MCDonald MULTIflow User manual

Technical Manual
MULTIflow
Thermal Store Cylinders
Tel: [phone]
www.mcdonaldwaterstorage.com
January 2021
MULTI flow Thermal Store Tank Technical Manual
Manual must be completed by Installer and left with Home Owner

Issue 3 13/01/21
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Contents
Preface.................................................................................................................2
Handling & Storage..............................................................................................3
What is a Thermal Store? ....................................................................................3
Design ..................................................................................................................4
Mains Water Supply ............................................................................................5
Immersion Heaters ..............................................................................................5
Water Treatment.................................................................................................6
Pipework..............................................................................................................7
Discharge/Overflow Requirements .....................................................................7
Showers ...............................................................................................................8
MULTIflow OV: Schematic ...................................................................................9
MULTIflow OV: Connection Heights ..................................................................10
MULTIflow SB: Schematic..................................................................................11
MULTIflow SB: Schematic & Connection Heights..............................................12
Technical Data ...................................................................................................13
Installation Schematic (Open Vented)...............................................................14
Installation Schematic (Sealed System).............................................................15
Commissioning ..................................................................................................16
Troubleshooting.................................................................................................18
Warranty............................................................................................................19
Ancillary Descriptions ........................................................................................21
Commissioning Checklist ...................................................................................22
Notes..................................................................................................................25

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Preface
An early adopter of the principal of domestic thermal stores, McDonald Water Storage
first started manufacturing thermal stores in early 1990s. Manufactured by our trained
coppersmiths and designed based upon the experiences of our technical team. The
McDonald Water Storage MULTIflow provides the perfect solution for mains pressure
hot water.
The MULTIflow Thermal Store Installation & Technical Manual should be read in
conjunction with the installation and servicing manuals issued by the manufacturer(s)
of the heat source(s) used within the thermal storage system.
This information provided is intended to provide support with the installation of the
MULTIflow thermal storage system. Responsibility for selection and specification of our
equipment remains that of our customer and any experts or consultants concerned with
the installation(s). Our full Terms & Conditions of Sale are available on request.
The MULTIflow thermal storage system is required to be fitted by a competent installer,
in accordance with Building Regulations G, Gas Safety Regulations, and the Water
Fitting Regulations (England and Wales),Water Fitting Regulations (Northern Ireland)
or Water Byelaws (Scotland).
(Please note the MULTIflow overcomes Safety implications within Building Regulations G3
relating to pressure and temperature discharge requirements, the installation of the MULTIflow
may be notifiable to the relevant building control.)

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Handling & Storage
It is important the MULTIflow is handled with care and stored the correct way up in a
dry place at all times prior to, during and after installation.
Carrying handles are provided in the back of the casing to assist with lifting and
positioning. DO NOT LIFT BY THE PIPEWORK as this can loosen off the pre-tested
pipework and may result in leaks. It is good practice to check the joints before filling
with water in case anything has been loosened in transit. Any manual lifting will need
to comply with the requirements of the Manual Handling Operations Regulations issued
by the Health & Safety Executive. For installations on higher levels of properties such
as the 4th floor it is recommended as best practice for the MULTIflow to be moved
vertically within a lift.
What is a Thermal Store?
•Initially the Thermal Store is filled through either the integral, or a remote,
Primary Feed & Expansion Tank.
•The primary store of water is designed to be heated by Immersion Heaters, Gas
/ Oil Boiler or Central Plant Systems.
•Mains pressure water is fed and heated via a secondary heat exchanger, which
draws its heat from the primary store of water.

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Design
The copper MULTIflow Thermal Store is a primary store that is very well insulated to
ensure minimum Heat Loss and optimally designed to meet the stringent requirements
of ERP.
Cold water at mains pressure passes through a High Efficiency Coil, which is specifically
designed to draw heat from the thermal store at mains pressure. This heated water is
subsequently blended with cold mains water through a Thermostatically Controlled
Mixing Valve, to provide mains pressure water at circa 55°C to the taps and showers.
The Secondary Pipework Loop (DHW Coil & External Pipework) can contain a total of
3 - 5 Litres of water and incorporates an expansion bottle to accommodate the thermal
expansion of the heated mains water. If the volume of the secondary pipework loop
exceeds 15 Litres, then the installer must fit suitable relief valves and appropriately
sized expansion vessels.
The main benefit of the Open Vented Thermal Store configuration is that there is no
onerous discharge restrictions, as required with Unvented Storage Cylinders under G3
regulations.
Where applicable, it also allows the Boilers to input all their power into the store and
reduces boiler cycling.
Being a thermal store that is vented, it is inherently safe and requires no annual
maintenance. Its benefits go one step further as being a primary store there is no
legionella risk, having a blending valve ensures in-built scald protection and then
primary store is not subject to scale build up.

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Mains Water Supply
The MULTIflow’s performance is largely related to the cold water supply pressure and
flow rate incoming to the property.
•The mains supply to the unit should ideally be in a minimum of 22mm diameter
but will work with 15mm if there is adequate pressure and flow rate.
•The MULTIflow will operate with a minimum incoming mains pressure of 1.0 Bar
and a minimum flow rate of 20 Litres/minute.Careful consideration should be
made to ensure the pressure of hot and cold supplies are balanced.
•An incoming pressure of 2.1 Bar is the most optimal for performance.
•If the incoming pressure exceeds 3 Bar, then a pressure reducing valve must be
fitted after the stopcock of where the incoming cold supply enters the property.
•No Pressure Reducing Valve or Check Valve should be fitted within 2 metres of
the Cold Inlet to the MULTIflow Coil.
•If the flow rate exceeds 15 Litres per minute at any tap, it should be restricted
to maintain the performance of the system as a whole.
Immersion Heaters
•Immersion Heaters are preset to ensure the store temperature reaches 70°C
(maximum 75°C) once the unit is heated.
•The Immersion Heater thermostats are preset with the control setting at 70°C
and the high limit setting at 90°C. The control setting can be lowered or
increased as required for the installation requirements.
•If in any doubt of how to set the Immersion or what temperature we would
advise for specific installations, please contact us on 01592 611123.
•All Immersion Heaters should be wired by a qualified electrician as shown
below, for further information refer to literature provided with the immersion;

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Water Treatment
In accordance with the Building Regulations L1A: New Dwellings/ L1B: Existing
Dwellings, the requirements set out in the Domestic Building Services Compliance
Guide specify that “where the mains water hardness exceeds 200ppm provision should
be made to treat the feed water to water heaters and the hot water circuit of
combination boilers to reduce the rate of accumulation of lime scale”. In most instances
of this water condition, an inline Water Conditioner/Scale Inhibitor would be fitted to
the incoming mains.
The water quality shall be in accordance with European Council Directive 98/83/EC, or
revised version at the date of installation, and is not fed with water from a private
supply. Particular:
•Chloride content: Max. 200 mg/l
•Sulphate content: Max. 200 mg/l
•Combination chloride/sulphate: Max. 300 mg/l (in total)
The MULTIflow is part of the primary system the Boiler models (where applicable) and
other parts of the primary circuit will require the application of a protective scale and
corrosion inhibitor such as Fernox to ensure adequate protection. This should avoid
having corrosive material in the primary system and remove any build-up of sludge
which can reduce the performance of the High Efficiency Heat Exchanger Coil.
The volumes and concentration of inhibitor required should be calculated in accordance
with the manufacturer’s instructions. Please ensure that the thermal store volume is
also included as well as the radiator and pipework volume.
While we strongly recommend it, inhibitor is optional where the units are utilised with
electricity only. However if there are doubts regarding the quality of water being used
to fill the MULTIflow, an inhibitor should be added to the appliance when filling in line
with the manufacturer’s instructions for these products.
Please note that in all MULTIflow models, the primary water within the thermal store
water is used as primary storage and the domestic hot water is heated instantaneously
by means of the High Efficiency Heat Exchanger Coil. Therefore, treating the primary
water will not have an effect on the domestic hot water supply.

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Pipework
It is imperative to achieve balanced supply of hot and cold water in a mains pressure
system, and that the piping in a dwelling should be sized in accordance with BS 6700.
However, the following rule of thumb guidelines should be adequate for most of the
smaller property types as long as water pressures are within the recommended range.
•The cold feed from the main incoming stop tap to the MULTIflow should be run
in 22mm pipe. The cold main and hot draw-off should also be run in 22mm as far
as the branch to the bath tap. 
•A 15mm copper or equivalent external service may be sufficient for a small 1
bathroom dwelling (depending upon the flow rate available), but the minimum
recommended size for new dwellings is 22mm (25mm MDPE).
•The internal branches to the hand basins and sinks should be in 10mm and to the
baths and showers in 15mm. (1 metre minimum) 
•A pressure reducing valve must be fitted after the stopcock of where the
incoming cold supply enters the property and at least 2 metres away from the
inlet to the Secondary Water Coil.
Discharge/Overflow Requirements
The MULTIflow is a Vented Thermal Store and therefore does not require safety
discharge from a Pressure and Temperature Relief Valve as highlighted in Part G of the
Building Regulations.
The MULTIflow Thermal Store can be sited anywhere within the property as no
discharge pipework is required. A manual fill Feed and Expansion tank is provided as
standard and we would recommend wherever possible, to ensure an overflow pipe is
connected to a suitable discharge point.
On the OV model, if an open vented central heating system is to be run, ensure a
minimum 500mm from the highest point of the radiator circuit and the bottom of the
Feed & Expansion Tank. Once the unit is filled through the pipework, close off the
isolation valve and disconnect the flexible hose from the pipework and cap the pipe to
avoid any dead legs.

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An Automatic Fill version is available as an optional extra at the time of order. The
overflow must be run to a suitable drain point. A tundish is supplied with the automatic
fill kit, if the overflow termination is difficult to see. The tundish must be fitted vertically,
with continuous fall of the overflow pipe.
The overflow should be run in either 22mm copper tube or high temperature overflow
pipe with suitable supports. Ensure that the overflow is capable of coping with a ball-
valve fail situation and restrict flow to the ball-valve accordingly.
Showers
•MULTIflow cylinders are compatible with all showers.
•Most commonly used are of the Thermostatic Mixing type. All mains pressure
systems are subject to dynamic changes particularly when other hot and cold
taps/showers are opened and closed. This will cause changes in the inlet hot
water temperature and pressure at mixed water outlets such as showers.
•Careful consideration should be taken in selecting specification of the shower
valve to ensure the correct mixed water temperature and pressure is
maintained and that it is suitable for the type of people using it.
•Some showers in the TMV2 range have about a 10 degree differential between
the hot inlet temperature and the mixed outlet temperature, allowing
showering temperatures of up to 48 degrees.
•Other valves such as TMV3 only allow maximum temperatures of 41 degrees.
•Commissioning should ensure that the hot draw off from the thermal store is
set taking this into account.
•Please ensure that the shower head is capable of taking mains pressure.
•Please ensure that the shower tray drain is capable of handling the shower
head flow rate. A flow restrictor may be required in the shower outlet hose.
•The hot water supply to a shower-mixing valve should be fed wherever
practical directly from the MULTIflow or be the first draw-off point on the hot
circuit.
•The cold supply to a shower-mixing valve should wherever practical be fed
directly from the incoming mains. To ensure balanced pressure for the shower
mixing valve, a pressure reducing valve must be fitted after the stopcock of
where the incoming cold supply enters the property.
•The shower must incorporate or be fitted with the necessary check valves to
provide back-syphonage protection in accordance with the Water Regulations.

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MULTI flow OV: Schematic
Standard manual fill model shown above.
3kW
3kW
Expansion Pipe
Feed Pipe
Hot Out
c/w Thermostatic
Mixing Valve
Expansion
Bottle
Cold Mains
Secondary Water
High Efficiency
Secondary Coil
Boiler Flow
Boiler Return
Immersion Heater
(On Peak)
Boiler Control Stat
@ 70⁰C
Drain
Immersion Heater
(Off Peak)
Sight Glass

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MULTI flow OV: Connection Heights
The connection heights shown below are taken from the ground (in mm).
Capacity (Litres)
120
150
180
210
Height
1000
1200
1400
1600
Width
560
560
560
560
Depth
605
605
605
605
Drain
120
120
120
120
Off Peak IH
170
170
170
170
On Peak IH
550
650
750
850
Boiler Flow
790
980
1130
1390
Boiler Return
230
230
230
230
Control Stat
400
400
400
400
Hot Out (Coil)
855
1035
1190
1340
Cold In (Coil)
275
275
390
590
Allow an additional 100mm to the width where pipework is connected through the side
of the unit.

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MULTI flow SB: Schematic
Standard manual fill model shown above.
3kW
Expansion Pipe
Feed Pipe
Hot Out
c/w Thermostatic
Mixing Valve
Expansion
Bottle
Cold Mains
Secondary Water
High Efficiency
Secondary Coil
Boiler Coil Flow
Boiler Coil Return
Boiler Control Stat
@ 70⁰C
Drain
Immersion Heater
(Off Peak)
Sight Glass

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MULTI flow SB: Schematic & Connection Heights
The connection heights shown below are taken from the ground (in mm).
Capacity (Litres)
120
150
180
210
Height
1000
1200
1400
1600
Width
560
560
560
560
Depth
605
605
605
605
Drain
120
120
120
120
Off Peak IH
170
170
170
170
Boiler Flow
470
500
600
700
Boiler Return
230
230
230
230
Control Stat
400
400
400
400
Hot Out (Coil)
855
1035
1190
1340
Cold In (Coil)
275
275
390
590
Allow an additional 100mm to the width where pipework is connected through the side
of the unit.

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Technical Data
ERP / Heat Loss Data
Capacity (Litres)
120
150
180
210
Insulation Thickness (mm)
50
50
50
50
ERP Class
C
C
C
C
Standing Heat Loss (Watts)
49
57
65
69
Standing Heat Loss (kWh/day)
1.18
1.37
1.56
1.66
Thermal Stores have been tested in accordance with HWA Thermal Store Specification
(Multifuel). Heat losses should not be directly compared with heat losses from unvented/vented
cylinders because the unvented/vented cylinders are tested at 65°C and the thermal store at
75°C so they are treated differently in SAP.
Selection Chart
Sizing Guide
120
150
180
210
Bedrooms
1
1-2
2-3
2-3
Baths & Showers
1
1
2
3

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Installation Schematic (Open Vented)

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Installation Schematic (Sealed System Boiler)

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Commissioning
The below is a recommended guide of actions and checks that should be undertaken
during commissioning:-
DO
✓During commissioning, complete all relevant sections of the Commissioning
Checklist (Page 21-23). This must be completed during commissioning and left
with product to meet the Warranty conditions.
✓Check the incoming mains water pressure. If the incoming mains pressure is higher
than 3.0 Bar, fit a Pressure Reducing Valve set at 3.0 Bar maximum –recommended
2.1 Bar where the cold supply enters the property as this will create balanced
pressure throughout.
✓Ensure that connections are fitted in accordance with the sketch supplied
✓Ensure the drain is connected to allow draining of the unit if required. If a drain-
cock is fitted, we recommend a DZR fitting.
✓Fit the Overflow with Copper piping or high temperature plastic to the thermal
store system where required.
✓Ensure minimum of 225mm between the top of the tank and ceiling to allow access
to service the ball-valve if ever required.
✓Check that all pipework connections on the MULTIflow are tight with pipes fully
inserted following transit and handling.
✓Fill the MULTIflow via the Feed & Expansion Tank.
✓Ensure the system is inhibited correctly –see page 6.
✓Check the water level in the Feed & Expansion Tank.
✓On the Manual Fill version, once the unit is filled through the pipework, close off
the isolation valve, disconnect the flexible hose from the pipework and cap the pipe
to avoid any dead legs.
✓Check for leaks throughout the thermal storage system.
✓Run all taps and other hot outlets to remove all air from the system.
✓Electric only - Immersion Heaters should be set at 70⁰C to meet users’ hot water
requirements.

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✓Boilers –Set the boiler pump to its highest setting. Set the Boiler Thermostat and
also the MULTIflow thermostat to maximum. Fire the boiler on HOT WATER ONLY
setting and wait until the boiler goes off. Turn the cylinder thermostat down slowly
till it clicks off, then turn it down by approximately 2⁰C. This should mean that the
MULTIflow thermostat controls the system. This can be checked by running off
some of the hot water, re-firing the boiler and checking that the MULTIflow
thermostat is in control.
✓Ensure the store temperature is set to 70⁰C (70⁰C minimum and 75⁰C maximum)
on the store temperature gauge. This can be increased but consideration should be
made for the temperature and pressure rise, caused by “creeping”, where small
draw offs are present.
✓Temperature Controls must be fitted to ensure safe temperature of Thermal Store
✓On installs where central heating is run from the MULTIflow, ensure that 500mm
height difference is in place between the highest point of the radiator circuit and
the bottom of the Feed & Expansion Tank.
✓Ensure that all exposed pipework on the MULTIflow is insulated to minimise any
heat losses.
✓Ensure the Thermostatic Mixing Valve is adjusted to control the hot water outlet
temperature between 50 - 55°C (take shower differential into consideration).
✓Check the boiler pump setting is set as high as possible without emitting excessive
noise to prevent a boiler temperature differential of greater than 11°C.
✓If required, chlorinate the hot and cold water system in accordance with BS 6700
and Water Regulations. Please note that the whole of the domestic hot and cold
water systems must be adequately flushed after chlorination. Failure to do so will
cause damage to the exchangers/immersion heaters etc.
DON’T
Use a combined feed and vent.
Use tube smaller than 28mm between boiler and MULTIflow if the boiler exceeds
an output of 60,000 Btu (17kW).
Place any clothing or other combustible materials against or on the MULTIflow.

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Troubleshooting
Below contains a troubleshooting and solution guide to the thermal store system. If
this table does not resolve your problem, please contact either your installer or phone
McDonald Water Storage Technical Team for further advice.
SYMPTOM
SOLUTION
The water at the tap
is lukewarm or cold.
The thermal store is designed to work best when the store
temperature is at or approaching 70°C - 75°C. While the thermal
store can provide hot water at lower temperature storage, the
available flow rates and volume will be reduced. Check the
thermometer is showing the store temperature is at or approaching
70°C- 75C. If this is not the case;
1) Where a boiler has been incorporated, ensure that the boiler is
firing, that the control thermostat is set at 70⁰C and allow
sufficient time for the store to reach working temperature.
2) On the Electric model, a qualified electrician should check that
the immersion heater is working, the control thermostat is set at
70⁰C, the safety cut-out has not tripped, and receiving the
correct supply at the correct time (off-peak).
The thermal store is
at 70°C and the
water at the taps is
still lukewarm or cold
1) If the store is at or approaching 70°C - 75C, check that the
Thermostatic Mixing Valve is correctly set. The maximum
temperature of water from the Mixing Valve should be about
55C.
2) If the valve is correctly set, check that the flow rate at any outlet
(e.g. bath tap) does not exceed 15 Litres per minute. If the flow
rate is too high then sufficient heat transfer inside the
MULTIflow may not be occurring.
Turn the flow through the tap down or fit a suitable flow
restrictor and the temperature will increase.
3) If Stage 1 and 2 has not resolved the problem a competent
installer should check the mixing valve for blockages within the
internal filter of the mixing valve.
Not enough hot
water and store less
than 70°C.
Check the heat sources and their input in (kW) to the store as this will
be lower than the kW output which will result in the store not
producing enough heat for the exchanger to provide heated mains
pressure water.

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There is a brownish
tint to the mains
pressure hot water.
This could be a symptom with the heat exchanger coil leaking inside
the thermal store. An installer should have this tested. If this is the
case, pay attention to the Feed & Expansion Tank as the pressure
within the store will increase causing the tank to overflow continually.
MULTIflow is set at
70°C but the mains
pressure
temperature drops
quickly when running
a tap (e.g. bath)
1) If an inhibitor has been installed, check with the installer that it
has been installed at the correct proportion and checked at
appropriate frequencies.
2) The in-line strainer in the cold mains supply to the unit may be
choked and require cleaning.
3) Carefully check the hot water temperature flow into the mixing
valve. If it is very hot, it may be that the valve needs to be
checked / replaced. A competent installer should check the
mixing valve for blockages within the internal filter.
4) If the DHW Coil is giving an initial heat transfer and then fading,
this could be a sign of scale build up inside the Heat Exchanger
Coil, especially if in a known hard water area. A competent
installer would need to descale the DHW coil and check/fit
descaling equipment.
Warranty
McDonald Water Storage guarantee the MULTIflow shell against material defect or
manufacturing fault for a period of 5 years from the date of delivery. Components
are guaranteed for 2 years.
The above product guarantee is valid provided:
•It has been installed by a competent installer in accordance with the
instructions detailed in our installation manual and all relevant Codes of
Practice and Regulations in force at the time of installation.
•No factory fitted parts have been removed for unauthorised repair or
replacement and the product has not been modified –other than by
McDonald Water Storage.
•Any replacement parts should be purchased from McDonald Water Storage.
•The hot water store has only been used for the storage of potable water
supplied from the public mains (Max –200mg/litre chloride). And treated as
detailed in the installation instructions.