MTH 350 OT - Boiler AEG - Free user manual and instructions

Product Type	Gas Boiler (Condensing)
Brand	AEG
Model	MTH 350 OT
Energy Source	Natural Gas / LPG
Heating Output	24 kW
Domestic Hot Water Output	30 L/min (ΔT 30°C)
Dimensions (HxWxD)	700 x 400 x 300 mm
Weight	30 kg
Power Supply	230 V / 50 Hz
Electrical Protection Rating	IPX4D
Efficiency	Up to 94% (condensing)
Flue Type	Room-sealed (balanced flue)
Control Interface	Electronic control panel with LCD display
Safety Features	Frost protection, pump anti-seize, overheat protection, flame failure detection
Installation Type	Wall-hung
Noise Level	< 50 dB(A)
Water Connection	3/4 inch (heating and DHW)
Maintenance	Annual servicing required
Spare Parts Availability	Available via AEG authorized dealers

Frequently Asked Questions - MTH 350 OT AEG

How do I reset the AEG MTH 350 OT boiler after a fault?

Locate the reset button on the control panel. Press and hold for 5 seconds until the display shows normal operation. If the fault persists, consult the manual or call a technician.

What type of gas does the MTH 350 OT use?

The boiler is designed for natural gas but can be converted to LPG using a conversion kit. Refer to the installation manual for instructions.

How often should I service the AEG MTH 350 OT boiler?

Annual servicing by a qualified Gas Safe registered engineer is recommended to ensure safe and efficient operation.

What does error code E01 mean on the display?

Error E01 typically indicates a flame failure. Check gas supply and ignition components. If the issue persists, contact a technician.

Can I install the MTH 350 OT myself?

No. Installation must be carried out by a certified professional in accordance with local regulations. Incorrect installation can lead to safety hazards.

What is the maximum heating output of the boiler?

The heating output is adjustable up to 24 kW, depending on system requirements.

How do I adjust the hot water temperature?

Use the temperature control knob on the front panel. Turn clockwise to increase temperature, counterclockwise to decrease. The set temperature appears on the display.

What does the frost protection feature do?

The boiler automatically activates the pump and burner when the temperature drops near freezing to prevent damage to the system.

Where can I find spare parts for the MTH 350 OT?

Spare parts are available through AEG authorized service centers and selected online retailers. Provide the model number when ordering.

Why is the boiler making a banging noise?

Banging noises may indicate air in the system or kettling due to limescale. Bleed radiators or descale the heat exchanger. If persistent, call a technician.

USER MANUAL MTH 350 OT AEG

Hydraulically controlled, open vented small instantaneous water heater with bare wire heating system

Operation and installation 23

Mounting the fitting

Check the protective conductor

1. General information 25
2. Safety 26
3. Appliance description......27
4. Settings.....27
5. Cleaning, care and maintenance 27
6. Troubleshooting 28

INSTALLATION

1. Safety 29
2. Appliance description....29
3. Preparations....30
4. Installation....30
5. Commissioning....34
6. Shutting down....34
7. Troubleshooting 34
8. Maintenance....35
9. Specification 36

GUARANTEE

ENVIRONMENT AND RECYCLING

SPECIAL INFORMATION

The appliance may be used by children aged 3 and up and persons with reduced physical, sensory or mental capabilities or a lack of experience and know-how, provided that they are supervised or they have been instructed on how to use the appliance safely and have understood the resulting risks. Children must never play with the appliance. Children must never clean the appliance or perform user maintenance unless they are supervised.

During operation, the tap can reach temperatures in excess of 50 °C. There is a risk of scalding at outlet temperatures in excess of 43 °C.

Special information

• Ensure the appliance can be separated from the power supply by an isolator that disconnects all poles with at least 3 mm contact separation.
• The specified voltage must match the mains voltage. • The power cable must only be replaced (for example if damaged) by a qualified contractor authorised by the manufacturer, using an original spare part. • Fix the appliance in position as described in chapter „Installation / Preparations“.
• Observe the maximum permissible pressure (see chapter „Installation / Specification / Data table“).
• The specific water resistivity of the mains water supply must not be undershot (see chapter „Installation / Specification / Data table“).

- Drain the appliance as described in chapter „Installation / Maintenance / Draining the appliance“.

OPERATION

1. General information

The chapter „Operation“ is intended for appliance users and qualified contractors.

The chapter „Installation“ is intended for qualified contractors.

Note

Read these instructions carefully before using the appliance and retain them for future reference.

Pass on the instructions to a new user if required.

1.1 Safety instructions

1.1.1 Structure of safety instructions

KEYWORD Type of risk

Here, possible consequences are listed that may result from failure to observe the safety instructions.

» Steps to prevent the risk are listed.

1.1.2 Symbols, type of risk

Symbol Type of risk
	Injury
	Electrocution
	Burns(burns, scalding)

1.1.3 Keywords

KEYWORD Meaning
DANGER	Failure to observe this information will result in serious injury or death.
WARNING	Failure to observe this information may result in serious injury or death.
CAUTION	Failure to observe this information may result in non-serious or minor injury.

1.2 Other symbols in this documentation

Note

Notes are bordered by horizontal lines above and below the text. General information is identified by the symbol shown on the left.

» Read these texts carefully.

Operation

Symbol
	Material losses(appliance damage, consequential losses and environmental pollution)
	Appliance disposal

» This symbol indicates that you have to do something. The action you need to take is described step by step.

1.3 Units of measurement

Note Unless specified otherwise, all dimensions are given in mm.

2. Safety

2.1 Intended use

This appliance is intended for domestic use. It can be used safely by untrained persons. The appliance can also be used in a non-domestic environment, e.g. in a small business, as long as it is used in the same way.

This appliance is designed to heat DHW. The appliance is designed for one hand washbasin.

Any other use beyond that described shall be deemed inappropriate. Observation of these instructions and of instructions for any accessories used is also part of the correct use of this appliance.

2.2 General safety instructions

DANGER Scalding

During operation, the tap can reach temperatures in excess of 50 °C. There is a risk of scalding at outlet temperatures in excess of 43 °C.

WARNING Injury

The appliance may be used by children aged 3 and up and persons with reduced physical, sensory or mental capabilities or a lack of experience and know-how, provided that they are supervised or they have been instructed on how to use the appliance safely and have understood the resulting risks. Children must never play with the appliance. Children must never clean the appliance or perform user maintenance unless they are supervised.

DANGER Electrocution

Any damaged power cables must be replaced by a qualified electrician. This prevents potential hazards from arising.

Material losses

Protect the appliance and tap against frost.

Material losses

Ensure that the non-pressurised appliance is not exposed to any pressure as this could cause irreparable damage:

» Only use the special aerator provided. » Never use aerators or hoses with aerators. » Never seal the tap outlets. » Prevent scale build-up at the tap outlets (see chapter "Cleaning, care and maintenance").

2.3 Test symbols

See type plate on the appliance.

3. Appliance description

The hydraulically controlled, non-pressurised small instantaneous water heater heats the water directly at the draw-off point. The heating system starts automatically when the tap is opened. The short pipe runs ensure that energy and water losses are minimal.

The DHW output depends on the cold water temperature, the heating output and the flow rate.

The bare wire heating system is suitable for hard and soft water areas. This heating system has a low susceptibility to scale build-up. The heating system ensures quick and efficient DHW provision at the hand washbasin.

Fitting the special aerator supplied provides an optimum water jet.

4. Settings

The appliance heating system switches on automatically as soon as you open the DHW valve at the tap or activate the sensor of a sensor tap. The water is heated. The water temperature can be adjusted at the tap:

For the start volume, see chapter „Specification / Data table / On“.

Increasing the temperature

» Reduce the flow rate at the tap.

Reducing the temperature

» Open the tap further or add more cold water.

Following an interruption of the water supply

See chapter "Commissioning / Recommissioning".

5. Cleaning, care and maintenance

Never use abrasive or corrosive cleaning agents. A damp cloth is sufficient for cleaning the appliance.

Material losses

Scale build-up at the tap outlets can put the appliance under pressure and may cause irreparable damage.

Check the taps/valves regularly. Limescale deposits at the spouts can be removed using commercially available descaling agents.

Operation

Have the electrical safety of the appliance regularly checked by an electrician. Regularly descale or replace the special aerator (see chapter "Appliance description / Accessories").

6. Troubleshooting

Problem Cause Remedy
The appliance will not start despite the DHW valve being fully open.	No power to the ap- pliance.	Check the fuses/ MCBs in your fuse box.
	The aerator in the tap is scaled up or dirty.	Clean and/or descale the aerator or replace the special aerator.
	The water supply has been interrupted.	Vent the appliance and the cold water inlet line (see chapter "Settings").

If you cannot remedy the fault, notify your qualified contractor. To facilitate and speed up your enquiry, please provide the serial number from the type plate (000000 / 0000-00000).

Only a qualified contractor should carry out installation, commissioning, maintenance and repair of the appliance.

7.1 General safety instructions

We guarantee trouble-free function and operational reliability only if original accessories and spare parts intended for the appliance are used.

Material losses

Observe the max. permissible inlet temperature. Higher temperatures may damage the appliance. You can limit the inlet temperature by means of a central thermostatic valve.

Material losses

Only operate the appliance with non-pressurised taps.

7.2 Instructions, standards and regulations

Note

Observe all applicable national and regional regulations and instructions.

The specific electrical resistance of the water must not fall below that stated on the type plate. In a linked water network, factor in the lowest electrical resistance of the water (see chapter „Specification / Data table“). Your water supply utility will advise you of the specific electrical water resistance or conductivity.

8. Appliance description

8.1 Standard delivery

The following are delivered with the appliance:

• Sieve inside the cold water inlet • Special aerator „SR“ • Company logo for oversink installation

Installation

8.2 Accessories

Special aerator „SR“*

SR 3: Part number 289591 for MTH 350 and MTH 440

- SR 5: Part number 270582 for MTH 570

* For use in thread M22/M24.

Non-pressurised taps

• AHo 40 MTH - non-pressurised wall mounted tap
• AHu 40 MTH - non-pressurised twin lever basin tap
• AHEu 40 MTH - non-pressurised mono lever basin tap

9. Preparations

» Flush the water line thoroughly.

Water installation

A safety valve is not required.

Taps

» Use suitable taps (see chapter „Appliance description / Accessories“).

Note

Fitting the special aerator supplied provides an optimum water jet.

10. Installation

10.1 Installation site

Install the appliance in a room free from the risk of frost and near the draw-off tap.

Ensure that the lateral fixing screws for the cover are always accessible.

The appliance is suitable for undersink installation (water connections at the top) and oversink installation (water connections at the bottom).

DANGER Electrocution

Protection rating IP25 is only ensured if the appliance back panel is fitted.

» Always fit the appliance back panel.

10.2 Installation options

10.2.1 Undersink installation, non-pressurised, with non-pressurised tap

10.2.2 Appliance installation

» Mount the appliance on the wall.

Note

The wall must have a sufficient load-bearing capacity.

Undo the cover fixing screws by two turns. Undo the snap fastener using a screwdriver. Remove the appliance cover with the heater towards the front.

Installation

Using pliers, break out the knock-out for the power cable in the appliance cover. Correct the contours with a file if necessary. Use the appliance back panel as a drilling template. Secure the appliance back panel to the wall with suitable rawl plugs and screws.

Route the power cable through the cable entry in the back panel. Hook in the appliance cover with the heater at the bottom. Click the heater into place using the snap fastener. Secure the appliance cover with the cover fixing screws.

Tap installation

Material losses

When making the connections, counter the torque on the appliance using a size 14 spanner.

Install the tap. For this, also observe the tap operating and installation instructions.

10.2.3 Oversink installation, non-pressurised, with non-pressurised tap

Tap installation

Install the tap. For this, also observe the tap operating and installation instructions.

Material losses

When making the connections, counter the torque on the appliance using a size 14 spanner; see chapter "Installation alternatives / Under-sink installation".

Appliance installation

Fit the appliance to the tap with the water connections.

10.3 Connecting the power supply

DANGER Electrocution

Carry out all electrical connection and installation work in accordance with regulations.

DANGER Electrocution

Ensure that the appliance is earthed.

Ensure the appliance can be separated from the power supply by an isolator that disconnects all poles with at least 3 mm contact separation.

DANGER Electrocution

The appliances are delivered with a power cable (MTH 350 with plug).

Connection to a permanent power supply is possible, provided the fixed cable has a cross-section that is at least equal to that of the standard power cable of the appliance. A maximum cross-section of 3 × 6 mm² may be used.

If the appliance is installed over the sink, route the power cable behind the appliance.

Material losses

When making the connection to a standard safety socket (in the case of a power cable with plug), ensure that the socket is freely accessible after the appliance has been installed.

Material losses

Take note of the type plate. The specified voltage must match the mains voltage.

Installation

Connect the power cable as shown in the wiring diagram (see chapter "Specification / Wiring diagram").

11. Commissioning

11.1 Initial start-up

26_02_05_0087

Fill the appliance by running the tap several times until the pipework and appliance are free of air. Carry out a tightness check. Insert the power cable plug, if present, into the standard safety socket or set the fuse/MCB. Check the function of the appliance. In the case of oversink installation, affix the company logo supplied over the existing company logo.

11.2 Appliance handover

Explain the appliance function to users and familiarise them with its operation. Make users aware of potential dangers, especially the risk of scalding. Hand over these instructions.

11.3 Recommissioning

Material losses

Following an interruption of the water supply, recommission the appliance by carrying out the following steps, in order to prevent irreparable damage to the bare wire heating system.

Isolate the appliance from the power supply. Pull the power cable plug, if present, from the socket, or remove the fuse/reset the MCB. See chapter "Initial start-up".

12. Shutting down

» Isolate the appliance from the power supply by means of the fuse/MCB in your fuse box or by pulling the power cable plug from the socket. » Drain the appliance (see chapter "Maintenance").

13. Troubleshooting

Problem Cause Remedy
The appliance will not start despite the DHW valve being fully open.	The aerator in the tap is scaled up or dirty.	Clean and/or descale the aerator or replace the special aerator.
	The sieve in the cold water line is blocked.	Clean the sieve after shutting off the cold water inlet line.
	The heater is faulty.	Check the resistance of the heating system and replace the appliance if required.

14. Maintenance

DANGER Electrocution Before any work on the appliance, disconnect all poles from the power supply.

Draining the appliance

DANGER Scalding Hot water may escape during the draining process.

If the appliance needs to be drained for maintenance or to protect the whole installation when there is a risk of frost, proceed as follows:

» Close the shut-off valve in the cold water inlet line. » Open the draw-off valve. » Undo the water connections on the appliance.

Cleaning the strainer

You can clean the fitted strainer after removing the cold water supply pipe.

Checking the earth conductor

» Check the earth conductor (in Germany e.g. BGV A3) on the earth conductor contact of the power cable and on the appliance connector.

Appliance storage

» Store the dismantled appliance in a room free from the risk of frost, as water residues remaining inside the appliance can freeze and cause damage.

Replacing the power cable for the MTH 570

If replacing the cable for the MTH 570, use a power cable with a 4 mm² cross-section.

Installation

15. Specification

15.1 Dimensions

b02	Entry electrical cables I
b03	Entry electrical cables II
c01	Cold water inlet Male thread G 3/8 A
c06	DHW outlet Male thread G 3/8 A

15.2 Wiring diagram

15.2.1 MTH 350-570 1/N/PE ~ 220-240 V

15.3 Increasing the temperature

At 230 V, the following water temperature increases result:

X Flow rate in l/min Y Temperature increase in K 1 3.5 kW - 230 V 2 4.4 kW - 230 V 3 5.7 kW - 230 V

Example MTH 350 with 3.5 kW

Flow rate l/min 2.0
Increasing the temperature K 25
Cold water supply temperature °C 12
Maximum possible outlet temperature °C 37

An outlet temperature of 50 °C can be achieved with the lowest possible flow rate and the following cold water inlet temperatures:

• MTH 350 > 18 °C MTH 440 > 21 °C MTH 570 > 22 °C

15.4 Application areas

For the specific electrical resistance and specific electrical conductivity, see "Data table".

Standard specification at 15 °C			20 °C			25 °C
Spec. resist-anceρ ≥	Spec. conduc-tivity σ ≤		Spec. resist-anceρ ≥	Spec. conduc-tivity σ ≤		Spec. resist-anceρ ≥	Spec. conduc-tivity σ ≤
Ωcm	mS/m	μS/cm	Ωcm	mS/m	μS/cm	Ωcm	mS/m	μS/cm
1100	91	909	970	103	1031	895	112	1117

Installation

15.5 Details on energy consumption

Product data complies with EU regulations relating to the Directive on the ecodesign of energy related products (ErP).

MTH 350 MTH 440 MTH 570 MTH 350 UTE MTH 350 UT MTH 350 OT
		189554	189555	222116	189557	189631	189556
Manufacturer		AEG Haus-technik	AEG Haus-technik	AEG Haus-technik	AEG Haus-technik	AEG Haus-technik	AEG Haus-technik
Load profile		XXS	XXS	XXS	XXS	XXS	XXS
Energy efficiency category		A	A	A	A	A	A
Annual power consumption	kWh	478	478	478	478	478	478
Energy efficiency	%	39	39	39	39	39	39
Sound power level	dB(A)	15	15	15	15	15	15
Special information on measuring the efficiency		None	None	None	None	None	None

15.6 Data table

		MTH 350			MTH 440			MTH 570			MTH 350 UTE			MTH 350 UT			MTH 350 OT
		189554			189555			222116			189557			189631			189556
Electrical details
Rated voltage	V	220	230	240	220	230	240	220	230	240	220	230	240	220	230	240	220	230	240
Rated output	kW	3.2	3.5	3.8	4.0	4.4	4.8	5.2	5.7	6.2	3.2	3.5	3.8	3.2	3.5	3.8
Rated current	A	14.5	15.2	15.8	18.2	19.1	20	23.6	24.7	25.8	14.5	15.2	15.8	14.5	15.2	15.8
Fuse	A	16	16	16	20	20	20	25	25	32	16	16	16	16	16	16
Frequency	Hz	50/60			50/60			50/60			50/60			50/60			50/60
Phases		1/N/PE			1/N/PE			1/N/PE			1/N/PE			1/N/PE			1/N/PE
Max. mains impedance at 50 Hz	Ω							0.394	0.377	0.361

Installation

MTH 350 MTH 440 MTH 70 MTH 350 UTE MTH 350 UT MTH 350 OT
Specific resistance\rho_{15} \geq(at\varthetacold\leq 25^{\circ}C)	\Omegacm	1100	1100	1100	1100	1100	1100
Specific conductivity\sigma_{15} \leq(at\varthetacold\leq 25^{\circ}C)	\mu S/cm	909	909	909	909	909	909
Specific conductivity\sigma_{15} \leq(at\varthetacold>25^{\circ}C)	\mu S/cm	909	909	909	909	909	909
Specific resistance\rho_{15} \geq(at\varthetacold>25^{\circ}C)	\Omegacm	1100	1100	1100	1100	1100	1100
Application limits
Max. throughput	l/min	2.3	2.7	3.5	2.3	2.3
Max. permissible pressure	MPa	0	0	0	0	0	0
Values
Max. permissible inlet temperature	^{\circ}C	35	35	35	35	35	35
ON	l/min	>1.6	>2.0	>2.6	>1.6	>1.6
Pressure drop at flow rate	MPa	0.05	0.06	0.08	0.05	0.05
Flow rate for pressure drop	l/min	1.6	2.0	2.6	1.6	1.6
Flow rate limit at	l/min	2.2	2.8	4.3	2.2	2.2
DHW delivery	l/min	2.0	2.5	3.2	2.0	2.0
\Delta\vartheta$ at DHW delivery	K	25	25	25	25	25	25
Hydraulic data
Rated capacity	I	0.1	0.1	0.1	0.1	0.1	0.1
Versions
Oversink installation		X	X	X	X	X	X
Undersink installation		X	X	X	X	X	X
Open vented type		X	X	X	X	X	X
Protection class		1	1	1	1	1	1
Insulation block		Plastic	Plastic	Plastic	Plastic	Plastic	Plastic
Heating system heat generator		Bare wire	Bare wire	Bare wire	Bare wire	Bare wire	Bare wire
Cap and back panel		Plastic	Plastic	Plastic	Plastic	Plastic	Plastic

Guarantee - Environment and recycling

MTH 350 MTH 440 MTH $70 MTH 350 UTE MTH 350 UT MTH 350 OT
Colour white white white white white white
IP-Rating IP25 IP25 IP25 IP25 IP25 IP25 IP25
Energy data
Energy efficiency class		A	A	A	A	A	A
Dimensions
Height	mm	143	143	143	143	143	143
Width	mm	190	190	190	190	190	190
Depth	mm	82	82	82	82	82	82
Length of connecting cable	mm	700	700	700	700	700	700
Weights
Weight	kg	1.4	1.4	1.4	1.4	1.4	1.4

Guarantee

The guarantee conditions of our German companies do not apply to appliances acquired outside of Germany. In countries where our subsidiaries sell our products a guarantee can only be issued by those subsidiaries. Such guarantee is only granted if the subsidiary has issued its own terms of guarantee. No other guarantee will be granted.

We shall not provide any guarantee for appliances acquired in countries where we have no subsidiary to sell our products. This will not affect warranties issued by any importers.

Environment and recycling

We would ask you to help protect the environment. After use, dispose of the various materials in accordance with national regulations.

Installation

Mounting of the fitting

Urzhumskaya street 4, building 2

129343 Moscow

Tel. [phone]

Fax [phone]

Switzerland

STIEBEL ELTRON AG

Industrie West

Gass 8

5242 Lupfig

Tel. [phone]

Fax [phone]

AEG is a registered trademark used under license from AB Electrolux (publ).

Subject to errors and technical changes!