McDonald Engineers UK THERMflow User manual

Technical Manual
THERMflow
Boiler Model
McDonald Engineers UK
November 2017
THERM flow Boiler Model Technical Manual
HOT WATER SOLUTIONS SINCE 1945

1
Contents
Design ..................................................................................................................2
Preface.................................................................................................................2
Handling & Storage..............................................................................................2
What is a thermal store? .....................................................................................3
Basics of the Thermal Store.................................................................................3
Mains Water Supply ............................................................................................4
Water Treatment.................................................................................................4
THERMflow Combination General Schematic .....................................................5
THERMflow Cylinder General Schematic.............................................................6
THERMflow Connection Heights..........................................................................7
THERMflow with External PHE ............................................................................8
THERMflow Combination with PHE General Schematic......................................9
THERMflow Cylinder with PHE General Schematic ...........................................10
Commissioning...................................................................................................11
Commissioning Best Practice.............................................................................12
Troubleshooting.................................................................................................13
Schematics.........................................................................................................15
Ancillary Descriptions ........................................................................................18
Installing a Gravity System.................................................................................20

2
Design
An early adopter of the principal of domestic thermal stores, McDonald Engineers UK
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 Engineers UK THERMflow provides the perfect solution to both mains
pressure hot water and space heating requirements.
Preface
The THERMflow 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, such as the boiler/solid fuel boiler, solar etc.
This information provided is intended to provide support with the installation of the
THERMflow 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 THERMflow thermal storage system is required to be fitted by a competent installer,
as defined by the relevant regulations e.g. Gas Safety Regulations. Please note that
while the THERMflow overcomes Part G Building Regulation discharge requirements
for unvented cylinders, the installation of the THERMflow may be notifiable to the
relevant building control.
Handling & Storage
It is important the THERMflow is handled with care and stored the correct way up in a
dry place at all times prior to, during and after installation. 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 THERMflow to be moved
vertically within a lift.

3
What is a thermal store?
Often used in conjunction with a variety of alternative energy sources such as solid fuel,
wood burning stoves and solar, a thermal store captures input energy from heat sources
to allow that energy to be converted into mains pressure hot water and space heating
at a later time when the demand is greater. Energy from a heat source is captured within
the primary water of an open vented cylinder at a temperature of up to 80°C.
Cold water at mains pressure then passes through a High Efficiency Coil, which is
specifically designed as a heat exchanger, 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 55°C to
the taps. In addition, the primary water captured within the store can also be circulated
around the heating system allowing the householder to enjoy the benefits of mains
pressure water and heating produced from alternative and renewable heat sources.
Basics of the Thermal Store
The THERMflow Boiler Model utilises open vented boilers and/or Electric Immersion
Heaters as its primary heat source/s, with options available for wood burning, AGA, solid
fuel boiler and underfloor connections amongst others.
The main benefit of the Open Vented Thermal Store configuration is the open vented
nature allows the full power (kW) output of the boiler directly into the thermal store, as
no heat exchanger is required thus reducing energy usage and running costs. Input
energy from the boiler(s) is circulated from the thermal store to the central heating
system while the High Efficiency Secondary Coil is specifically designed to provide high
performance blended mains pressure hot water to the taps at 55°C.

4
Mains Water Supply
The THERMflow’s performance is directly related to the cold water supply pressure and
volume incoming to the property. The THERMflow will operate with a minimum
incoming mains pressure of 1.0 Bar. A maximum incoming pressure of 3.0 Bar would be
the most optimal for performance. If the incoming mains pressure is higher than 3.0
Bar, a pressure reducing valve must be fitted downstream of where the incoming cold
supply enters the property at a lesser and appropriate pressure.
If the flow rate exceeds 20 Litres per minute at any tap, it should be restricted to
maintain the performance of the system as a whole.
Water Treatment
The THERMflow is part of the primary system and while it does not require any special
water treatment itself, the radiators 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.
Please note that in all THERMflow 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.

5
THERM flow Combination General Schematic
Immersion Heater
22mm Boiler Flow
(Other Sizes Available)
28mm Solid Fuel Return
(Other Sizes Available)
3kW
⁰C
Thermometer
22mm Central
Heating Flow &
Return Connections
(Other Sizes Available)
15mm Drain
Cold Mains
Secondary Water c/w
Check Valve & Strainer
Hot Out
c/w Thermostatic
Mixing Valve
2 Litre
Expansion
Bottle
High Efficiency
Secondary Coil
Maintenance Free
Jetseal Ballvalve
High-Limit
Stat
@ 90⁰C
Control Stat
@ 75⁰C
Overflow
(Not fitted as standard)
22mm Boiler Return
(Other Sizes Available)
28mm Solid Fuel Flow
(Other Sizes Available)

6
THERM flow Cylinder General Schematic
22mm Boiler Flow
(Other Sizes Available)
28mm Solid Fuel Return
(Other Sizes Available)
3kW
⁰C
Thermometer
22mm Vent
22mm Central Heating
Flow & Return
Connections
(Other Sizes Available)
15mm Drain
Immersion Heater
Cold Mains Secondary Water
c/w Check Valve & Strainer
Hot Out
c/w Thermostatic
Mixing Valve
22mm Cold Feed
2 Litre
Expansion
Bottle
Secondary Return
(Optional)
High Efficiency
Secondary Coil
High-Limit Stat
@ 90⁰C
Control Stat
@ 75⁰C
28mm Solid Fuel Flow
(Other Sizes Available)
22mm Boiler Return
(Other Sizes Available)

7
THERMflow Connection Heights
The connection heights shown below are taken from the ground (in mm). These
heights and the diagrams shown above are indicative of a typical arrangement of
connections, including optional extras. Bespoke options for specific installation are
available and will be supplied with a sketch prior to manufacturing of the THERMflow.
Capacity (Litres)
120
140
180
210
250
300
Shell Dimensions
900 x
450
1050 x
450
1300 x
450
1500 x
450
1500 x
500
1800 x
500
Overall Dimensions
950 x
550
1100 x
550
1350 x
550
1550 x
550
1550 x
600
1850 x
600
Cold Feed (Cyl. Only)
100
100
100
100
100
100
Drain
100
100
100
100
100
100
(3kW) IH
155
155
155
155
155
155
CH Flow
170
320
470
670
670
970
CH Return
100
100
100
100
100
100
Boiler Flow
700
850
1100
1300
1300
1600
Boiler Return
100
100
100
100
100
100
SF Flow
550
700
950
1150
1150
1450
SF Return
100
100
100
100
100
100
Thermostat
350
350
350
350
350
350
Thermometer
500
500
500
500
500
500
Hot Out
700
850
1100
1300
1300
1600
Cold In
220
370
520
720
720
1020

8
THERM flow with External PHE
An External Plate Heat Exchanger (PHE) can be fitted to a THERMflow in replacement
of the internal High Efficiency Coil. A THERMflow with an External PHE is an alternative
to the standard thermal store, for properties with varying hot water demands. Instead
of an internal High Efficiency Coil, a Plate Heat Exchanger is fitted to the external
pipework of the cylinder. In areas with high corrosion or limescale, it is easier to
replace the PHE as required.
The cold mains is fed through the Secondary flow of the PHE, whilst the primary water
storage is pumped through the Primary flow of the PHE, allowing for instantaneously
heated water. The Primary water storage flow is controlled by a Charging Pump, whilst
the Secondary flow is controlled by a Flow Switch Valve. Both the Pump and Switch
are controlled through a Wiring Centre, installed on the side of the cylinder.
It utilises similar heat sources (e.g. solid fuel, central heating etc.) for the primary
water storage, and has a similar set up of connections to the standard thermal store
combination/cylinder. However with Combination Units, a Ballvalve is not required
within the Header Tank if the cylinder is a Manual Fill, and is instead replaced with an
Overflow connection, as shown in the following diagram.

9
THERM flow Combination with PHE General Schematic
22mm Boiler Flow
(Other Sizes Available)
28mm Solid Fuel Flow
(Other Sizes Available)
External Plate
Heat Exchanger
3kW
⁰C
Thermometer
Overflow
(Not fitted as standard)
22mm Central
Heating Flow &
Return Connections
(Other Sizes Available)
15mm Drain
Immersion Heater
Cold Mains
Secondary Water
c/w Flow Switch
Charging Pump
Hot Out
c/w Thermostatic
Mixing Valve
Wiring Centre
28mm Solid Fuel Return
(Other Sizes Available)
22mm Boiler Return
(Other Sizes Available)
High-Limit Stat
@ 90⁰C
Control Stat
@ 75⁰C
Maintenance Free
Jetseal Ballvalve

10
THERM flow Cylinder with PHE General Schematic
22mm Central
Heating Flow &
Return Connections
(Other Sizes Available)
15mm Drain
Cold Mains
Secondary Water
c/w Flow Switch
Charging Pump
Wiring Centre
22mm Cold Feed
22mm Boiler Flow
(Other Sizes Available)
28mm Solid Fuel Flow
(Other Sizes Available)
External Plate
Heat Exchanger
22mm Vent
Hot Out
c/w Thermostatic
Mixing Valve
22mm Boiler Return
(Other Sizes Available)
28mm Solid Fuel Return
(Other Sizes Available)
3kW
⁰C
Thermometer
Immersion Heater
High-Limit Stat
@90⁰C
Control Stat
@75⁰C

11
Commissioning
When commissioning the Boiler Model the following steps should be undertaken:
1. Connect the relevant central heating and boiler(s) flow and return pipework in
accordance with the corresponding connections on the store (as indicated on the
sketch provided).
2. Connect the mains to the Cold In and turn the mains on. Fit Pressure Reducing Valve
@ 3.0 Bar if required.
3. Check for leaks throughout the thermal storage system.
4. All normal procedures for a Vented Primary System apply. Drain the system, hot
flush and re-fill. Add Inhibitor as required (see Water Treatment section on Page
5), re-bleed the radiators and any high points of pipework.
5. Once complete, set the Boiler Pump to its highest speed setting (usually setting 3).
Set the boiler thermostat and also the Boiler Control Thermostat on the thermal
store to maximum.
6. Fire the boiler on the “Hot Water Only”setting and wait until the boiler goes off.
Turn the Boiler Control Thermostat down slowly till it clicks off, then turn it to 75°C.
(This should mean that the cylinder thermostat on the THERMflow controls the
system. This can be checked by running off some hot water which should lead
to the boiler re-firing)
7. Set the Solid Fuel Thermostat to ensure that the Central Heating Pump will pump
in an overheat situation or if the Room Stat requests for the heating to be turned
on (Normally 85 - 90⁰C).
8. Check that the hot water at the taps is at a suitable temperature for the
householder. The temperature can be increased or decreased by adjusting the
factory fitted Thermostatic Mixing Valve (which will be pre-set).
9. Once complete adjust the boiler and Central Heating Pumps to provide maximum
flow rate without emitting excessive noise.
10. Finally run all taps and other hot outlets to remove all air from the system.

12
Commissioning Best Practice
The below is a recommended guide of actions and checks that should be undertaken
during commissioning:-
DO
Fit an Overflow with Copper piping to the thermal store system.
Check the incoming mains water pressure, if it exceeds 3.0 bar, fit a Pressure
Reducing valve set at 3.0 bar and 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.
Fill the Feed & Expansion Tank manually and adjust ball valve so water is at lowest
level.
Ensure sufficient clearance above the Feed & Expansion Tank to allow for access.
Ensure sufficient clearance for External Plate Heat Exchanger & Pipework.
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 is insulated to minimalise any heat losses.
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.
Leave on the power after the thermal store has been filled to prevent the central
heating and boiler pump from sticking.
DON’T
Use a combined feed and vent.
Use tube smaller than 28mm between boiler and THERMflow if the boiler exceeds
an output of 60,000 Btu (17kW) output.
Place any clothing or other combustible materials against or on the THERMflow.

13
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 Engineers UK 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 75°C - 80°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
75°C- 80C. If this is not the case, ensure that the boiler is firing and
allow sufficient time for the store to reach working temperature.
The thermal store is
at 80°C and the
water at the taps is
still lukewarm or cold
1) If the store is at or approaching 75°C - 80C, check that the
Thermostatic Mixing Valve is turned to hot. The maximum
temperature of water from the Mixing Valve is 55C.
2) If the valve is turned fully to hot, check that the flow rate at any
outlet (e.g. bath tap) does not exceed 20 Litres per minute. If
the flow rate is above this, then turn the tap down slightly.
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 less than
80°C on the
thermometer.
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.
THERMflow is set at
80°C but the mains
pressure
temperature drops
quickly when running
a tap (e.g. bath)
1) Check with the installer that inhibitor has been put in frequently.
If the DHW Coil is giving an initial heat transfer and then fading
this could be a sign of sludge build up surrounding the Heat
Exchanger Coil, which will reduce the performance of the store.
2) If Stage 1 does not resolve the problem, the balance of inputs
and outputs may be affecting performance. This can be tested
by drawing off the same flowrate of water when the output is
lower, such as turning your heating off.
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.

14
Copper Feed & Expansion Tanks
The Feed & Expansion Tank (provided by the installer) must be sized correctly to
enable the expansion of the entire system volume, made up of the thermal store,
radiator and boiler circuit volumes. We recommend that the Feed & Expansion Tank
should be sized to approximately 15% capacity of the total system to cope with the
thermal expansion.
*Sizes indicated are from McDonald Engineers UK Feed & Expansion Tank Sizes
Given the high temperatures of up to
100°C that can be discharged from the
thermal store through inputs from
heat sources such as solid fuel, it is
recommended that the feed and
expansion tank is designed to
withstand temperatures over 100°C.
McDonald Engineers UK manufacture a Premium Grade Copper Feed & Expansion Tank
designed to withstand these temperatures, available as an optional extra, please
contact McDonald Engineers UK on 01592 611123 for more information.
Feed & Expansion Tank Capacity Calculator
Cylinder Capacity
(Litres)
120
140
180
210
250
300
Estimated
Primary Capacity
(Litres)
138
161
207
241.5
287.5
345
Recommended
F&E Capacity
(Litres)
20
20
30
30
40
50
Overall Height
and Diameter of F
& E Tank (mm)
400 x 420
400 x 420
375 x 470
375 x 470
470 x 470
500 x 520
½” c/w Jetseal
Maintenance Free Ball
Valve & Copper Float
100mm
1”Feed
1”Overflow
1”Expansion

15
Schematics

16
Pump Kit Wiring Diagram

17
THERM flow with External PHE, Wiring Diagram
Flow Switch
Wiring Centre
Charging Pump
L
N
Mains
L
N
E

18
Ancillary Descriptions
The following spare parts are available to purchase from the Website, with additional
information provided.
Follow the link below:
https://www.mcdonald-engineers.com/spares
Expansion Vessels (WU2EV)
2 Litre Nitrogen Expansion Vessels are connected to the High
Efficiency Secondary Water Coil Heat Exchanger Pipework to absorb
the increase in pressure caused by thermal expansion within the
Coil. When the thermal expansion occurs the internal diaphragm
expands and contracts based upon the pressure set by the
Expansion Vessel. For best performance it is recommend setting the
Expansion Vessel to match the incoming pressure.
Low Watts Density Immersion Heaters (WIHLWD)
The THERMflow are fitted with a 3kW 16” Incoloy Immersion Heater
complete with Combined Control Thermostat and Resettable Safety
Cut-Out. The LWD Immersion Heater is designed with reduced noise
emission and a longer lifespan when used with higher temperatures
and are suitable for more aggressive water conditions.
Cylinder Thermostat (WTCT)
Cylinder Thermostats allow for highly responsive temperature control to
your central heating, and boiler(s) by switching on and off the heat
supply from the boiler(s) and to the heating. The THERMflow’s Boiler
Control Stat will be used to bring the thermal store up to a maximum of
75°C- 80°C and control the boiler. The Solid Fuel Stat will be linked to the
Central Heating Pump and will pump part of the contents of the
THERMflow to a heat leak radiator in order to cool down the thermal
store in the event of an overheat situation from an uncontrollable heat
source such as solid fuel.
Thermostatic Mixing Valve (WTTMV / WTTMVS)
The Thermostatic Mixing Valve blends the hot water leaving
the High Efficiency Secondary Coil which can often be over 60°C
with cold water to ensure constant, safe outlet temperatures
at 55°C to prevent scalding.
WTTMV
WTTMVS

19
Thermometer (WTHERM)
The 2” Side Entry Thermometer allows for a temperature reading of the
thermal store to be taken from the side of thermal store to ensure the
thermal store is operating at the correct temperature.
Thermal Store Pump (WTP)
Designed with a three-speed motor to circulate round domestic heating
systems, the thermal store pump are designed to pump to the central
heating and boilers of domestic central heating systems of up to 35kW.
THERMflow Programmer (WTPROG)
The THERMflow programmer allows you to set “On” and “Off” time
periods to switch the central heating on and off to suit the user’s
requirements.
THERMflow Wiring Centre (WTWC)
Acting as the relay for the wiring cables from the programmer, boiler,
pumps and stats to ensure the thermal store operates correctly.
Pressure Reducing Valve (WUVPRC)
Designed to regulate the incoming mains pressure to a fixed pressure.
Plate Heat Exchanger (WTPHE)
Exchanges hot water temperature from cylinder with
secondary flow. Insulation is included. Flow rates must
be specified when ordering. (Only for THERMflow
models with External PHE).