ensure this demand can be met.
NOTE: A high mains water pressure will not always guarantee high ow rates.
Wherever possible the main supply pipe should be in 22mm. The minimum mains water
supply requirements should be 0.15 MPa (1.5 bar) working pressure and 20 litres per min-
ute owrate. At these values outlet owrates may be poor if several outlets are used simulta-
neously, the higher the available pressure and owrate the better the system performance
will be.
The Megao has an operating pressure of 3 bar which is controlled by the Cold Water Com-
bination Valve. The Cold Water Combination Valve can be connected to a maximum mains
supply pressure of 1.6 MPa (16 bar). The water supply must be of wholesome water quality
(Fluid Category 1 as dened by the Water Supply Regulations 1999).
2.4 OUTLET/TERMINAL FITTINGS (TAPS, ETC.)
The Megao can be used in conjunction with most types of terminal ttings. It is advanta-
geous in many mixer showers to have balanced hot and cold water supplies, in these
instances the balanced cold water supply should be teed off the supply to the Megao im-
mediately after the Cold Water Combination Valve (see Figures 4 and 5). Branches to cold
drinking outlets should be taken before the valve.
Outlets situated higher than the Megao unit will give outlet pressures lower than that at
the heater, a 10m height difference will result in a 0.1 Mpa (1 bar) pressure reduction at the
outlet tting.
NOTE: Accessories should have a rated operating pressure of at least 0.8 MPa (8 bar).

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General Requirements
2.5 LIMITATIONS
The Megao unvented water heater should not be used in any of the following instances:
• Solid fuel boilers or any other boiler in which the energy input is not under effective ther
mostatic control unless additional and appropriate safety measures are installed.
• Gravity circulation primaries.
• Steam heating plant unless additional and appropriate safety devices are installed.
• Ascending spray type bidets or any other Class 5 back syphonage risk requiring that a
Type AA, AB, AD or AG air gap be employed.
• 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.
• Areas where the water consistently contains a high proportion of solids, eg. suspended
matter that could block the strainer, unless adequate ltration can be ensured.
•The installation must be carried out in accordance with the relevant requirements of:
• The appropriate Building Regulations: either The Building Regulations (England), The
Building Regulations (Scotland) or Building Regulations (Northern Ireland).
• The Water Fittings Regulations (England and Wales) or Water Byelaws (Scotland).

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3.1 PIPE FITTINGS
All pipe connections to the Megao are made via 22mm compression ttings directly to
the unit (nuts and olives supplied). The ttings are also threaded 3/4” BSP male parallel
should threaded pipe connections be required.
3.2 COLD WATER SUPPLY
A 22mm cold water supply is recommended, however, if a 15mm (1/2”) supply exists
which provides sufcient ow (see section 2.3) this may be used. More ow noise may
be experienced from small bore pipes due to the increased water velocity through them.
The Cold Water Combination Valve supplied with the Megao incorporates a full ow
isolating valve which will enable the Megao to be isolated from the mains supply for
maintenance or servicing. To close the valve the black handle should be turned so that
it lies at 90o to the direction of ow. To open turn the handle so that it lies parallel to the
direction of ow.
3.3 COLD WATER COMBINATION VALVE (see Figure 2)
The Cold Water Combination Valve can be connected anywhere on the cold water mains
supply prior to the Megao unit. There is no requirement to site it close to the unit, it can
be located at a point where the mains supply enters the premises if this is more conve-
nient. The Expansion Valve connection must not be used for any other purpose.
The Cold Water Combination Valve can be installed as a complete one-piece unit. The
valve incorporates a factory set, non-adjustable Pressure Reducer/Strainer, an Expan-
sion Valve connection and a single Check Valve. The valve can be tted in any orienta-
tion to suit the installation, however, ensure that the Valve is installed with the direction of
ow arrows (stamped on the side of the brass body) pointing towards the Megao heater.
Should you wish to site the Expansion Valve on the Cold Water Combination Valve this
can be done by unscrewing the connection nut beneath the Expansion Valve on the
Expansion Core Unit and removing the Expansion Valve. The connecting nut and blank-
ing plug should then be unscrewed from the Cold Water Combination Valve and replaced
with the Expansion Valve. Note: if the Expansion Valve is tted to the Cold Water Combi-
nation Valve the Expansion Core Unit should not be used as the Check Valve within it will
prevent free passage of expanded water to the Expansion Valve. Ensure the discharge
from the Expansion Valve can be correctly installed.
If a balanced pressure cold water supply is required to a thermostatic shower mixer valve
this may be teed off the supply to the Megao immediately after the Cold Water Combi-
nation Valve (see Figure 4). Branches to drinking water outlets should be taken before
the valve to avoid the possibility of warm expanded water being drawn from the tap.
3.4 EXPANSION CORE UNIT (see Figure 3)
Should a balanced pressure cold water supply be required for other cold water outlets
the Expansion Core Unit supplied should be used. The Core Unit should be tted into
the pipework between the Cold Water Combination Valve and the Megao (note direc-
tion of ow arrows). The cold water balanced draw off connection should be taken from
Installation - General
Installation - General

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Installation - General
Figure 2 - Cold Water Combination Valve
Figure 3 - Expansion Core Unit
between the Cold Water Combination Valve and the Expansion Core Unit (see Figure 5). The
Expansion Valve connection on the Cold Water Combination Valve should remain blanked off
using the blanking nut and seal provided. Ensure the discharge from the Expansion Valve can
be correctly installed.
ISOLATING VALVE
MAINS IN
22MM
COMPRESSION
CONNECTION
PRESSURE REDUCING
VALVE HOUSING
PRESSURE REDUCING
VALVE CARTRIDGE
(3 BAR)
22MM
COMPRESSION
CONNECTION
OUTLET TO
MEGAFLO
EXPANSION VALVE
CONNECTION (IF
ONE-PIECE VALVE
IS REQUIRED)
TAKE NOTE OF
FLOW DIRECTION
EXPANSION RELIEF VALVE
DISCHARGE CONNECTION
EXPANSION RELIEF VALVE
FROM COLD
WATER
COMBINATION
VALVE
OUTLET TO
MEGAFLO
22MM COMPRESSION
CONNECTION
EXPANSION CORE UNIT
(INCORPORATES
CHECK VALVE)
MOUNTING NUT 22MM COMPRESSION
CONNECTION
TAKE NOTE OF
FLOW DIRECTION

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Figure 4 - Schematic installation diagram using Cold Water Combination Valve
Tundish
Megaflo HE
Discharge pipe to atmosphere
(See Section 3.9 “Discharge
Pipework“)
KEY MCWS Mains cold water supply
HWS Hot water service SC Stop Cock DOC Drain Off Cock
Temperature/Pressure
Relief Valve
Balanced cold water
draw off to shower mixer valves (Note: tapping must be min 3m from Megaflo inlet connection)
Balanced HWS and MCWS to each shower.
Isolating/Regulating
Valves as required
HWS supply
SC
SC
DOC
Incoming Cold
Water Main
MCWS to Kitchen and drinking water outlets (unbalanced cold mains supply)
DOC DOC DOC
Cold Water Combination
Valve incorporating
Pressure Reducing Valve,
Check Valve and Expansion Relief Valve
Isolating Valve, Strainer,

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Installation - General
Figure 5 - Schematic installation diagram using Cold Water Combination Valve in conjunction
with Expansion Core Unit
Tundish
Megaflo HE
Discharge pipe to atmosphere
(See Section 3.9 “Discharge
Pipework“)
KEY MCWS Mains cold water supply
HWS Hot water service SC Stop Cock DOC Drain Off Cock
Temperature/Pressure
Relief Valve
Balanced cold water
draw off
Balanced HWS and MCWS to bathrooms, showers,cloakrooms,
etc.
Isolating/Regulating
Valves as required
HWS supply
Expansion Core Unit (combined
Expansion Relief
Valve/Check Valve)
SC
SC
DOC
Incoming Cold
Water Main
MCWS to Kitchen (unbalanced cold
mains supply)
DOC DOC DOC
Cold Water Combination
Valve incorporating
Pressure Reducing Valve,
and Check Valve
NB Expansion Valve
tapping must be blanked
off
Isolating Valve, Strainer

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3.5 DRAIN TAP
A draining tap is supplied and should be installed in the cold water supply to the Megao
unit between the Cold Water Combination Valve (or Expansion Core Unit if being used)
and the heater at as low a level as possible (see Figure 1). It is recommended that the
outlet point of the drain pipe work be at least 1 metre below the level of the heater (this
can be achieved by attaching a hose pipe to the drain tap outlet spigot). The draining tap
supplied provides very good water ow control and blanking cap for extra security.
3.6 OUTLET PIPEWORK
Ideally the pipework from the Megao to the outlet ttings should be in 22mm pipe with
short runs of 15mm pipe to showers and basin taps. Small bore pipe can also be used to
suit some taps, but runs should be of minimum length. Pipe sizes may vary due to system
3.7 SECONDARY CIRCULATION
If a secondary circulation system is required it is recommended that it be connected to
the Megao as shown in Figure 6 via a Swept Tee joint (not supplied - available as an ac-
cessory, order code no. 95 970 509). The secondary return pipe should be in 15mm pipe
and incorporate a check valve to prevent backow. A suitable WRAS approved bronze
circulation pump will be required. On large systems, due to the increase in system water
content, it may be necessary to t additional expansion volume to the system by tting an
external expansion vessel to the secondary circuit. This should be done if the capacity of
the secondary circuit exceeds 10 litres.
Pipe capacities (copper)
15mm o/d = 0.13 litres per metre run (10 litres = 77m)
22mm o/d = 0.38 litres per metre run (10 litres = 26m)
28mm o/d = 0.55 litres per metre run (10 litres = 18m)
Secondary circulation is NOT recommended for direct electric units being used on Off
Peak electricity tariffs.
3.8 T&P RELIEF VALVE INSULATION
A set of insulating components is supplied with the Megao water heater and should be
installed to gain maximum heat and energy saving benets. See Figure 7 for installation
instructions.
3.9 WARNINGS
i) Under no circumstances should the factory tted Temperature/Pressure Relief Valve
be removed other than by Authorised Heatrae Sadia personnel. To do so will invali-
date any guarantee or claim.

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Installation - General
Figure 6 - Secondary circulation connection
CHECK
COLD
COLD INLET
SECONDARY
SWEPT
SECONDARY
CIRCULATION
ii) The Cold Water Combination Valve must be tted to the mains water supply to the Megao unit.
iii) No control or safety valves should be tampered with.
iv) Water may drip from the discharge pipe of the pressure relief device (Expansion
Valve) and this pipe must be left open to atmosphere. The discharge pipe should not be blocked
or used for any other purpose.
Figure 7 - Installation of T&P insulation set
T&P RELIEF
VALVE
DISCHARGE
PIPEWORK
TO TUNDISH
'FEMALE'
INSULATING
PIECE
'MALE'
INSULATING
PIECE
DISCHARGE
PIPE
PLASTIC
COVER
CLIP
INTO
PLACE!
AB
CD

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3.10 DISCHARGE PIPEWORK
It is a requirement of Building Regulations 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 tted in accordance with the requirements and
guidance notes of Building Regulations. Building Regulation G3 Requirements and Guidance
section 3.9 are reproduced in the following sections.
Information Sheet No. 33 available from the British Board of Agrément gives further advice on
discharge pipe installation. For discharge pipe arrangements not covered by G3 Guidance or
BBA Info Sheet No.33 advice should be sought from your local Building Control Ofcer.
Any discharge pipe connected to the pressure relief devices (Expansion Valve and Tempera-
ture/Pressure Relief Valve) must be installed in a continuously downward direction and in a
frost free environment.
The water may drip from the discharge pipe of the pressure relief device and that 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.”
G3 GUIDANCE SECTION 3.9
The discharge pipe (D1) from the vessel up to and including the tundish is generally sup-
plied by the manufacturer of the hot water storage system. Where otherwise, the installation
should include the discharge pipe(s) (D1) from the safety device(s). In either case the tundish
should be vertical, located in the same space as the unvented hot water storage system and
be tted as close as possible and within 500mm of the safety device e.g. the temperature
relief valve.
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, preferably be of metal and:
a. 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. discharge
pipes between 9m and 18m 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 ow resistance. Refer to
Diagram 7, Table 1 and the worked example.
An alternative approach for sizing discharge pipes would be to follow BS 6700:1987 Specica-
tion for design, installation, testing and maintenance of services supplying water for domestic
use within buildings and their curtilages, Appendix E, section E2 and table 21.
b. have a vertical section of pipe at least 300mm long below the tundish before any elbows
or bends in the pipe work.
c. be installed with a continous fall, and in a frost free enviroment.

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Installation - General
d. have discharges visible at both the tundish and the nal point of discharge, but where this is not
possible or is practically difcullt there should be clear visibilty at one or other of these locations.
Examples of acceptable discharge arrangements are:
i. ideally below a xed grating and above the water seal in a trapped gully.
ii. 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 where children may play or
otherwise come into contact with discharges a wire cage or similar guard is positioned to prevent
contact, whilst maintaining visibility.
iii. discharges at high level; e.g. into a metal hopper and metal down pipe with the end of the
discharge pipe clearly visible (tundish visible or not) or onto a roof capable of withstanding high
temperature discharges of water and 3m from any plastics guttering system that would collect
such discharges (tundish visible).
iv. where a single pipe serves a number of discharges, such as in blocks of ats, the number
served should be limited to not more than 6 systems so that any instalation discharging can be
traced reasonably easily. The single common discharge pipe should be at least one pipe size larger
than the largest individual discharge pipe (D2) to be connected. If unvented hot water storage
systems are installed where discharges from safety devices may not be apparent i.e. in dwellings
occupied by blind, inrm or disabled people, consideration should be given to the installation of
an electronically operated device to warn when discharge takes place.
Note: The discharge will consist of scalding water and steam. Asphalt, roong felt and non-metallic
rainwater goods may be damaged by such discharges.
Worked example of discharge pipe sizing
The example below is for 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 1:
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 valve 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.

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Table 1 - Sizing of copper discharge pipe (D2) for common T&P relief valve sizes
Figure 8 - Schematic discharge pipe arrangement
VALVE OUTLET
SIZE
MINIMUM SIZE OF
DISCHARGE PIPE D1
MINIMUM SIZE OF
DISCHARGE PIPE D2
FROM TUNDISH
MAXIMUM RESISTANCE
ALLOWED, EXPRESSED
AS A LENTGH OF
STRAIGHT PIPE (I.E. NO
ELBOWS OR BENDS
RESISTANCE CREATED BY
EACH ELBOW OR BEND
G 1/2 15MM 22mm
28mm
35mm
UP TO 9M
UP TO 18M
UP TO 27M
0.8M
1.0M
1.4M
G 3/4 22MM 28mm
35mm
42mm
UP TO 9M
UP TO 18M
UP TO 27M
1.0M
1.4M
1.7M
G 1 28MM 35mm
42mm
54mm
UP TO 9M
UP TO 18M
UP TO 27M
1.4M
1.7M
2.3M
Fixed grating
Discharge below
fixed grating
(Building Regulation
G3 section 3.9d gives
alternative points
of discharge)
Trapped
gully
Discharge pipe (D2) from tundish,
with continuous fall. See Building
Regulation G3 section 3.9d i-iv,
Table 4 and worked example
300mm
minimum
500mm maximum
Metal discharge pipe (D1) from
Temperature relief valve to tundish
Tundish
Safety device
(e.g. Temperature
relief valve)

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4.1 IMMERSION HEATER(S)
The Megao is supplied with either one (D models), two (DD models) or three (DDD models)
factory tted immersion heaters. Each immersion heater is rated 3kW at 240V.
The DDD models are supplied with three immersion heaters and a blanking plug tted to the
uppermost of the three lower immersion heater bosses. Should a different combination be
required the blanking plug and the upper (boost) immersion heater can be swapped.
To remove the blanking plug:
Ensure the cylinder is drained of water rst. Open the cover to the uppermost of the three lower
immersion heater bosses. The cover is secured by a cross-headed screw. Unscrew brass
backnut using the key spanner provided with the unit. Remove the blanking plate and sealing
gasket from the boss.
To remove the immersion heater:
Open the cover to the upper immersion heater. Unplug the thermostat from the element by gen-
tly pulling the thermostat outwards. Unscrew the brass backnut using the key spanner provided.
Remove the immersion heater assembly and sealing gasket from the boss.
Replacement:
Insert the immersion heater and sealing gasket into the required boss. Ensure that the sealing
gasket is not displaced when inserting. It may be helpful to support the immersion heater using
a round bladed screwdriver inserted into one of the thermostat pockets. Hand tighten the brass
backnut. Secure the immersion heater in position by tightening with the key spanner provided.
Insert the blanking plate into the remaining boss ensuring the sealing gasket is not displaced
when inserting. Hand tighten the brass backnut. Secure in position by tightening with the key
spanner provided.
If an additional immersion heater is required order part no. 95 970 510.
4.2 WIRING (see Figure 8)
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.
The immersion heater(s) should be wired in accordance with Diagram 9. The immersion heat-
ers MUST be earthed. The supply cable should be 1.5mm2 3 core HOFR sheathed and must
be routed through the cable gland provided with the outer sheath of the cable rmly secured by
tightening the screw on the cable gland. Replace the immersion heater cover(s) before operat-
ing ensuring that the threaded edge clip is in position to provide a suitable thread for the cover
screw.
DO NOT OPERATE THE IMMERSION HEATER(S) UNTIL THE MEGAFLO HAS BEEN
FILLED WITH WATER.
4Installation - Direct units
Installation - Direct units

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4.3 OPERATION
It is recommended that the immersion heater thermostats are set to between position 4
and 5 (60o- 65oC), however they can be set between 1 and 5 (10o and 70oC). The thermo-
stat 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 indicated on Figure 10.
DO NOT bypass the thermal cut-out in any circumstances.
4.4 SAFETY
DO NOT BYPASS THE THERMAL CUT-OUT(S) IN ANY CIRCUMSTANCES
DISCONNECT FROM THE MAINS SUPPLY BEFORE REMOVING ANY COVERS
NEVER ATTEMPT TO REPLACE AN IMMERSION HEATER OTHER THAN WITH THE REC-
OMMENDED HEATRAE SADIA MEGAFLO SPARE PART
Figure 9 -
Schematic wiring
diagram - Direct
immersion
heaters THERMOSTAT
EARTH
CONNECTION
FUSED (13A) DOUBLE
POLE ISOLATING
SWITCH
1.5mm23 CORE
HOFR SHEATHED
CABLE
Figure 10 - Immersion heater details
THERMAL CUT-OUT
RESET BUTTON
ELECTRICAL
TERMINATIONS
CUSTOMER
EARTHING
TERMINAL
CABLE GLAND
NOTE:FOR CLARITY THE EARTH LINK WIRE BETWEEN CUSTOMER EARTHING
TERMINAL AND EARTHING TAG NOT SHOWN.THIS MUST NOT BE REMOVED!
EARTHING TAG
THERMOSTAT
ADJUSTMENT
THERMOSTAT
THREADED EDGE CLIP

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5.1 BOILER SELECTION
The Megao Indirect (CL) models are suitable for use with most gas or oil red boilers compat-
ible with unvented systems i.e. tted with a temperature control thermostat and thermal cut-out.
If in doubt consult the boiler manufacturer.
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, should NOT be used.
The boiler used can either be a sealed system or open vented type, maximum primary circuit
pressure 3 bar.
The primary ow 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 an air bleed point or auto-
matic air vent is incorporated in the primary return pipework close to the Megao unit.
The boiler ow temperature should usually be set to 82oC (maximum ow temperature to
primary heat exchanger 90oC).
The boiler cannot be vented through the Megao unit.
5.2 INDIRECT THERMAL CUT-OUT AND 2-PORT MOTORISED VALVE
To comply with Building Regulations and to prevent the Megao from overheating the 2-port
motorised valve supplied MUST be tted to the primary ow to the indirect coil (see Figure 11).
5.3 WIRING
All electrical wiring should be carried out by a competent electrician and be in accordance with
the latest I.E.E. Wiring Regulations.
The Megao Indirect Thermostat and Thermal Cut-Out are factory pre-wired. The 2-port
motorised valve supplied MUST be wired in series with the Indirect controls such that the power
supply to the valve is interrupted should either the Thermostat or Thermal Cut-Out operate. The
Figures 13 or 14 detail the wiring required between these controls and the motorised valve. Wir-
ing to external controls is made via the terminal block tted. The cable should be routed through
the aperture in the terminal cover and secured using the cable grip provided. The Indirect
Thermal Cut-out MUST NOT be bypassed.
5.4 HEATING SYSTEM CONTROLS
The controls provided with the Megao will ensure the safe operation of the Megao within
a central heating system. Other controls will be necessary to control the space heating
requirements and times that the system is required to function. Depending on the boiler
selected, heating circuit design and controls used it may be benecial to incorporate a system
bypass in the heating system pipework.
The Megao is compatible with most heating controls, examples of electrical circuits are
given in Diagrams 13 and 14. However, other systems may be suitable, refer to the controls
manufacturers’ instructions, supplied with the controls selected, for alternative system wiring
schemes.
5Installation - Indirect units
Installation - Indirect units

Megaflo He
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5.5 IMMERSION HEATER(S)
The Megao indirect units (CL models) are supplied with an immersion heater which can
be used as an alternative heat source should the boiler supply need to be isolated from the
Megao unit. The immersion heater is located within the controls housing. Refer to Sec-
tions 4.2 and 4.3 and Diagram 9 for details of wiring and operation of the immersion heater.
210 litre models and above are supplied with a second blanked off boss which can be used
for the connection of a second immersion heater should this be required.
To remove the blanking plug:
Ensure the cylinder is drained of water rst. Open the cover to the upper immersion heater
boss. Unscrew the brass backnut using the key spanner provided with the unit. Remove
the blanking plate and sealing gasket from the boss.
Fitting additional immersion heater:
Insert the immersion heater and sealing gasket into the upper boss. Ensure that the
sealing gasket is not displaced when inserting. It may be helpful to support the immersion
heater using a round bladed screwdriver inserted into one of the thermostat pockets. Hand
tighten the brass backnut. Secure the immersion heater in position by tightening with the
key spanner provided.
Figure 11 - Primary connections to indirect (CL) units
PRIMARY
RETURN
PRIMARY
FLOW
TO HOT
OUTLETS
AIR
VENT
2 PORT MOTORISED
VALVE (SUPPLIED)
INLET

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20
CABLE CLAMPS TERMINAL BLOCK
INDIRECT
THERMOSTAT
THERMOSTAT
ADJUSTMENT
INDIRECT
THERMAL
CUT-OUT
INDIRECT THERMAL
CUT-OUT RESET
BUTTON
NOTE:
THE HOUSING COVER AND ELEMENT ASSEMBLY HAVE BEEN REMOVED FROM
THIS VIEW FOR CLARITY
Figure 12 - Indirect controls housing details
Installation - Indirect units