Bosch Worcester 28CDi User manual

24CDi, 28CDi & 35CDi II
COMBI
USER INSTRUCTIONS &
CUSTOMER CARE GUIDE
G.C. NUMBERS
APPLIANCE NATURAL GAS L.P.G.
24CDi Fanned Flued (RSF) 47 311 30 47 311 31
24CDi Balanced Flued (BF) 47 311 29
24CDi Open Flued (OF) 47 311 32 47 311 33
28CDi Fanned Flue (RSF) 47 311 34 47 311 35
35CDi II Fanned Flue (RSF) 47 311 58 47 311 59
Vote for your
‘Installer of the year’ at
www.worcester-bosch.co.uk
Worcester supports the
Benchmark code of practice

EXCELLENCE COMES
AS STANDARD
Thank you for purchasing a Worcester CDi gas-fired combi-
nation appliance.
The CDi appliances are made by Worcester and the strictest
quality control standards are demanded throughout every stage
of production.
Indeed, Worcester, part of the Bosch Group have led the
field in innovative appli-
ance design and perform-
ance for more than 40
years.
The result is
that your new Worcester
CDi appliance offers you
the very best of every-
thing - quality, efficiency,
economical running costs,
proven reliability and
value for money.
What’s more, you also have the assurance of our no-
nonsense 1 year parts and labour guarantee.
And, to keep your boiler operating at peak condition and
efficiency, an optional maintenance scheme is available from
Worcester. Contact our Service Contracts team on 01905 754624
for further details.
Page No.
Operating Instructions
.................................... 3-11
Fault and Breakdowns 12
Maintenance and
Extended Warranty
Information ............ 13-14
Guarantee Details .. 15-16
CONTENTS
2

GENERAL
INFORMATION
GAS SAFETY (INSTALLATION AND USE)
REGULATIONS 1998
It is the law, in GB, that all gas appliances must be installed by a
competent person in accordance with the above regulations. Failure
to install appliances correctly could lead to prosecution. It is in your
interest and that of safety to ensure compliance with the law. The
manufacturer’s notes must not be taken, in any way, as over-riding
statutory obligations.
In GB, a competent person is someone registered with CORGI.
All CORGI registered installers carry a CORGI ID card and have a regis-
tration number. Both should be recorded in the BENCHMARK check-
list. You can check that your installer is CORGI registered by calling
CORGI on 01256 372300.
WARNING: This appliance must be earthed and protected by a 3
amp fuse.
ELECTRICITY SUPPLY: 230V ~ 50Hz
IMPORTANT: To get the best from your Worcester CDi please read
these instructions carefully.
NOTE: In the event of a fault the appliance should not be used
until the fault has been corrected by a competent person.
BENCHMARK
The Benchmark initiative is a code of practice to encourage
the correct installation, commissioning and servicing of domestic cen-
tral heating boilers and system equipment.
A checklist can be found in the back of every installation
manual. This is a vital document that needs to be completed by the
installer at the time of installation. It confirms that the boiler has
been installed and commissioned according to the manufacturers
instructions.
In Eire the declaration found in IS 813 must be complet-
ed. Without completion of the checklist and/or declaration, manufac-
turers may refuse to respond to a call-out request. It is important that
the checklist and/or declaration are fully completed by your installer.
GENERAL DESCRIPTION
(See Fig.1.)
The WORCESTER CDi MODELS are combined domestic hot water
and central heating appliances. They consist of a gas fired boiler having
a varying output of between:
CH DHW
24CDi 9.0 - 24kW 9.0 - 24kW
28CDi 9.0 - 24kW 9.0 - 28kW
35CDi II 10.5 - 27.5kW 9.5 - 35.3kW
a heat exchanger to provide domestic hot water via the boiler, cir-
culating pump and water diverting valve. All the necessary controls to
provide mains fed domestic hot water and central heating.
The appliances are supplied as standard with a manual operating
switch. Alternatively a facia mounted programmer may have been fitted.
The appliances can operate in one of two modes. Hot water only or
hot water and central heating.
3

4
Hot Water Mode:
The appliance operates to supply only domestic hot water when
the heating temperature mode is fully anti-clockwise, at the –posi-
tion or the timer is programmed to OFF mode.
A flow restrictor is fitted within the appliance which limits a hot
water delivery rate to a maximum of:
24CDi 9.0 (±15%) litres/minute
28CDi 10.0 (±15%) litres/minute
35CDi II 12.0 (±15%) litres/minute
Hot Water and Central Heating mode:
When a demand is made
for heating by the system con-
trols (i.e. a programmer or
room thermostat), the pump
will energise, circulating pri-
mary water around the heat-
ing system and the burner
will light. The heat output
from the appliance in this
mode has been factory set to
maximum. The appliance will
operate as necessary to main-
tain the temperature of the
radiators at the level set by
the adjustment of the Heating
Temperature Control Knob.
(See Fig. 2.)
If the system no longer
requires output to maintain
the desired room tempera-
ture, the burner will extin-
guish. The pump will contin-
ue to run for a short period to
dissipate the residual heat
from the appliance and then
switch off.
The appliance will sup-
ply heat to the central heating
system as required. A demand
for hot water at a tap or show-
er will override the central
heating function for the peri-
od of the domestic hot water
demand.
Fig. 1. System Diagram.
Automatic air
vent
Gas to water
heat exchang-
er
Circulating
pump
Water to
water heat
exchanger
Diverter valve
CH
flow
Domestic
hot water
out
Domestic
cold sup-
ply
CH
return
Safety dis-
charge
Pressure
relief valve
Boiler
Expansion
vessel

5
CENTRAL HEATING SYSTEM
During the first few hours of operation of the central heating
system, check that all radiators are being heated at an even rate.
Should the upper area of a radiator be at a lower temperature than
the base of the radiator, it should be vented by releasing air through
the venting screw at the top of each radiator. Make sure your installer
shows you how to carry out the operation. Repeated venting will
reduce the quantity of water in the system and this must be replen-
ished for safe and satisfactory operation of the appliance. Should
water leaks be found in the system or excessive venting be required
from any radiator, your installer or heating engineer should be con-
tacted and the system corrected.
SEALED HEATING SYSTEM
The appliance can be fitted to a sealed heating sys-
tem which is pre-pressurised. In this case your installer
will advise you on the minimum and maximum pres-
sure that should be indicated on the pressure gauge. See
Fig. 2. Check regularly that this pressure is maintained
and contact your installer or maintenance engineer if
there is a permanent significant drop in pressure indi-
cated on the gauge. If the system loses pressure it
should be re-pressurised as instructed by the installer
(N.B. Maximum operating pressure 2.5 bar).
Re-pressurising The System (See Fig. 1a).
(If in doubt leave this procedure to your installer).
Remove the bottom panel to gain access to the fill-
ing loop assembly.
Insert the bayonet end of the filling key into the
corresponding cut outs in the filling loop housing and
twist to lock the key in place.
Turn the grey knob anti-clockwise to allow water
ingress and fill until the required pressure is reached.
Turn the grey knob clockwise to stop filling and
remove the filling key by lining up the bayonet end of
the key with the cut outs in the filling loop housing and
withdrawing the key.
N.B. The key must always be removed from the
filling loop housing after the system has been filled to
prevent accidental filling and to comply with Bylaw 14
of the Water Bylaws Scheme.
Store the key in a safe place for future use and
refit the bottom panel.
OPEN VENTED HEATING SYSTEM
The appliance may be fitted to an open vented
heating system your installer will advise you. There is
no need to observe the pressure gauge.
GENERAL NOTES
Fig. 1a.
Grey
Knob
Filling Key

6
CLEARANCES
Minimum clearances in millimetres.
Your installer will have provided adequate space around the
appliance for safety and servicing. Do not restrict this space by the
addition of cupboards, shelves etc. close to the appliance.
ROOM THERMOSTAT
A room thermostat may be fitted for control of the central heat-
ing temperature. It will be located in one room of the home. The
method of setting a room thermostat varies with the type and manu-
facture. Refer to the instructions supplied with the room thermostat.
THERMOSTATIC RADIATOR VALVES
If thermostatic radiator valves are fitted to the system then they
must conform to the requirements of BS2767. The radiator located in
the room where the room thermostat is sited must be controlled by a
thermostatic radiator valve.
SHOWERS, BIDETS, TAPS AND MIXING
VALVES
Standard hot and cold taps and mixing valves used with the
appliance must be suitable for operating at mains pressure.
Thermostatically controlled shower valves will guard against the flow
of water at too high a temperature.
If using a pressure equalising valve, set the Domestic Hot Water
temperature control knob to the ‘MAX’ position.
Hot and cold mains fed water can be supplied direct to an over-
rim flushing bidet subject to local water company requirements.
With all mains fed systems the flow of water from the individ-
ual taps will vary with the number of outlets operated simultaneous-
ly and the cold water mains supply pressure to the property. Flow bal-
ancing using ‘Ball-o-Fix’ type valves is recommended to avoid an
excessive reduction in flow to individual outlets.
For further information contact The Worcester Technical
Helpline. 08705 266241
HOT AND COLD FLOW
The flow of water demanded from both hot and cold service out-
lets is dependent upon mains supply, it may not be possible in some
installations to operate all outlets simultaneously.
WATER MAINS FAILURE
It is important to note that in the event of a mains water supply
failure, no tap water will be available until the mains supply is
restored. The appliance can still be used for heating provided that the
system is of the sealed system type. Open vent central heating sys-
tems should be turned off until the supply is restored.
USE IN HARD WATER AREAS
Normally there is no need for scale protection. However, in areas
of exceptionally hard water supply it is recommended that an In-Line
scale inhibitor be fitted.
Installation should be strictly in accordance with the require-
ments of the local Water Company. An isolating valve to facilitate
servicing should be incorporated.
24,28CDi RSF 35CDi II 24CDi OF 24CDiBF
Left-hand side 10 10 10 10
Right-hand side 10 10 10 10
In Front 600 600 600 600
Above 180 180 300 100
Below 200 200 200 200

7
The water hardness may be determined using the standard test
paper or by reference to the local Water Company.
Further information may be obtained from Worcester Bosch
Technical Helpline.
AIR SUPPLY FOR OPEN FLUED (O.F.)
APPLIANCES
Your installer will have made arrangements for an adequate sup-
ply of fresh air to the appliance. Fresh air is required for combustion.
Do not block up any air ways which may be let into a wall or door. Do
not hang clothes or other combustible materials over the appliance or
against the flue pipe.
NOTE: Do not place anything on top of the appliance. If the
appliance is fitted in a compartment do not use the compartment for
storage purposes unless it conforms to the requirements of
BS 6798:1987: Section 6. In particular, the flue pipe should not pass
through an airing cupboard space unless protected by a guard (such as
wire mesh) concentrically spaced 13mm (1/2in), as described in BS 6798:1987.
VENTILATION OF BALANCED FLUED (BF)
AND ROOM SEALED FANNED FLUE (RSF)
APPLIANCES
These are room sealed appliances and any ventilation openings
in a wall or door must not be obstructed. Do not allow the flue termi-
nal fitted on the outside wall to become obstructed or damaged.
NOTE: Do not place anything on top of the appliance. If the
appliance is fitted in a compartment do not use the compartment for
storage purposes unless it conforms to the requirements of
BS 6798:1987: Section 6. It is essential that the airing space is separat-
ed from the boiler space by a perforated non-combustible partition as
described in BS 6798:1987.
CIRCULATING PUMP
This may be fitted with a speed adjuster. If so it will be factory
set at maximum and should not be changed.
FROST PRECAUTIONS
If the appliance is not to be used for a long period of time and
there is a likelihood of freezing, then the appliance should be
drained. The Worcester Technical Helpline will advise you on suit-
able frost precautions. For short periods, the built-in frost protection
of the appliance will be adequate.
SERVICE
Annual servicing is important to ensure continuing high efficiency
and long life of your appliance. Suitable servicing arrangements should be
made with a competent third party. In the event of any difficulty in making
suitable service arrangements, Worcester personnel will be happy to dis-
cuss regular servicing and offer a comprehensive maintenance contract.
IMPORTANT: Do not touch or adjust any sealed compontent.
WARNING
If a gas leak exists, or is suspected, turn off the gas supply to the
appliance at the service cock and consult your local service engineer.
Do not touch any electrical switches to turn them either on or off.
Open all windows and doors. Do not smoke. Extinguish all naked
lights.
CLEANING
Do not use abrasive cleaners on the outer casing. Use a damp
cloth and a little detergent.

8
OPERATION OF
CONTROLS
OPERATING SWITCH
In the ‘’position there is no mains electricity to the
appliance.
In the ‘I’ position mains electricity is connected to the
appliance.
CENTRAL HEATING TEMPERATURE
CONTROL
The position of this knob will determine the temperature of the
water delivered to the radiators between the ‘I’ and ‘MAX’ position.
When the knob is turned anti-clockwise past the ‘I’ position towards
the ‘’(Summer Position), then the appliance will operate in the
HOT WATER mode only and no heat will be delivered to the radia-
tors.
DOMESTIC HOT WATER TEMPERATURE
CONTROL
The position of this knob will determine the temperature of the
water delivered at the domestic hot water taps between the ‘’and
the ‘MAX’ position.
By slightly reducing the flow of domestic water from the tap, the
delivery temperature of the water will be further increased. This is of
particular advantage in the winter, for example to increase bath water
temperature. Also this will provide an added advantage of reducing
the delay before hot water is obtained.
FACIA MOUNTED PROGRAMMER (if fitted)
Your installer may have mounted either a mechanical or an elec-
tronic programmer into the facia of your appliance. Operating instruc-
tions are supplied with the programmer.
RESET BUTTON
Press this button in for five seconds if any of the indicator lights
are flashing slowly.
SYSTEM PRESSURE GAUGE
The red needle has been set to show the sealed system pressure
which is required for the appliance to operate effectively. The grey
needle will show the actual pressure in the system. This does not
apply to any open vent system.

9
INDICATOR LIGHTS
Mains electricity indicator:
OFF : No mains electricity to the appliance
ON : Mains electricity is connected to the
appliance
Central heating demand indicator:
OFF : No demand for heat to the central
heating circuit
ON : Central heating demand
FLASHING SLOW : Ignition lockout
(once per second)
FLASHING FAST : Appliance fault (other than ignition
(five times per second) lockout)
Domestic hot water demand indicator:
OFF : No demand for domestic hot water
ON : Domestic hot water demand
FLASHING FAST : Air flow fault (RSF). Flue gas spillage
(OF)
(five times per second)
Central heating and domestic hot water demand indicators:
BOTH FLASHING SLOW : Overheat cut-off
(once per second)
Flame detection indicator:
OFF : Burner off
ON : Burner on
Fig. 2. Controls.
Operating
switch
Mains
electricity
indicator
Reset
button
Flame detection
indicator
DHW demand
indicator
Central heating
demand indicator
CH temperature
control knob
DHW temperature
control knob
Sealed system pressure
gauge

10
TO LIGHT THE APPLIANCE
Check that the water valves to the central heating circuit are open.
On sealed systems check that the grey needle on the pressure
gauge is not below the required pressure.
Switch on the mains electricity. The green power on indicator will
light. Set the room thermostat, if fitted, to maximum. Turn the central
heating temperature control knob to ‘MAX’. The red central heating
demand indicator will light.
The burner will light and the red flame detection indicator will light.
Set the central heating and hot water temperature control knobs
and the room thermostat, if fitted, to the desired temperature.
TO STOP THE APPLIANCE
For Short Periods
Turn the central heating temperature control knob fully anti-
clockwise to the ‘’position.
For Long Periods
Turn the operating switch to the ‘’position. Switch off the
mains electricity.
A facia mounted electronic programmer will retain its settings for
about two weeks, after which it will return to the factory set
programme. The display will disappear
after approximately 12 hours.
A facia mounted mechanical
programmer will require resetting once
the operating switch has been set to ‘O’,
or the mains supply has been
disconnected.
ELECTRICITY SUPPLY
FAILURE
If the electricity supply fails the
appliance will not operate. Once the
supply is restored the appliance will
return to normal operation. If a
programmer is fitted, check that the
settings have been maintained.
OVERHEAT CUT-OFF
THERMOSTAT
The appliance will enter a lockout
condition in the event of overheating.
An overheat cut-off thermostat is
fitted to the appliance which will
interrupt the electricity supply to the gas
valve.
If the overheat cut-off has operated,
both the central heating and the hot
water demand indicators will flash
together.
Fig. 3. CDi with front panel removed.
Circulating
pump
Clip
Locating peg
Expansion
vessel
Gas valve
TO LIGHT AND STOP THE
APPLIANCE

11
The appliance can be reset by pressing the reset button and
holding in for 5 seconds.
IGNITION LOCKOUT
The appliance will enter a lockout condition in the event of the
burner failing to ignite.
If the burner fails to light within a preset time of 10 seconds the
electricity supply to the gas valve will be interrupted.
If ignition lockout has occurred, the central heating demand
indicator will flash slowly (approximately once per second).
The appliance can be reset by pressing the reset button and
holding in for 5 seconds. Check that the gas supply has not been
interrupted.
If this condition continues to occur, then call a service engineer.
AIR FLOW DEVICE (RSF ONLY)
The appliance will enter a lockout condition in the event of an
air flow fault.
If the controls fail to detect the correct air flow through the
appliance the electricity supply to the gas valve will be interrupted.
If an air flow fault has occurred, the domestic water demand
indicator will flash (approximately five times per second).
The appliance will try to re-light after a waiting period of
approximately 4 minutes Check that the flue terminal has not been
obstructed or damaged. If this condition continues to occur, then call
a service engineer.
FLUE SPILLAGE DEVICE (OF ONLY)
The appliance is fitted with a device which detects the spillage
of combustion products from the draught diverter. In the event of the
flue becoming wholly or partly blocked this device will cut the gas
supply to the burner. If the device has activated, the D.H.W. demand
indicator will flash (approximately 5 times per second).
The device automatically resets after a waiting period of approxi-
mately 20 minutes. If the blockage remains the appliance will re-light
briefly before the device operates again. Should the problem persist
consult your service engineer.
REMOVAL AND REPLACEMENT
OF THE FRONT PANEL (See Fig. 3)
Removal:
Holding the panel at the edges, slide it upwards to disengage the
clips and ease the top edge forwards and upwards to raise it clear of
the two pegs on the top edge of the facia.
Replacement:
Locate the two holes in the bottom edge of the front panel over
the two pegs on the top edge of the facia and reverse the removal
procedure.
WARNING: Do not touch any component within the appliance
when it is running as some may be very hot.

12
A diagnostic system is provided which gives a flashing light dis-
play on the facia panel. Press the reset button to attempt to restart
the appliance. If the appliance does not return to normal operation
then contact your installer or Worcester Bosch.
More than 30% of all calls made to our contact centre reporting
appliance faults or breakdowns prove to be false alarms, as there is
often a simple explanation for the apparent malfunction.
So, to help you save time and money – not to mention frustration
and inconvenience – please refer to the General Information, Notes and
Lighting Instructions ensuring all controls are set correctly.
If, after following the instructions the appliance still fails to oper-
ate correctly call the Worcester Contact Centre on 08457 256206.
Arrangements will be made for an engineer to call as soon as possible.
CALL-OUT CHARGES
All of our field service engineers are factory trained.
If you request a visit from an engineer and your appliance has
been installed within the last 12 months, no charge will be made for
parts and/or labour, providing:
•The appliance was commissioned correctly on installation.
•An appliance fault is found and the appliance has been
installed within the past 12 months.
A call-out charge will be made where:
•The appliance has been installed for over 12 months, or
•Our Field Service Engineer finds no fault with the appliance
(see note), or
•The cause of breakdown is with other parts of your plumb-
ing/heating system, or with equipment not supplied by Worcester.
NOTE: Invoices for attendance and/or repair work carried out on
your appliance by any third party will not be accepted.
APPLIANCE FAILS TO
OPERATE

13
MAINTAINING YOUR
APPLIANCE
Your new Worcester CDi gas-fired appliance represents a
long-term investment in a reliable, high quality product.
In order to realise its maximum working life, and to ensure
it continues to operate at peak efficiency and performance, it is
essential that your boiler receives regular, competent servicing
and annual maintenance checks beyond the initial 12 month
guarantee period.
Regular service contracts can be arranged with your
installer – however if you have difficulty making a satisfactory
arrangement simply contact Worcester on 01905 754624 for
help.

CONTACT NUMBERS:
UK Contact Centre Tel. [phone]
UK Contact Centre Fax. [phone]
Scotland only Fax. [phone]
Eire Tel: [phone]
OPERATING HOURS:
Mon - Fri 7.00am to 8.00pm
Sat 8.00am to 5.00pm
Sun 9.00am to 12.00pm
Please contact our UK Contact Centre number where our friendly oper-
ators will book your call with one of our team of nationwide engineers.
NOTE:
Please refer to our website for our bank holiday opening hours.
www.worcester-bosch.co.uk
14
SERVICE CENTRES

15
YOUR WORCESTER
CDi COMBI
GUARANTEE
This appliance is guaranteed from the date of installation
subject to the following conditions & exceptions.
1. The appliance is guaranteed for a
period of 24 calendar months sub-
ject to the return of the guarantee
card within 30 days of installation
and the first 12 months service and
inspection having been carried out
to the satisfaction of BBT
Thermotechnology UK Ltd. Please
note that this service is not covered
under the terms & conditions of the
warranty and would therefore incur
a charge.
2. That during the period of this guar-
antee any components of the unit
which are Proved to be faulty or
defective in manufacture will be
exchanged or repaired Free of mate-
rial charges and free of labour
charges if repaired directly by BBT
Thermotechnology UK Ltd.
Invoices for attendance and repair
of this appliance by third parties
will not be accepted for payment by
BBT.
3. That the householder may be asked
to prove the date of installation and
that the appliance was correctly
commissioned. This information
must then be documented in the
Benchmark Gas Boiler
Commissioning Checklist.
4. That any product or part thereof
returned for servicing under the
guarantee must be accompanied by
a claim stating the model, serial
number and date of installation.
5. That BBT Thermotechnology UK Ltd
will not accept responsibility for
damage caused by faulty installa-
tion, neglect, misuse, accidental
damage or the non-observance of
the instructions contained in the
Installation and Users instructions
leaflets.
6. That the appliance has been used
only for normal domestic purposes,
for which it was designed.
7. That this guarantee applies only to
equipment purchased and used in
mainland Great Britain.
This guarantee is given in addition to all your normal statutory rights.
Worcester, Bosch Group is a trading name of BBT Thermotechnology UK Ltd.

8 716 114 647a (10/07)
GUARANTEE
REGISTRATION
You should complete and return the postpaid Guarantee
Registration Card within 30 days of purchase.
The card will register you as the owner of your new
Worcester CDi appliance and, while this will not affect your
statutory rights in any way, it will assist us to maintain an effec-
tive and efficient customer service by establishing a reference
and permanent record for your boiler.
IMPORTANT: SERIAL NUMBER. Copy the number off the
Guarantee Card.
FOR YOUR OWN RECORD
MODEL SERIAL NUMBER
(See identity label inside appliance casing)
TYPE/SIZE DATE OF INSTALLATION
CORGI CONTACT
All CORGI Registered installers carry a CORGI ID card and
have a registration number. Both should be recorded in your
central heating log book. You can check your installer is
CORGI Registered by calling CORGI on 01256 372300
Worcester, Bosch Group, Cotswold Way, Warndon, Worcester WR4 9SW.
Telephone: [phone] Fax: [phone].
Technical Helpline 08705 266241.
Worcester, Bosch Group is a trading name of BBT Thermotechnology UK Limited
www.worcester-bosch.co.uk