The MTH hydraulically controlled open (pressureless) small-instantaneous water heater is designed for
supplying an open fitting with hot water. When the draw-off fitting is opened, the heating capacity
switches on automatically and the water is heated. The hot water output is dependent on the cold
water temperature, the heating capacity, and the flow rate.
1.2 The most important points in brief
Temperature adjustment is effected using the fitting:
– To increase the temperature, restrict the flow rate a little.
– For low temperatures, increase the flow rate or mix in cold water.
1.3 Hot water output
TypeOutputhot water output*
MTH 3503.5 kW2.0 l/min
*The built-in automatic flow regulation provides for a constant flow rate. Hot water output with 230 V
mains voltage and a temperature increase of 25 K.
1.3 Important notes
In the case of temperature selection, water temperatures of over 60 °C can be reached at the hot
water outlet. Small children should therefore be kept away from the hot water outlets.
DANGER OF SCALDING!
• If the water feed of the MTH has been interrupted – e.g. because of the danger of frost or work on
the water pipe, the following steps must be taken before the unit is brought back into operation:
1. Remove or switch off fuses.
2. Open a tap downstream of the unit until the unit and the cold water feed pipe are free of air.
3. Replace or switch on fuses again.
• The small-instantaneous water heater must not be exposed to any pressure. Never close off the
fitting outlet and do not use an aerator or a hose with a jet regulator. Furring can close off the outlet
and thus cause the small-instantaneous water heater to be under pressure.
1.5 First actions to be taken in the event of malfunction
• Check the fuses
• Check the fitting for lime scale blockage or dirt accumulation.
See also “3. Fault finding by the user”.
1.6 Maintenance and care
Maintenance work, such as for example checking the electrical safety, may only be carried out by
a qualified installer.
Regularly delime the jet regulator in the fitting and if necessary replace:
Order no.: 25 45 13
A damp cloth is sufficient for care of the unit. Do not use any abrasive or corrosive cleaning agents.
1.7 Operating and installation instructions
Keep these instructions carefully and pass them on to your successor in the event of a change in
ownership, in the event of maintenance and possible repair work they should be passed to the
qualified installer for his attention.
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2. Installation instructions
2.1 Unit structure
1Cold water connection with filter
2Hot water connection
3Cover securing screw
4Unit rear panel
5Unit front cover
6Fixing holes for under-sink installation
7Snap closing catch
2.2 Delivery variants
MTH 350
MTH 350 with AHo 40 MTH
MTH 350 with AHu 40 MTH
MTH 350 with AHEu 40 MTH
For the qualified installer
English
2.3 Important information
Air in the cold water pipe will destroy the bare-wire heating system of the MTH.
If the water supply to the MTH has been interrupted, for example due to the risk of frost or work
on the water pipe, the following steps must be carried out before the system is used again:
1. Disconnect supply or disconnect the fuses.
2. Open a hot water tap downstream of the device for as long as is necessary for the device and the
cold water pipe to be freed of air.
3. Reconnect the supply or connect the fuses again.
All information in these Instructions for Use and Installation must be followed carefully. They provide
important information with regard to safety, operation, installation, and maintenance of the device.
2.4 Brief description
The MTH hydraulically controlled small-instantaneous water heater is a pressureless unit for the
heating of cold water in accordance with WRC Regulations, with which a water tap can be supplied.
The unit is suitable for hand washing basins, for example in guest WC’s, and for under-sink and
over-sink installation.
The bare-wire heating system is suitable for low-lime and limy water (see Table 2 for ranges of use).
2.5 Fittings
Only pressureless fittings may be installed. The MTH must not be exposed to any pressure. Never close
off the fitting outlet. Furring can close off the outlet and impair the function. For optimum jet patterns
use only the jet regulator supplied.
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For the qualified installer
2.6 Regulations and provisions
• Installation (water and electrical installation), as well as the first start-up and maintenance of this
unit, may only be carried out by a qualified installer in accordance with these instructions.
• Faultless operation and operational safety are only guaranteed if the original accessories and spare
parts intended for the unit are used.
• In accordance with IEE and WRC Regulations.
• Regulations of the local energy supply company.
• Regulations of the relevant water supply company.
The following should also be observed:
• The unit rating plate.
• Technical data (see Table 1).
The specific electrical resistance of the water must not be lower than specified on the rating
plate. In the case of a water grid supply network, the lowest electrical resistance of the water is
to be taken into account (see Table 2). Your water supply company will advise you of the
specific electrical resistance or the electrical conductivity of the water.
Water installation:
• A safety valve is not necessary.
• Operating the unit with preheated water is not permitted!
• Fittings for pressurised units are not permitted!
Electrical installation:
• It must be possible to isolate the unit from the main supply on all poles with an isolating distance of
at least 3 mm, for example using fuses.
2.7 Technical data (the data on the unit identification plate are applicable)
TypeMTH 350
Rated power3.5 kW
Rated voltage230 V ~
Rated current15 A
Hot water output ∆ϑ = 25 K2.0 l/min
Flow rate „on“≤ 2.0 l/min
Flow rate „off“≥ 0.9 l/min
Automatic flow regulation2.2 l/min
Pressure drop (during switch-on flow)0.05 MPa
Max. inlet temperature25 °C
Rated capacity0.1 l
Designopen
Weight1.4 kg
Protection class in accordance with EN 603351
Protection mode in accordance with EN 60529IP 25
Test markSee unit identification plate
Structural inspection test certificatePA-No. (Nr. for Germany)
Water connections (external thread)G 3/8, surface installation
Electrical connection1/N/PE ~ 230 V
Heating systemBare-wire
Area of useLow-lime and limy water
Range of use with regard to specific
electrical resistance / conductivitySee Table 2
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Table 1
For the qualified installer
Areas of application for instantaneous water heaters relative to the specific electrical
conductivity / specific electrical resistance of the water
Designation asAreas of application for different water analysis
reference temperatures* designation
Standardatat
at 15 °C20 °C25 °C
Specific electrical resistance≥ 1100,9Ωcm≥1970 Ωcm≥1900 Ωcm
corresponding to
specific electrical conductivity≤ 1190.9 mS/m≤ 1103 mS/m≤ 1111 mS/m
≤1909,9µS/cm≤ 1030 µS/cm≤ 1110 µS/cm
Table 2
* The values for the specific electrical resistance and the specific electrical conductivity are determined
at different temperatures in different regions. This must be taken into account in the evaluation.
2.8 Installation location
The MTH is to be installed, according to choice, as an over-sink or under-sink unit ,
in a closed, frost-free room in the vicinity of the water tap (dismantled unit is to be stored
in a frost-free place, as residual water always remains in the unit).
2.9 Unit installation
Under-sink installation with AHu 40 MTH or AHEu 40 MTH fitting
n Loosen cover securing screws by two turns.
o Using a screwdriver, release the snap closing catch.
p Take off the unit front cover with heating block.
q With the help of a pair of nippers, break out the feed-through opening for the connection cable
(break-off point).
r Fix the unit rear panel to the wall using dowels and screws; use the unit rear panel as a drilling
template.
Installation, last in – first out.
Screw connecting hoses of the AHu 40 MTH or AHEu 40 MTH unit onto the water connections (1 and 2)
(see fittings description), when doing this use a 14 mm spanner on the unit as a counter-force.
Over-sink installation with AHo 40 MTH fitting
The cold water pipe and AHo 40 MTH wall fitting must be safely secured.
1. Screw the AHo 40 MTH wall fitting into the wall disc.
2. Screw the MTH unit onto the fitting; when doing this use a 14 mm spanner on the unit as a
counter-force.
English
Over-sink installation without wall fitting
Installation of the unit as shown in illustration (Gerät um 180 ° gedreht).
2.10 Electrical connection
The unit must be connected to the protective earth terminal.
• This appliance is fitted with a power supply cabel.
15
For the qualified installer
2.11 First start-up
(may only be carried out by a qualified installer)
n
ON
EINEIN
EIN
EINEIN
o
ON
n Fill and deaerate the unit. Note: danger of running dry!
Open and close the tap repeatedly until the pipework and the unit are free of air. For guidance on
air, see „2.3 Important information“.
o Switch on the mains power.
p Test the operating mode of the instantaneous water heater and armature.
Note: the enclosed sticker has to be stucked after unit installation
Handover of the unit
Explain the function of the unit to the user and familiarize him or her with its use.
Important instructions:
• Draw the user’s attention to possible hazards (scalding).
• Hand over these instructions for careful retention.
2.12 Special accessories
• Wall fitting, pressureless, for MTH
• Twin-handle washstand fitting, pressureless, for MTH
• Single lever washstand fitting, pressureless, with pull rod drain for MTH
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37603 Holzminden
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