Installation Instructions for the Mech HIU

From Heatweb Wiki
Jump to: navigation, search


Thermal Integration MECH

Assembly instructions & user manual.

Please retain this document with the HIU.

APPLICATION: The Thermal Integration MECH HIU is designed for use as a Heat Interface Unit (HIU) connected to a communal heat distribution system and is suitable for provision of both heating and hot water. It can be fitted with an MID approved Class 2 heat meter to enable energy monitoring. In order for the MECH HIU to serve the heating circuit and achieve virtually instantaneous hot water delivery, the communal heat distribution system should be up to temperature and pumped at all times. A pressure operated bypass should be fitted to the system to allow a small amount of flow when all units are shutdown, as this helps maintain heat in the pipework ready for any demand.

The MECH HIU uses a gas filled mechanical control valve to accurately regulate DHW. Central heating is provided directly, with a Differential Pressure Control Valve fitted on the CH feed. DHW temperature can be adjusted by the resident without removing the HIU casing or breaking any of the security seals.

The unit comes in an attractive EPP casing, with overall dimensions of only 585mm W x 485mm H x 265mm D, and remarkably low heat losses < 20W.

LOCATION: The HIU should be installed with the following provisions:

  • HIU should be installed in a frost-free area
  • HIU should not be exposed to direct sunlight.
  • Ambient temperature: 5C to 40C
  • Humidity range: 10% - 85%


  • The unit must only be installed, commissioned and maintained by a qualified engineer.
  • Installations must take into account all current and relevant Building Regulations, safety requirements for heating installations, and general requirements for drinking water.
  • The unit is solely for an unvented heating system and a maximum temperature of 95ºC.


  • The unit, pipes and radiators can contain water up to 95°C and at high pressure.
  • Contact with components or hot water can cause burns.


  • The Thermal Integration MECH HIU does not contain any electrical controls as it is mechanically controlled. However the heat meter may be mains powered (depending on the model) and may not be waterproof so it should always be kept dry.


  • The differential pressure controller maintains constant differential pressure across your heating system. This pressure differential facilitates heat flow from the distribution network through your heating system. The heating system controls provided in the home, determine the temperature in each room.
  • The MECH HIU is equipped with a plate heat exchanger which uses the heat supplied from the distribution network to provide hot water.


For proper operation of the device a periodic maintenance inspection must be carried out. Maintenance and repairs should be only be done by a qualified engineer.


  • Ensure the unit’s power supply is isolated.
  • Ensure the valves from the district heating supply flow and return are closed
  • Check valves and filter for dirt and contamination.
  • The casing can be cleaned with a damp cloth. Do not use solvents such as benzene, alcohol, etc.

GOING ON HOLIDAY? Do not disconnect the unit from the power supply. The HIU is designed that with no heating or hot water demand, there is virtually no heat and very little electricity used. Turning off the device during prolonged periods of absence is therefore not necessary. Simply set the room thermostat to approximately 12°C before you leave for the duration of your absence.

Contact Thermal Integration for more advice and information on prolonged absence.

Technical Specification

Function Units Value
Hot Water  
Maximum Output  kW 31
Pressure Loss  kPa 18
Capacity  L/min 9
Temperature Range  °C 35 to 60
Maximum Output  kW 42
Differential Pressure Controller Setpoint kPa 20
Kvs Value m³ / Hr 2.5
District Heating Circuit  
Maximum Flow Temperature  °C 95
Pressure Class  Bar PN10
Minimum Flow Temperature  °C 70
Maximum Permissible Pressure  kPa 200
Minimum Differential Pressure  kPa 70
Maximum Pressure Loss  kPa <25
District Heating Flow G ¾" F
District Heating Return G ¾" F
Cold Water Supply G ¾" F
Hot Water G ¾" F
Heating Flow G ¾" F
Heating Return G ¾" F
Heat Meter (Flow Mounted) G ¾” Swivel Nut (x2) L=110mm
Heat Meter Return Temperature Sensor M10 x 1 – into G ½” Adaptor
Height mm 485
Width mm 585
Depth mm 265
Weight incl. Pre-plumbing Bracket kg 9.5
Weight excl. Pre-plumbing Bracket kg 9
(1) The DHW flow capacity depends on the supply temperature, permissible return temperature and
pressure of the distribution network. By means of a flow restrictor in the Mains cold water fitting on
the plumbing bracket, the maximum DHW flow rate can be tuned to these external factors.
(2) The HIU should be mounted on a standard plumbing bracket (Supplied with the Digi Unit).

Overview of Components and Connections

Eco Mech Key.png
  1. Primary flow temperature sensor
  2. Primary circuit strainer
  3. Domestic hot water temperature control
  4. Case security fixing
  5. Plate heat exchanger (DHW Only)
  6. EPP Casing
  7. Heat meter screen (Where fitted)
  8. Domestic hot water temperature sensor
  9. Differential pressure control valve
  10. Heat meter body (Where fitted)
MECH Scope Of Delivery.jpg
MECH Tools.jpg
MECH Dimensions.jpg

Dismantling and Assembly

MECH Dismantle.jpg
MECH Dismantle2.jpg


MECH Commissioning.jpg
MECH Commissioning DPCV.jpg
MECH DHW Valve Setting.jpg

Fitting Insulation Cover

MECH Insulation Cover.jpg

Basic Troubleshooting

1. Close all valves on the plumbing bracket under the unit and the mains cold water feed.
2. Contact your engineer.
Central Heating Circuit does not heat
1. Make sure the valves on the plumbing bracket are open (handle in vertical position).
2. Check radiator valves are open and calling for heat.
3. Check the programmer is set to ON, and calling for heat.
4. Set the room thermostat higher.
5. Problem solved? If not, contact your engineer.
No Domestic Hot Water
1. Check that the mains cold water valve is open. If not, open the main valve.
2. Problem solved? If not, contact your engineer.
Water is not hot
1. Ensure that all valves on the plumbing bracket under the unit and the main valve are open.
2. Make sure the power cord is plugged in and turned on. If in doubt contact an electrician.
3. Problem solved? If not, contact your engineer.
It is normal that the HIU makes noise when hot water or heating are active. If the HIU starts to make any loud or disturbing noises, contact your installer.

Advanced Troubleshooting

Complaint Cause Solution
Note: Close all valves on the plumbing bracket under HIU and the mains water valve.
Weeping from connection Coupling nut is loose / Gasket missing
Tighten union nut / Insert gasket
Weeping from temperature sensor O-ring is missing/ O-ring damaged Replace temperature sensor
Differential pressure control valve  leaks
Connection nipple (s) loose Tighten connection nipple (s)
Differential pressure control  valve damaged
  Replace valve
Other components or pipes leak Component or pipe damage Replace component or pipe
Central Heating System does not heat
Radiators are not warm Valves on plumbing bracket closed Open valves on the plumbing bracket
  Radiator valves closed Open radiator valves
  Air in heating pipe Bleed air from heating system
  Tap is open Close tap
  Filter blocked Clean filter
Pressure and / or temperature of district heating network does not conform with demand
Check pressure and / or temperature of district heating distribution network
Possible defect in temperature sensor or heating valve
Contact Engineer
No Domestic Hot Water
No water No water pressure
Check / open main valve  Check flow limiter for proper placement  and / or blockages
Domestic Hot Water is not at the right temperature
Water is not hot Pre-payment and / or return valves closed
Purchase energy and / or open return valve on heat distribution network
  Low flow rate,1 lt / min is not being achieved
Open the tap to achieve at least 2 lt / min and / or open valves fully
  Flow Sensor defect
Replace flow sensor
Pressure and / or temperature of district heating network does not conform with demand
Check pressure and / or temperature of district heating distribution network
  Filter blocked Clean filter
Possible defect in temperature sensor or heating valve
Contact Engineer
Insulation Cover will not close
Cover does not close properly Cables caught between sheathing
Make sure cables are in slots provided and keep cables free of the insulating jacket
  Pipe spacer is not seated correctly in the slot Press pipe spacer into slot fully
  Heat meter hitting against the inside of case Check correct installation dimensions and adjust position as required
NOTE: It is normal that the HIU makes noise when hot water or heating are active.
Rattling sound Flow sensor incorrectly installed Flow Sensor correct installation (up arrow)
Other Sound   Contact Engineer

General Plumbing Requirements

NEW COMPLETE SYSTEM INSTALLATIONS: When carrying out a completely new heating system installation in a new build property or a first time installation in an existing property, then the heating system must conform to current building regulations Part L1a. All new domestic heating systems must have a minimum of two heating zones. Each of these zones should be controlled by a thermostat and zone valve. Alternatively individual electronically controlled Thermostatic Radiator Valves may be fitted. If domestic hot water is provided by a storage system then the storage system or cylinder will require separate time and temperature control.

All radiators must have TRV's fitted in all rooms except bathrooms and any rooms where a thermostat is located. The exception to this are single storey, open plan dwellings where the living area is more than 70% of the total usable floor area. Then this type of dwelling can be controlled as one zone.

EXISTING INSTALLATIONS: When carrying out boiler replacements on an existing system, the regulations do not require separate zoning of the upstairs and downstairs and compliance with the regulations can be achieved by a single room thermostat or programmable room thermostat. It is however recommended that TRV's are fitted to all rooms except the bathrooms and the room where a thermostat is located.

The appliance must be installed in accordance with, and comply to, the current: IEE Regulations, Building Regulations, Building Standards (Scotland) (Consolidation), Building Regulations (Northern Ireland), local water by-laws, Health & Safety Document 635 (The Electricity at Work Regulations 1989) and any other local requirements.

BRITISH & IRISH STANDARDS Where no specific instruction is given, reference should be made to the relevant British and/or Irish Standard codes of Practice.

  • BS7074:1 Code of practice for domestic and hot water supply
  • EN12828 Central heating for domestic premises
  • BS7593 Treatment of water in domestic hot water central heating systems
  • ECTI National rules for electrical installations

POTABLE WATER: All seals, joints and compounds (including flux and solder) and components used as part of the secondary domestic water system must be approved by WRAS.

FITTING AND MODIFICATIONS: Fitting the appliance and any controls to the appliance may only be carried out by a competent engineer. Any misuse or unauthorised modifications to the appliance or associated components and systems could invalidate the guarantee and may lead to serious injury or even death. The manufacturer accepts no liability arising from any such actions, excluding statutory rights.

SERVICING: The end user should be advised to have the system serviced annually by a competent engineer. Contact Thermal Integration Ltd for a list of approved engineers. Approved spares must be used to help maintain the economy, safety and reliability of the appliance. The service engineer must complete the Service Record after each service.

Guarantees and After Sales Backup for HIUs

Heat Interface Units (HIUs) carry the following guarantees as standard:


1. The warranty begins on the date of delivery. A dated delivery note will be issued to the customer and a copy will be stored by Thermal integration.

2. 12 Months Parts and labour - Parts or labour proven to be defective will be replaced / repaired free of charge for a period of 12 months from date of delivery, provided the HIU is installed by a qualified engineer within 6 months of date of delivery.

24 Months Parts Only - Parts proven to be defective will be supplied free of charge (for fitting by others) for a period of 24 months from date of delivery.

3. Replacement of parts under warranty does not extend the duration of the warranty.

4. Any other costs are not covered by this warranty. All other damages of any nature whatsoever and howsoever arising, are expressly excluded from this guarantee.

5. The warranty conditions above only apply:

a. In the UK only on items provided exclusively by Thermal Integration.
b. If the product is installed by a Thermal Integration approved engineer in compliance with the installation instructions.
c. The installer must complete the commissioning checklist in full at the time the HIU is installed. This checklist must be returned to Thermal Integration within 30 days of commissioning. Checklists are enclosed in the HIU installation instructions.
d. If the installation complies with all current and relevant building regulations and codes of practice. (including the requirement to clean the primary and secondary heating systems and add corrosion inhibitor in line with BS7593:2006)
e. If the product is used and maintained exclusively according to the manufacturer's instructions and proof of periodic inspection / maintenance by a Thermal Integration approved engineer is available.
f. If the returned item is accompanied by a fully completed Thermal Integration Warranty Return Form.

6. Excluded are defects caused by:

a. Failure to maintain in accordance with manufacturer’s instructions.
b. Improper use.
c. Any attempt at repairs / maintenance by un-qualified persons.
d. where parts other than Thermal Integration Genuine Parts have been used in any service or repair.
e. Lightning, fire or natural disasters.
f. Deterioration and / or pollution from the district heating system or water network, either domestic hot water or heating side.
g. PH values of the primary medium being less than 7.5 or greater than 9.0.
h. Harmful additives to the heating water.
i. Consumables as specified by us, including but not limited to: hoses, gaskets and batteries.

7. Report any faults to your installer, service engineer or Thermal Integration directly. Faulty parts must be accompanied by a fully completed Thermal Integration Warranty Return form, to be returned to Thermal Integration. Returned items remain the property of Thermal Integration Ltd.

The Thermal Integration Warranty Return Form can be requested by phone or email. Returns are not accepted unless expressly agreed in writing.
Transport risk of returned items lies with the sender. The shipping of replacement parts are the responsibility of the supplier.

8. If the HIU breaks down, we may ask you to pay us a deposit before we visit you to repair it. We will return the deposit in full if we find a fault that is covered by this warranty. We may keep the deposit if we cannot access your property at the time we had arranged with you to visit or we find other conditions of this warranty have not been met. A responsible adult must be at the property to give our engineer this access to the HIU.

Thermal Integration offer commissioning services across the UK. The service includes:

a. The fulfilment of the defined commissioning instructions.
b. Completion and return of site wide commissioning paperwork.
c. Rectification of any HIU problems.
d. Confirmation of HIU performance to contract specifications.
e. Engineer travel and subsistence.

Commissioning rates are charged on a whole day basis, and it is the responsibility of the client to ensure:

a. Safe access to properties and HIUs
b. Correct operation of central plant with delivery of heat to HIUs at specified temperatures, flow and pressures.
c. All pipework has been correctly tested and flushed.
d. Credit on billing system to enable security valve.

A minimum 2 weeks notice is required in writing to Thermal Integration before the requested commissioning date.

Technical assistance and engineer backup can be obtained by calling our offices:


The Heatweb Wiki website at contains information on all aspects of HIU design, function, and servicing, and is always the best place to visit for additional documentation or how to guides.

Country of Origin

This equipment is manufactured in the Netherlands by HSF B.V. and is supplied to Thermal Integration Ltd. In the UK. For all enquiries contact Thermal Integration Ltd. Tel: 08452 411 441

Warranty Returns Form

Returns Note.jpg

Thermal Integration Warranty Returns
Please return form together with the faulty part.

Return Address:-

Thermal Integration Ltd.

Windham Road,Chilton Industrial Estate,

Sudbury, Suffolk,

CO10 2XD.

For more information regarding our Guarantees and After Sales Backup for HIUs, please click HERE.