De Dietrich MS 24 FF: 5. DESCRIPTION OF BUTTON (Summer - Winter - Heating only - Off)

71

71.03982.03 - EN

OPERATING INSTRUCTIONS

4. ADJUSTING ROOM TEMPERATURE AND DHW TEMPERATURE

The system must be fitted with a room thermostat for controlling indoor temperature.

Adjust the room temperature (

) and the DHW temperature (

) by pressing the respective

+/-

(figure 1). The ignition 

of the burner is shown on the display with the symbol ( ) as described in section 3.

HEATING

While the boiler is operating in the heating mode, the display (figure 1) shows the flashing symbol (

) and the heating 

delivery temperature (°C).

DOMESTIC HOT WATER

While the boiler is operating in the DHW mode, the display (figure 1) shows the flashing symbol (

) and the DHW output 

temperature (°C).

Press this button to set the following operating modes:

• SUMMER

• WINTER

• HEATING ONLY

• OFF

In the 

SUMMER

 mode, the display shows  (

). The boiler satisfies requests for DHW only while central heating is NOT 

enabled (ambient frost protection function active).

In the 

WINTER

 mode, the display shows (

). The boiler satisfies requests for both DHW and central heating (am-

bient frost protection function active).

In the 

HEATING ONLY

 mode, the display shows (

). The boiler satisfies requests for central heating only (ambient frost 

protection function active).

In the 

OFF

 mode, the display shows neither of the above two symbols ( 

) (

). In this mode, only the ambient frost 

protection function is active while requests for DHW and central heating are not satisfied.

5. DESCRIPTION OF BUTTON   (Summer - Winter - Heating only - Off)

72

71.03982.03 - EN

OPERATING INSTRUCTIONS

To turn off the boiler, disconnect the electric power supply. In “OFF” mode (section 5) the boiler remains off (the display 

indicates OFF) though the electrical circuits remain live and the frost protection device is enabled (section 9).

7. TURNING OFF THE BOILER 8. GAS CONVERSION

The boilers can operate both on natural gas and 

LPG

.

All gas conversions must be made by an authorised Service Engineer.

WARNING

Disconnect the boiler from the mains power supply using the two-pole switch.

IMPORTANT:

 Regularly check that the pressure displayed on the pressure gauge is 0.7 - 1.5 bar, with the boiler cold. 

In case of overpressure, open the boiler drain tap. In case of insufficient temperature, open the boiler filling tap (figure 3).

Open the tap very slowly in order to vent the air.

6. FILLING THE SYSTEM

The boiler is fitted with a hydraulic pressure gauge which prevents the boiler from working if there is no water.

N.B.:

 In case pressure drops occur frequently, have the boiler checked by an authorised Service Engineer.

Figure 2

A -  

System drain tap 

B

 – Pressure gauge

C

 - System filling tap 

(supplied as an accessory for models 24 FF - 24)

D

 – Disconnector

CG_2262 / 1007_2901

24 MI FF - 24 MI

24 FF - 24 

73

71.03982.03 - EN

OPERATING INSTRUCTIONS

10. TROUBLESHOOTING

Do not drain the whole system as filling up with water again causes unnecessary and harmful scale to build up inside the 

boiler and the heating elements. If the boiler is not used during winter and is therefore exposed to the danger of frost, add 

some specific anti-freeze to the water in the system (e.g.: propylene glycol coupled with corrosion and scale inhibitors).

The electronic boiler management system includes a “frost protection” function for the heating system which, when delivery 

temperature falls below 5°C, operates the burner until a delivery temperature of 30°C is reached.

The frost protection function is enabled if:

*   the boiler is electrically powered;

*   the gas tap is open;

*   the system is at the correct pressure;

*   the boiler is not blocked.

9. PROLONGED SHUTDOWN. FROST PROTECTION

N.B.:

 in case of a fault, the display backlighting flashes together with the error code.

To keep the boiler efficient and safe, have it checked by the authorised Service Centre at the end of every operating period.

Careful servicing ensures economical operation of the system.

Do not clean the outer casing of the appliance with abrasive, aggressive and/or easily flammable cleaners (e.g.: petrol, 

alcohol, and so on). Always switch off the appliance before cleaning it (see section 7 Switching off the boiler).

11. ROUTINE MAINTENANCE INSTRUCTIONS

Faults are shown on the display with an error code (e.g.: E 01):

CODE 

DISPLAYED

FAULT

CORRECTIVE ACTION

E01

Failed ignition shutdown

Press and hold down “

R

” for at least 2 seconds. If this fault persists, call the 

Authorised Service Centre.

E02

Safety thermostat tripped

Press and hold down “

R

” for at least 2 seconds. If this fault persists, call the 

Authorised Service Centre.

E03

Flue thermostat/ flue pressure 

switch tripped

Call the Authorised Service Centre.

E04

Shutdown after 6 consecutive 

flame losses

Press and hold down “

R

” for at least 2 seconds. If this fault persists, call the 

Authorised Service Centre.

E05

Flow sensor failure

Call the Authorised Service Centre.

E06

DHW sensor fault

Call the Authorised Service Centre.

E10

Hydraulic pressure switch 

block

Check that the pressure in the system is correct; See section 6. If this fault 

persists, call the Authorised Service Centre.

E25/E26

Probable blocked pump safety 

trip

Call the Authorised Service Centre.

E35

Parasite flame (flame error)

Press and hold down “

R

” for at least 2 seconds. If this fault persists, call the 

Authorised Service Centre.

E96

Switching off due to reductions 

in power supply

RESET is automatic. If this fault persists, call the Authorised Service Centre

To RESET the boiler, press and hold down “R” for at 

least 2 seconds. If this fault persists, call the Authorised 

Service Centre.

N.B.:

 5 reset attempts can be performed after which 

the boiler shuts down. To reset again, switch off the 

boiler for a few seconds.

Figure 3

0607_1205

RESETTABLE

faults

74

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

This boiler has been designed to heat water to a temperature lower than boiling point at atmospheric pressure.

It must be connected to a central heating system and to a domestic hot water supply system according to its performance 

and power output.

Do the following before connecting the boiler:

a)  Make sure that the boiler is adjusted to use the type of gas delivered by the gas supply. To do this, check the markings 

on the packaging and the rating plate on the appliance.

b)  Make sure that the flue terminal draft is appropriate, that the terminal is not obstructed and that no exhaust gases 

from other appliances are expelled through the same flue duct, unless the latter has been specially designed to collect 

exhaust gas from more than one appliance, in compliance with current laws and regulations.

c)  Make sure that, if the boiler is connected to existing flue ducts, these have been thoroughly cleaned as residual products 

of combustion may detach from the walls during operation and obstruct the flow of fumes.

To ensure correct operation and maintain the warranty, observe the following precautions:

1.  DHW circuit:

1.1. 

If the water is harder than 20 °F (1 °F = 10 mg calcium carbonate per litre of water), install a polyphosphate dispenser 

or an equivalent treatment system, compliant with current regulations.

1.2. 

Thoroughly flush the system after installation of the appliance and before use.

1.3. 

The materials used for the product’s DHW circuit comply with Directive 98/83/CE.

2.  Heating circuit

2.1. new system

Before proceeding with installation of the boiler, the system must be cleaned and flushed to eliminate residual 

thread-cutting swarf, solder and any solvents, using suitable proprietary products. To avoid damaging metal, plastic 

and rubber parts, only use neutral cleaners, i.e. non-acid and non alkaline. Recommended cleaning products are:

SENTINEL X300 or X400 and FERNOX Regenerator for heating circuits. Use these products in strict compliance 

with the manufacturers’ instructions.

2.2. existing system:

Before installing the boiler, drain the system and clean it to remove sludge and contaminants, using suitable 

proprietary products as described in section 2.1.

To avoid damaging metal, plastic and rubber parts, use only neutral cleaners, i.e. non-acid and non-alkaline such 

as SENTINEL X100 and FERNOX Protector for heating circuits. Use these products in strict compliance with the 

manufacturers’ instructions.

Remember that the presence of foreign bodies in the heating system can adversely affect boiler operation (e.g. 

overheating and excessive noise of the heat exchanger).

Failure to observe the above will render the warranty null and void

.

The following notes and instructions are addressed to fitters to allow them to carry out trouble-free installation. Instructions 

for igniting and using the boiler are contained in the ‘Instructions for Users’ section.

•   This boiler can be connected to any type of double- or single-pipe convector plate, radiator or thermoconvector. Design 

the system sections as usual, though, bearing in mind the available flow-head at the plate, as shown in section 25.

•   Do not leave any packaging (plastic bags, polystyrene, etc.) within reach of children, as it is a potential source of danger.

•   Initial lighting of the boiler must be carried out by an authorised Service Engineer, as indicated on the attached sheet.

Failure to observe the above will render the guarantee null and void.

ADDITIONAL PUMP WARNING

If an additional pump is used on the heating system, position it on the boiler return circuit. This will allow the correct 

operation of the water pressure switch.

SOLAR WARNING

if the instantaneous (mixed) boiler is connected to a system with solar panels, the maximum temperature of the domestic 

hot water entering the boiler must not exceed 

60°C

.

12. GENERAL INFORMATION 13. INSTRUCTIONS PRIOR TO INSTALLATION

75

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

13. INSTALLAZIONE DELLA CALDAIA  14. INSTALLING THE BOILER 

After deciding the exact location of the boiler, make sure there is sufficient room to perform maintenance operations (at 

least 450 mm of headroom is required in order to replace the expansion vessel).

Connect the system to the gas and water inlets present on the lower bar of the template. Fit two G3/4 taps (flow and 

return) on the central heating circuit; these taps make it possible to carry out important operations on the system without 

draining it completely. If you are either installing the boiler on an existing system or replacing one, as well as the above, 

fit a settling tank under the boiler on the system return line in order to collect any deposits and scale circulating in the 

system after flushing. After fixing the boiler to the template, connect the flue and air ducts, supplied as accessories, as 

described in the following sections.

If the model 

24 MI - 24

 natural draught boiler is installed, connected it to the flue with a metal pipe resistant to normal 

mechanical stress, heat, products of combustion and relative condensate.

IMPORTANT

After filling the boiler, vent the entire internal circuit and the system as follows:

•  close the gas on-off valve;

•   power the boiler.

•   open the vent valve on the pump body;

•   press (

) to set the boiler in the “WINTER” operating mode;

•   send a heat demand from the room thermostat;

•   open a hot water tap to alternate CH demand with DHW demand;

•   after a few ignition attempts the boiler will shut down (error E01 appears on the display);

•   to rest, press and hold down “

R

” for at least 2 seconds;

•   repeat the procedure at least another two times;

•   close the vent valve.

After venting the boiler circuit, proceed with initial lighting.

EXPANSION VESSEL

The boiler features a standard 6-litre expansion vessel with a pre-charge pressure of 1 bar. The maximum volume of water in 

the system is calculated according to hydrostatic pressure at an average water temperature of 80°C (flow: 95°C return: 75°C).

Hydrostatic pressure (m)

5

6

7

8

9

10

Maximum system volume (l)

110

105

95

85

77

70

76

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

14. DIMENSIONI CALDAIA  15. DIMENSIONS OF BOILER 

Figure 5

24 FF - 24 MI FF

24 - 24 MI

CG_2009 / 1006_1802

CG_2009 / 1006_1803

G”3/4 HEATING FLOW

G”1/2 DOMESTIC HOT WATER OUTLET

G”3/4 HEATING RETURN

G”1/2 DOMESTIC COLD WATER INLET

G”3/4 GAS INLET TO BOILER

G”3/4 STORAGE BOILER COIL FLOW

WARNING

Tighten the boiler nipple water connections with care (maximum tightening torque 30 Nm).

Figure 4

24 MI - 24 MI FF

24 - 24 FF 

CG_2263 / 1007_1403

77

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

16. INSTALLING THE FLUE AND AIR DUCTS

Model 24 MI FF - 24 FF 

The boiler is easy and flexible to install thanks to the ex-

tensive range of available accessories, as described below.

The boiler has been designed for connection to a vertical 

or horizontal coaxial flue-air duct. A splitting kit is also 

available if separate ducts are required.

Only accessories supplied by the manufacturer must 

be used for installation!

WARNING: To optimise operating safety, make sure 

the flue ducts are firmly fixed to the wall with suitable 

brackets.

Figure 6

0503_0905/CG1638

… COAXIAL FLUE-AIR DUCT (CONCENTRIC)

This type of duct is used to discharge exhaust fumes and draw combustion air both outside the building and if a LAS flue 

is fitted.

The 90° coaxial curve allows the boiler to be connected to a flue-air duct in any direction as it can be rotated by 360°. It 

can also be used as a supplementary curve combined with a coaxial duct or a 45° curve.

If fumes are discharged outside the building, the flue-air duct 

must protrude at least 18 mm from the wall to allow an alu-

minium weathering surround to be fitted and sealed to avoid 

water infiltrations.

Make sure there is a minimum upward slope towards the 

outside of 1 cm per metre of duct.

•

A 90° curve reduces total duct length by 1 metre.

•

A 45° curve reduces total duct length by 0.5 metres.

The first 90° curve is not considered when calculating the 

maximum available length.

Figure 7

0805_2901 / C

G_2073

Connector

Boiler model

Length (m)

Use of DIAPHRAGM 

on INLET LINE

A

24 MI FF

24 FF

0 ÷ 1

Yes

1 ÷ 4

No

78

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

16.1 HORIZONTAL FLUE INSTALLATION EXAMPLES

16.2 LAS FLUE DUCT INSTALLATION EXAMPLES C42 TYPE

16.3 VERTICAL FLUE INSTALLATION EXAMPLES

This type of installation can be carried out on either a flat or a pitched roof by fitting a flue terminal and a special weathering 

surround with sleeve (both available on request).

0503_0908/CG1641

0503_0907/CG1640

0512_2001

For detailed installation instructions, consult the technical data provided with the accessories.

L max = 9 m (Ø 80/125 mm)

L max = 4 m (Ø 60/100 mm)

10 m (Ø 80/125 mm)  

L max = 4 m (Ø 60/100 mm)

10 m (Ø 80/125 mm)

L max = 4 m (Ø 60/100 mm)

10 m (Ø 80/125 mm)

L max = 3 m (Ø 60/100 mm)

9 m (Ø 80/125 mm)

L max = 3 m (Ø 60/100 mm)

9 m (Ø 80/125 mm)

L max = 7 m (Ø 80/125 mm)

L max = 8 m (Ø 80/125 mm)

79

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

… SEPARATE FLUE AND AIR DUCTS

This type of installation makes it possible to discharge exhaust fumes both outside the building and into single flue ducts. 

Comburent air can be drawn in at a different location from that of the flue terminal. The splitting kit comprises a flue duct 

adaptor (100/80) and an air duct adaptor. For the air duct adaptor, fit the screws and seals previously removed from the cap.

The 90° curve allows the boiler to be connected to a flue-air duct in any direction as it can be rotated by 360°. It can also 

be used as a supplementary curve combined with a duct or a 45° curve.

•   A 90° curve reduces total duct length by 0.5 metres.

• A 45° curve reduces total duct length by 0.25 metres.

The first 90° curve is not considered when calculating the maximum available length.

Boiler model

(L1+L2)

Position 

of air regulator

    CO

2

 %

G20

G31

24 MI FF

24 FF

0 ÷ 4

1

7,2

8

4 ÷ 18

2

18 ÷ 30

3

Adjusting the air regulator for sepa-

rate flues

This regulator must be adjusted to 

optimise combustion efficiency and 

parameters.

After turning the air intake connecter, 

which can be mounted both to the right 

and the left of the exhaust flue duct, 

suitably adjust the excess air according 

to the total length of the combustion 

exhaust and inlet flue ducts.

Turn this regulator anticlockwise to de-

crease the excess of comburent air and 

vice-versa to increase it.

To fine tune, use a combustion product 

analyser to measure the amount of CO

2 

in the fumes at maximum heat capacity, 

and, if a lower value is measured, gra-

dually adjust the air regulator until the 

amount of CO

2

 indicated in the following 

table is measured.

To mount this device correctly, consult 

the relative instructions

.

Figure 8

0809_0201 / CG_2045

Flue duct adaptor

Connector

Air intake restrictor

80

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

16.5 HORIZONTAL SEPARATE FLUE INSTALLATION EXAMPLES - C82

IMPORTANT

 -

 Make sure there is a minimum downward slope towards the outside of 1 cm per metre of duct length. 

In the event of installation of the condensate collection kit, the angle of the drain duct must be directed towards the boiler.

N.B.:

For the C52 type, do not fit the flue and air duct terminals on opposite walls of the building.

The inlet flue must have a maximum length of 10 metres for C52 fumes outlets. 

If the discharge duct is longer than 6 metres, install the condensate collection kit, supplied as an accessory, near the boiler

16.4 DIMENSIONS OF SEPARATE OUTLETS

CG_2124 / 0905_2305

L max = 10 m   

(L1 + L2) max  = 30 m   

1010_0102/CG1643

CG_1643_FR / 1010_0101

IMPORTANT:

 if fitting a single flue duct, make sure it is adequately insulated (e.g.: with glass wool) wherever the duct 

passes through building walls. For detailed installation instructions, consult the technical data provided with the accessories.

81

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

17. ELECTRICAL CONNECTIONS 18. CONNECTING THE ROOM THERMOSTAT

•   Access the power supply terminal block (figure 9) as described in the previous section;

•   remove the jumper on terminals (1) and (2);

•   thread the two-wire cable through the grommet and connect it to these two terminals.

This machine is only electrically safe if it is correctly connected to an efficient earth system in compliance with current 

safety regulations.

Connect the boiler to a 230V single-phase earthed power supply using the supplied three-pin cable, observing correct 

LIVE-NEUTRAL polarity.

Use a double-pole switch with a contact separation of at least 3 mm

. When replacing the power supply cable, fit a 

harmonised HAR H05 VV-F’ 3x0.75mm

2

 cable with a maximum diameter of 8 mm.

…Access to the power supply terminal block

•   disconnect the boiler from the mains power supply using the two-pole switch;

•   remove the two screws fixing the control panel to the boiler;

•   rotate the control panel;

•   remove the cover and access the wiring area (figure 9).

The 2A fast-blowing fuse is incorporated in the power supply terminal block (to check and/or replace the fuse, pull out 

the black fuse carrier).

IMPORTANT:

respect polarity 

L

 (LIVE) -

N

 (NEUTRAL).

(L) = 

Live

 (brown)

(N) = 

Neutral

 (blue)

    = 

Earth

 (yellow-green)

(1) (2) =   

Contact for room thermostat

CG_2008 / 1009_0301

Figure 9

82

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

19. GAS CONVERSION

The authorised Technical Assistance Service can convert this boiler to natural gas (

G. 20

) or liquid gas (

G.31

). 

Carry out the following operations:

A) replace the nozzles of the main burner and the gas diaphragm (if fitted); 

B)  new max. and min. calibration of the pressure regulator.

A) Replace the burner nozzles

•   carefully pull the main burner off its seat;

•   replace the main burner nozzles making sure to fully tighten them to prevent gas leaks. Nozzle diameters are specified 

in table 2.

B) Calibrate the pressure regulator

•   connect the positive pressure test point of a differential pressure gauge (possibly water-operated) to the gas valve 

pressure test point (

Pb

) (Figure 10). Only for models with sealed chambers, connect the negative pressure test point of 

the manometer to a “T” fitting in order to join the boiler adjustment outlet, the gas valve adjusting outlet (Pc) and the 

pressure gauge. (The same measurement can be made by connecting the pressure gauge to the pressure test point 

(

Pb

) after removing the front panel of the sealed chamber);

  Measuring burner pressure using methods other than those described could lead to incorrect results as the low pressure 

created by the fan in the sealed chamber would not be taken into account.

B1) Adjustment to nominal heat output:

•   open the gas tap and switch the boiler to the Winter mode;

•   open a hot water tap that can provide a flow rate of at least 10 litres a minute or make sure there is maximum heat 

demand;

•   remove the modulator cover;

•   adjust the tube brass screw (a) until the pressure values shown in table 1 are obtained;

make sure that the dynamic inlet pressure of the boiler, measured at the gas valve pressure test point (Pa) (Figure 10) is 

correct (37 mbar for propane or 20 mbar for natural gas).

B2) Adjustment to reduced heat output:

•   disconnect the modulator power cable and unscrew the screw (b) until a pressure value corresponding to reduced heat 

output is achieved (see tab. 1);

•   reconnect the cable;

•   mount the modulator cover and seal.

B3) Final checks

•   attach the additional plate supplied with the transformer, specifying the type of gas and the calibration performed.

Figure 10

gas valve 

mod. SIGMA 845

b

a

0605_1502

Figure 11

CG_2273 / 1008_2602

gas diaphragm

ATTENTION

If the natural gas inlet pressure is too low (less than 17 mbar) remove the gas diaphragm installed over the gas valve (fig. 

10) and set parameter 

F02=00

 on the electronic board (§21). 

83

71.03982.03 - EN

INSTALLATION INSTRUCTIONS

19.1 GAS VALVE CALIBRATION FUNCTION

Note:

The function is automatically deactivated after a period of 15 minutes, at the end of which the electronic board returns to 

its operating status prior to the activation of the function or prior to reaching the set maximum temperature.

To simplify calibration of the gas valve, the calibration function may be set directly 

on the boiler control panel as follows:

a)

 hold down the buttons 

 and 

 together for at least 6 seconds; 

b)

 after about 6 seconds, the symbols 

 flash;

c)

  the display shows, at intervals of one second, “

100

” and the 

flow temperature

.

  In this phase, the boiler works at the maximum heating output (100%). 

d)

 press 

+/-

   to immediately set the power of the boiler (100% or 0%);

e)

  adjust the 

“Pmax/Pmin”

 screw (figure 10) to set the burner pressure value as 

described in table 1.

  To adjust pressure at maximum power, turn the “

Pmax

” screw (fig. 10) clockwise 

to increase or anti-clockwise to decrease pressure at the burner.

  To adjust pressure at minimum power, turn the “

Pmin

” screw (fig. 10) clockwise 

to increase or anti-clockwise to decrease pressure at the burner.

f)

 press 

+/-

 to gradually set the desired power level (interval = 1%).

Press the button   to leave the function.

0805_2302 / 1002_1201

Consumption 15°C-1013 mbar

24 MI FF - 24 FF

24 - 24 MI

G20

G31

G20

G31

Rated power

2,80 m

3

/h

2,00 kg/h

2,80 m

3

/h

2,04 kg/h

Reduced power

1,12 m

3

/h

0,82 kg/h

1,12 m

3

/h

0,82 kg/h

p.c.i.

34,02 MJ/m

3

46,34 MJ/kg

34,02 MJ/m

3

46,34 MJ/kg

Table 2

* 1 mbar = 10,197 mmH

2

O

Table of burner nozzles

24 MI FF - 24 FF

24 - 24 MI

gas type

G20

G31 

G20

G31

diameter of nozzles (mm)

1,28

0,77 

1,18

0,77

Burner pressure (mbar*)

REDUCED HEAT OUTPUT

2,0

5,7

2,4

5,6

Burner pressure (mbar*)

RATED HEAT OUTPUT

11,6

32,6

13,8

31,0

Diameter of gas diaphragm (mm)

4,8

—

5,5

—

N° nozzles

13

Table 1