Horstmann HRT4-A Operating instructions

1
The HRT4-A is a 230 volt electronic room thermostat designed to provide
optimum comfort with close control of the energy used to heat the home.
These instructions also apply to the HFT4 frost thermostat and the HTT4 tamper
proof thermostat.
INSTALLATION AND CONNECTION OF THE HRT4-A, HFT4 AND HTT4 MUST BE CARRIED
OUT BY A SUITABLY QUALIFIED PERSON.
WARNING: ISOLATE MAINS SUPPLY BEFORE COMMENCING INSTALLATION.
The HRT4-A will only operate on a 230 Volt mains electricity supply and until
power is connected the thermostat will be inoperative.





2
A room thermostat simply switches the heating system on and off as necessary. It works by sensing
the air temperature, switching on the heating when the air temperature falls below the thermostat
setting, and switching it off once this set temperature has been reached.
Turning a room thermostat to a higher setting will not make the room heat up any faster.
How quickly the room heats up depends on the design of the heating system, for example, the size
of boiler and radiators.
Neither does the setting affect how quickly the room cools down. Turning a room
thermostat to a lower setting will result in the room being controlled at a lower
temperature, and saves energy.
The heating system will not work if a time switch or programmer has switched it off.
The way to set and use your room thermostat is to find the lowest temperature setting that you are
comfortable with, and then leave it alone to do its job. The best way to do this is to set the room
thermostat to a low temperature - say 18°C - and then turn it up by one degree each day until
you are comfortable with the temperature. You won’t have to adjust the thermostat further. Any
adjustment above this setting will waste energy and cost you more money.
If your heating system is a boiler with radiators, there will usually be only one room
thermostat to control the whole house. But you can have different temperatures in
individual rooms by installing thermostatic radiator valves (TRVs) on individual radiators.
If you don’t have TRVs, you should choose a temperature that is reasonable for the whole house. If
you do have TRVs, you can choose a slightly higher setting to make sure that even the coldest room
is comfortable, then prevent any overheating in other rooms by adjusting the TRVs.
Room thermostats need a free flow of air to sense the temperature, so they must not be
covered by curtains or blocked by furniture. Nearby electric fires, televisions, wall or table lamps
may prevent the thermostat from working properly.

Set the dial to the required room temperature by lining up the temperature marked on the dial
in degrees C against the setting mark to the left of the dial.
The indicator light will be On when the thermostat is ‘calling’ for heat.
(In other words the thermostat has detected that the room is not warm enough compared to its
set temperature).
If the indicator light is Off then either the room thermostat is sensing that it is warm enough and
has switched Off or that the timeswitch/programmer has switched Off.
N.B. If the timeswitch or programmer has switched Off the thermostat will not operate.
What is a room thermostat?


3
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The HRT4-A should be mounted on an internal wall
approximately 1.5 metres from floor level and should be in a
position away from draughts, direct heat and sunlight. Ensure
that there will be enough space to allow easy access to the
two retaining screws located at the base of the wall plate.
N.B. For the HFT4 Frost Thermostat, locate in the coldest part
of the house to be protected.

To remove the wall plate from the HRT4-A undo the two retaining
screws located on the underside, the wall plate should now be easily
removed. Once the wall plate has been removed from the packaging
please ensure the HRT4-A is re-sealed to prevent damage from dust,
debris etc.
The wall plate should be fitted with the wiring terminals located at
the top and in a position which allows a total clearance of at least
50mm around the HRT4-A thermostat.

Offer the plate to the wall in the position the HRT4-A is to be mounted and mark the fixing positions
through the slots in the wall plate. Drill and plug the wall, then secure the plate in position.
The slots in the wall plate will compensate for any misalignment of the fixings.

The HRT4-A wall plate may be fitted directly on to a single gang steel flush wiring box complying
with BS4662, using two M3.5 screws. The HRT4-A is suitable for mounting on a flat surface only, it
must not be positioned on an unearthed metal surface.

All necessary electrical connections should now be made. Flush wiring can enter from the rear
through the aperture in the wall plate.
The mains supply terminals are intended to be connected to the supply by means of fixed wiring.
The HRT4-A is mains powered and requires a 3 Amp fused spur. The recommended cable size is
1.0mm2.
The HRT4-A is double insulated and does not require an earth connection, an earth connection
block is provided on the backplate for terminating any cable earth conductors. Earth continuity must
be maintained and all bare earth conductors must be sleeved. Ensure that no conductors are left
protruding outside the central space enclosed by the backplate.



4


Maximum load 3 Amps @ 230V AC
230V
50Hz
Mains
supply
230V
50Hz
Mains
supply
Switched live
(call)
Switched live
(call)
L
N
E
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Complete the installation by swinging the room
thermostat into position by engaging with the lugs at
the top of the wall plate before pushing it firmly home
into its plug-in terminal block.
Tighten the 2 captive screws on the underside
of the unit.
Now ensure that the heating system is responding to
the On/Off commands from the room thermostat and
explain its operation to the householder before handing
over these instructions highlighting the ‘explanation for
householders’ on page 2.

These thermostats have an internal connection which makes them only suitable for mains voltage
applications. No additional linking between terminals is required.


1 2 3 4
N
L
E

5

Follow the same instructions as for the HRT4-A but set the temperature using internal setting dial.
Frost thermostats would normally be sited in the most vulnerable part of the building for
maximum protection.
Internal setting dial



    
LIVE 1 1 1 1
NEUTRAL 2 4 4 4
EARTH E - - 3
SWITCHED LIVE 4 3 3 2
    
    
LIVE 1 L L 1
NEUTRAL 2 N N 2
EARTH E E E E
SWITCHED LIVE 4 3 3 3

6

Power Supply 230v 50Hz
Contact rating 3 (1)amp at 230v AC
Temperature accuracy +/- 0.5°C
Contact type Micro disconnection
Dimensions 86mm x 86mm x 36.25mm
Pollution control Degree2
Design standard EN60730 – 2-9
Temperature range HRT4-A 5-30°C
HTT4 10-30°C
HFT4 0-20°C
Rated Impulse voltage Cat 1 - 1500v
Enclosure protection IP30

Thermostats using TPI (Time Proportional Integral) control algorithms will reduce the temperature
swing that normally occurs when using traditional bellows or thermally operated thermostats. As a
consequence, a TPI regulating thermostat will maintain the comfort level far more efficiently than
any traditional thermostat.
When used with a condensing boiler, the TPI thermostat will help
to save energy as the control algorithm allows the boiler to operate
in condensing mode more consistently compared to older types of
thermostat.
• DIL switch numbers 7 and 8 should be set as diagram opposite.
• For Gas boilers set the TPI setting to 6 cycles per hour.
(Default setting)
• For Oil boilers set the TPI setting to 3 cycles per hour.
• For Electric heating set the TPI setting to 12 cycles per hour.

South Bristol Business Park, Roman Farm Road, Bristol BS4 1UP
E-mail: [email protected]o.uk
Web site: www.horstmann.co.uk
Leaflet number P83850 – Issue 1
Switch positions for
different TPI settings.