Technical data

11
4.8 electrical supply
A 240 Volt single phase supply must be present at the proposed boiler location. Wiring external to the
appliance must be in accordance with BS 7671 (the current IEE Wiring Regulations) for electrical installation
and any local regulations which apply.
Wire used for the outdoor sensor, the room unit and the domestic hot water temperature sensor must
have the following minimum cross section, depending upon the cable length.
4.7 gas supply
The Midmat HT boiler is designed and delivered ready for Natural Gas group G20. For operation with
LPG. The LPG conversion kit must be ordered and installed and the multifunctional gas valve adjusted as
necessary. (See section 5.4). The Gas Supplier should be consulted at the installation planning stage in
order to establish the availability of an adequate supply of gas. An existing service pipe MUST NOT be used
without prior consultation with the gas supplier. An existing meter and/or pipework should be of sufficient
size to carry the maximum boiler input plus the demand of any other installed appliance. (BS 6891:1988).
The governor at the meter must give a constant outlet pressure of 20 mbar (8 in. wg) when the
appliance is running on natural gas (G20) or 37 mbar at the regulator when using LPG (G31). The gas supply
should be purged in accordance with IGE/UP/1. WARNING: Before purging open all doors and windows,
also extinguish any cigarettes, pipes and any other naked lights.
The mains cable must be PVC insulated to BS 6500 table 16.
WARNING: THIS APPLIANCE MUST BE EARTHED. (Failure to provide a satisfactory Earth connection
would be a safety hazard and may also result in appliance malfunction).
The method of connection to the mains supply must facilitate complete electrical isolation of the
appliance. A fused double pole switch having a 3mm contact separation in both poles and serving only the
boiler (and its external controls) may be used.
Length m Minimum Cross Section mm
2
Up to 25 0.25
25 ... 50 0.5
70 ... 140 1
Table 5
5.0 installation
instructions
5.1 unpacking the boiler
The boiler is delivered in a fully paletted crate containing the boiler and associated fittings, plus any
other optional ancillary control components in separate cartons.
The boiler crate contains:
● Midimat HT 220/330 boiler.
● Assembly, commissioning and maintenance manual.
● External temperature sensor with screws and plugs.
Built into each unit are the following:
● Siphon for condensation discharge integrated
in exhaust gas collector.
● Flow temperature sensor.
● Thermometer with LCD display.
● Manometer with LCD display.
● SPIRANOX condensing heat exchanger in
austentic (316L) stainless steel.
● ECONOX premix radiant burner,
RPM-controlled.
● Gas control valve, gas/air pressure ratio 1:1.
● Boiler water temperature control.
● Fully automatic ignition.
● Ionisation monitoring.
● Weather-dependent (compensated) control.